Shell学习笔记

登陆服务器时输入   telnet 192.168.0.23


各个 shell 可互相切换
ksh:$    sh:$    csh:guangzhou%     bash:bash-3.00$




一、注意事项 
    命令和参数之间必需用空格隔开，参数和参数之间也必需用空格隔开。
    一行不能超过256个字符；大小写有区分。




二、特殊字符含义 
    文件名以“.”开头的都是隐藏文件/目录，只需在文件/目录名前加“.”就可隐藏它。
    ~        表示主目录。    
    .        当前目录(一个点)。    
    ..       上一级目录(两个点)。
    ;        多个命令一起用。
    >  >>    输出重定向  。将一个命令的输出内容写入到一个文件里面。如果该文件存在， 就将该文件的内容覆盖；
             如果不存在就先创建该文件， 然后再写入内容。
             输出重定向，意思就是说，将原来屏幕输出变为文件输出，即将内容输到文件中。
    <  <<    输入重定向。  本来命令是通过键盘得到输入的，但是用小于号，就能够使命令从文件中得到输入。
    \        表示未写完，回车换行再继续。
    *        匹配零个或者多个字符。
    ?        匹配一个字符。
    []       匹配中括号里的内容[a-z][A-Z][0-9]。
    ！       事件。
    !!       执行最近一次的命令
    $        取环境变量的值。
    |        管道。把前一命令的输出作为后一命令的输入，把几个命令连接起来。
             ｜经常跟tee连用，tee 把内容保存到文档并显示出来。




三、通用后接命令符 
    -a    所有(all)。
    -e    所有(every)，比a更详细。
    -f    取消保护。
    -i    添加提示。
    -p    强制执行。
    -r    目录管理。


 分屏显示的中途操作 
    空格       继续打开下一屏；
    回车      继续打开下一行；
    b                另外开上一屏；
    f                另外开下一屏；
    h                帮助；
    q或Ctrl+C        退出；
    /字符串           从上往下查找匹配的字符串；
    ？字符串          从下往上查找匹配的字符串；
    n                继续查找。


四、退出命令 
exit    退出; DOS内部命令 用于退出当前的命令处理器(COMMAND.COM)     恢复前一个命令处理器。
Ctrl+d  跟exit一样效果，表中止本次操作。
logout  当csh时可用来退出，其他shell不可用。


clear   清屏，清除(之前的内容并未删除，只是没看到，拉回上面可以看回)。相当与DOS下的cls




五、目录管理命令 
pwd   显示当前所在目录，查看当前所在目录的完整路径(绝对路径)。
cd    进入某目录，显示或改变当前目录。
      cd回车/cd ~     都是回到自己的主目录。
      cd .            当前目录(空格再加一个点)。
      cd ..           回到上一级目录(空格再加两个点)。    cd ../..  向上两级。
      cd /user/s0807  从绝对路径去到某目录。
      cd ~/s0807      直接进入主目录下的某目录(“cd ~"相当于主目录的路径的简写)。
ls    查看目录或者文件的属性，列举出任一目录下面的文件
      用法  ls [-aAbcCdeEfFghHilLmnopqrRstux1@] [file...]
      ls /etc/   显示某目录下的所有文件和目录，如etc目录下的。
      ls -l      (list)列表显示文件(默认按文件名排序)，
                 显示文件的权限、硬链接数(即包含文件数,普通文件是1，目录1+)、用户、组名、大小、修改日期、文件名。
      ls -t      (time)按修改时间排序，显示目录和文件。
      ls -lt     是“-l”和“-t”的组合，按时间顺序显示列表。
      ls -F      显示文件类型，目录“/ ”结尾；可执行文件“*”结尾；文本文件(none)，没有结尾。
      ls -R      递归显示目录结构。即该目录下的文件和各个副目录下的文件都一一显示。
      ls -a      显示所有文件，包括隐藏文件。


    文件权限 
        r    读权限。对普通文件来说，是读取该文件的权限；对目录来说，是获得该目录下的文件信息。
        w    写权限。对文件，是修改；对目录，是增删文件与子目录。
            (注 删除没有写权限的文件可以用 rm -f ，这是为了操作方便，是人性化的设计)。
        x    执行权限；对目录，是进入该目录
        -    表示没有权限
       形式 - rw- r-- r--  
    其中 第一个是文件类型(-表普通文件，d表目录(directory)，l表软链接文件(link))
    第2~4个是属主，生成文件时登录的人，权限最高，用u表示(user)
    第5~7个是属组，系统管理员分配的同组的一个或几个人，用g表示(group)
    第8~10个是其他人，除属组外的人，用o表示(other)
    所有人，包括属主、属组及其他人，用a表示(all)


chmod  更改权限；
    用法    chmod [-fR] <绝对模式> 文件 ...
            chmod [-fR] <符号模式列表> 文件 ...
      其中  <符号模式列表> 是一个用逗号分隔的表     [ugoa]{+|-|=}[rwxXlstugo]
    chmod u+rw  给用户加权限。同理，u-rw也可以减权限。
    chmod u=rw  给用户赋权限。与加权限不一样，赋权限有覆盖的效果。
    主要形式有如下几种 
    chmod u+rw       chmod u=rw
    chmod u+r, u+w   chmod u+rw,g+w, o+r
chmod u+x filenmame   //只想给自己运行，别人只能读
    chmod 777 (用数字的方式设置权限是最常用的)
    数字表示权限时，各数位分别表示属主(user)、属组(group)及其他人(other)；
      其中，1是执行权(Execute)，2是写权限(Write)，4是读权限(Read)，
      具体权限相当于三种权限的数相加，如7＝1+2+4，即拥有读写和执行权。
    另外,临时文件/目录的权限为rwt，可写却不可删,关机后自动删除；建临时目录:chmod 777 目录名，再chmod +t 目录名。


id 显示用户有效的uid(用户字)和gid(组名)
    用法 id [-ap] [user]
    id 显示自己的。
    id root 显示root的。
    id -a root 显示用户所在组的所有组名(如root用户，是所有组的组员)
df 查看文件系统，查看数据区
    用法 df [-F FSType] [-abeghklntVvZ] [-o FSType 特定选项] [目录 | 块设备 | 资源]
    df -k   以kbytes显示文件大小的查看文件系统方式




六、显示文件内容 
more  分屏显示文件的内容。
      用法   more [-cdflrsuw] [-行] [+行号] [+/模式] [文件名 ...]。
      显示7个信息:用户名 密码 用户id(uid) 组id(gid) 描述信息(一般为空) 用户主目录  login shell(登录shell)
cat   显示文件内容，不分屏(一般用在小文件，大文件显示不下)；合并文件，仅在屏幕上合并，并不改变原文件。
      用法 cat [ -usvtebn ] [-|文件] ...
      如:cat>1.c    //就可以把代码粘帖到1.c文件里，按ctrl+d 保存代码。
 cat 1.c 或more 1.c     //都可以查看里面的内容。
 gcc -o 1 1.c  //将1.c编译成.exe文件，我们可以用此命编译出代码。
tail  实时监控文件，一般用在日志文件，可以只看其中的几行。
      用法 tail [+/-[n][lbc][f]] [文件]
          tail [+/-[n][l][r|f]] [文件]




七、文件/目录的增删 
echo  显示一行内容。
touch 如果文件/目录不存在，则创建新文件/目录；如果文件存在，那么就是更新该文件的最后访问时间，
      用法 touch [-acm] [-r ref_file] 文件...
           touch [-acm] [MMDDhhmm[yy]] 文件...
           touch [-acm] [-t [[CC]YY]MMDDhhmm[.SS]] file...
mkdir 创建目录(必须有创建目录的权限)
      用法 mkdir [-m 模式] [-p] dirname ...
      mkdir dir1/dir2          在dir1下建dir2
      mkdir dir13 dir4 dir5    连建多个
      mkdir ~/games            用户主目录下建(默认在当前目录下创建)
      mkdir -p dir6/dir7/dir8  强制创建dir8；若没有前面的目录，会自动创建dir6和dir7。
                               不用-p时，若没有dir6/dir7，则创建失败。


cp   复制文件/目录
     cp  源文件   目标文件     复制文件；若已有文件则覆盖
     cp -r 源目录 目标目录     复制目录；若已有目录则把源目录复制到目标目录下，
                               没有目标目录时，相当于完全复制源目录，只是文件名不同。
 如：cp beans apple dir2       把beans、apple文件复制到dir2目录下
     cp 1.c netseek/2.c        将1.c拷到netseek目录下并命名为2.c
     cp -i beans apple         增加是否覆盖的提示


mv 移动或重命名文件/目录
    用法 mv [-f] [-i] f1 f2
        mv [-f] [-i] f1 ... fn d1
        mv [-f] [-i] d1 d2
    mv 源文件名 目标文件名   若目标文件名还没有,则是源文件重命名为目标文件；若目标文件已存在，则源文件覆盖目标文件。
    mv 源文件名 目标目录     移动文件
    mv 源目录 目标目录       若目标目录不存在，则源目录重命名；若目标目录已存在，则源目录移动到目标目录下。
 如：mv qib.tgz ../qib.tgz   移到上一级目录


rm  删除文件/目录
    用法 rm [-fiRr] 文件 ...
    rm 文件名     删除文件。
    rm -r 目录名  删除目录。
    rm –f 文件    只要是该文件或者目录的拥有者,无论是否有权限删除,都可以用这个命令参数强行删除。
    rm -rf *      删除所有文件及目录
rmdir 删除空目录。只可以删除空目录。


ln 创建硬链接或软链接，硬链接＝同一文件的多个名字；软链接＝快捷方式
    用法   ln [-f] [-n] [-s] f1 [f2]
          ln [-f] [-n] [-s] f1 ... fn d1
          ln [-f] [-n] -s d1 d2
    ln file1 file1.ln      创建硬链接。感觉是同一文件，删除一个，对另一个没有影响；须两个都删除才算删除。
    ln -s file1 file1.sln  创建软链接。可跨系统操作，冲破操作权限；也是快捷方式。




八、时间显示 
date 显示时间，精确到秒
    用法   date [-u] mmddHHMM[[cc]yy][.SS]
    date [-u] [+format]
    date -a [-]sss[.fff]
cal 显示日历
    cal 9 2008  显示2008年9月的日历；    cal 显示当月的
    用法 cal [ [月] 年 ]


九、帮助
man 对某命令提供帮助解释
    帮助( format and display the on-line manual pages) 
    用法  man [-] [-adFlrt] [-M 路径] [-T 宏软件包] [-s 段] 名称 ...
          man [-] [-adFlrt] [-M path] [-T macro-package]  [-s section]  name...
    man [-M 路径] -k 关键字 ...
    man [-M 路径] -f 文件 ...
如：  man ls 就可以查看ls相关的用法




awk 按一定格式输出(pattern scanning and processing language)
    用法 awk [-Fc] [-f 源代码 | 'cmds'] [文件]




十、vi
    底行模式  / ?  命令模式  i a o 输入模式
    
vi 的使用方法 
 1、光标    h 左    j 下        k 上    l 右
    set nu 显示行号(set nonu)  21  光标停在指定行
    21G             第N行  (G到文件尾，1G到文件头) 如果要将光标移动到文件第一行，那么就按 1G
    H               屏幕头
    M               屏幕中间
    L               屏幕底
    ^  或 shift+6   行首
    $  或 shift+4   行尾
    Ctrl+f          下翻
    Ctrl+b          上翻    


2、输入 (输入模式)
    o       光标往下换一行
    O       (大写字母o)在光标所在行上插入一空行
    i       在光标所在位置的前面插入字母
    a       在光标所在位置的后面插入一个新字母
      退出插入状态。


3、修改替换 
    r        替换一个字符
    dd       删除行，剪切行    (5dd删除5行)
             5,10d  删除 5 至 10 行(包括第 5行和第 10 行)
    x        删除一个字符
    dw       删除词，剪切词。 ( 3dw删除 3 单词)
    cw       替换一个单词。 (cw 和 dw 的区别 cw 删除某一个单词后直接进入编辑模式，而dw删除词后仍处于命令模式)
    cc       替换一行
    C        替换从光标到行尾
    yy       复制行 (用法同下的 Y ，见下行)
    Y        将光标移动到要复制行位置，按yy。当你想粘贴的时候，请将光标移动到你想复制的位置的前一个位置，然后按 p
    yw       复制词
    p        当前行下粘贴
    1,2co3   复制行1，2在行3之后
    4,5m6    移动行4，5在行6之后
    u        当你的前一个命令操作是一个误操作的时候，那么可以按一下 u键，即可复原。只能撤销一次
    r file2  在光标所在处插入另一个文件


    ~        将字母变成大写
    J        可以将当前行与下一行连接起来
    /字符串   从上往下找匹配的字符串
    ?字符串   从下往上找匹配的字符串
    n        继续查找
    1,$s/旧串/新串/g   替换全文(或者  %s/旧串/新串/g)
                      (1表示从第一行开始)    没有g则只替换一次，加g替换所有


4、存盘和退出 
     w            存盘
     w newfile    存成新文件
     wq           存盘再退出VI(或者ZZ或 X)
     q!           强行退出不存盘


查看用户 
users      显示在线用户(仅显示用户名)。
who        显示在线用户，但比users更详细，包括用户名、终端号、登录时间、IP地址。
 who am i  仅显示自己，(但包括用户名、端口、登录时间、IP地址；信息量＝who)。
 whoami    也仅显示自己，但只有用户名(仅显示自己的有效的用户名)。
w          显示比who更多内容，还包括闲置时间、占CPU、平均占用CPU、执行命令。
           用法 w [ -hlsuw ] [ 用户 ]
whereis    查询命令所在目录以及帮助文档所在目录
           如: whereis bin   显示bin所在的目录，将显示为：/usr/local/bin
which      查询该命令所在目录(类似whereis)


su         改变用户，需再输入密码。在不退出登陆的情况下，切换到另外一个人的身份
           用法  su [-] [ username [ arg ... ] ]
 su -      相当于退出再重新登录。
           su -l 用户名(如果用户名缺省，则切换到root状态；将提示输入密码)


查找 
find   查找文件(文件或者目录名以及权限属主等匹配搜索)
    用法 find  [-H | -L] 路径列表 谓词列表
    find / -name perl 从根目录开始查找名为perl的文件。
    find . -mtime 10 -print 从当前目录查找距离现在10天时修改的文件，显示在屏幕上。
           (注 “10”表示第10天的时候；如果是“+10”表示10天以外的范围；“-10”表示10天以内的范围。)
finger 可以让使用者查询一些其他使用者的资料
       如:finger     查看所用用户的使用资料
  finger root   查看root的资料
grep 文件中查找字符；有过滤功能，只列出想要的内容
    用法  grep -hblcnsviw 模式 文件 . . .
    如 grep abc /etc/passwd  在passwd文件下找abc字符
grep success * 　　 查找当前目录下面所有文件里面含有success字符的文件
wc 统计
    -l 统计行数；  -w统计单词数；   -c 统计字符数
    如  grep wang /etc/passwd|wc -l    统计passwd文件含“wang”的行数
du 查看目录情况
    如   du -sk *    不加-s会显示子目录，-k按千字节排序
    用法 du [-a] [-d] [-h|-k] [-r] [-o|-s] [-H|-L] [文件...]


进程管理 
ps 显示进程。
    用法 ps [ -aAdeflcjLPyZ ] [ -o 格式 ] [ -t 项列表 ]
    [ -u 用户列表 ] [ -U 用户列表 ] [ -G 组列表 ]
    [ -p 进程列表 ] [ -g 程序组列表 ] [ -s 标识符列表 ] [ -z 区域列表 ]
    ps 显示自己的进程。
    ps -e  显示每个进程，包括空闲进程。
    ps -f  显示详情。
    ps -ef 组合－e和－f，所有进程的详情。
    ps -U  uidlist(用户列表) 具体查看某人的进程。


kill  可以杀死某个正在进行或者已经是dest状态的进程
pkill 
sleep 


passwd 可以设置口令


history 用户用过的命令
        如: history  可以显示用户过去使用的命令


jobs 
    用法  jobs [-l ]
fg ％n 
bg ％n 
stop ％n 挂起(仅csh能用)
Ctrl+C 
Ctrl+Z 


网络链接 
ping 
    usage  ping host [timeout]
    usage  ping -s [-l | U] [adLnRrv] [-A addr_family] [-c traffic_class] [-g gateway [-g gateway ...]] [-F flow_label] [-I interval] [-i interface] [-P tos] [-p port] [-t ttl] host [data_size] [npackets]


ifconfig -a 
     /sbin/ifconfig    查看本机的IP地址


netstat -rn 




rlogin 


ftp 




mount 加载一个硬件设备
      用法:mount [参数] 要加载的设备 载入点
      如: mount /dev/cdrom
      cd /mnt/cdrom  //进入光盘目录




tar 解压命令
    tar -zxvf nmap-3.45.tgz    将这个解压到nmap-3.45这个目录里






















帮助文件 [sd0807@localhost ~]$       help
GNU bash, version 3.1.17(1)-release (i686-redhat-linux-gnu)
These shell commands are defined internally.  Type `help' to see this list.
Type `help name' to find out more about the function `name'.
Use `info bash' to find out more about the shell in general.
Use `man -k' or `info' to find out more about commands not in this list.


A star (*) next to a name means that the command is disabled.


 JOB_SPEC [&]                            (( expression ))
 . filename [arguments]                       
 [ arg... ]                              [[ expression ]]
 alias [-p] [name[=value] ... ]         bg [job_spec ...]
 bind [-lpvsPVS] [-m keymap] [-f fi     break [n]
 builtin [shell-builtin [arg ...]]      caller [EXPR]
 case WORD in [PATTERN [| PATTERN].     cd [-L|-P] [dir]
 command [-pVv] command [arg ...]       compgen [-abcdefgjksuv] [-o option
 complete [-abcdefgjksuv] [-pr] [-o     continue [n]
 declare [-afFirtx] [-p] [name[=val     dirs [-clpv] [+N] [-N]
 disown [-h] [-ar] [jobspec ...]        echo [-neE] [arg ...]
 enable [-pnds] [-a] [-f filename]      eval [arg ...]
 exec [-cl] [-a name] file [redirec     exit [n]
 export [-nf] [name[=value] ...] or     false
 fc [-e ename] [-nlr] [first] [last     fg [job_spec]
 for NAME [in WORDS ... ;] do COMMA     for (( exp1; exp2; exp3 )); do COM
 function NAME { COMMANDS ; } or NA     getopts optstring name [arg]
 hash [-lr] [-p pathname] [-dt] [na     help [-s] [pattern ...]
 history [-c] [-d offset] [n] or hi     if COMMANDS; then COMMANDS; [ elif
 jobs [-lnprs] [jobspec ...] or job     kill [-s sigspec | -n signum | -si
 let arg [arg ...]                      local name[=value] ...
 logout                                 popd [+N | -N] [-n]
 printf [-v var] format [arguments]     pushd [dir | +N | -N] [-n]
 pwd [-LP]                              read [-ers] [-u fd] [-t timeout] [
 readonly [-af] [name[=value] ...]      return [n]
 select NAME [in WORDS ... ;] do CO     set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
 shift [n]                              shopt [-pqsu] [-o long-option] opt
 source filename [arguments]            suspend [-f]
 test [expr]                            time [-p] PIPELINE
 times                                  trap [-lp] [arg signal_spec ...]
 true                                   type [-afptP] name [name ...]
 typeset [-afFirtx] [-p] name[=valu     ulimit [-SHacdfilmnpqstuvx] [limit
 umask [-p] [-S] [mode]                 unalias [-a] name [name ...]
 unset [-f] [-v] [name ...]             until COMMANDS; do COMMANDS; done
 variables - Some variable names an wait [n]
 while COMMANDS; do COMMANDS; done  { COMMANDS ; }






输入    man help


BASH_BUILTINS(1)                       BASH_BUILTINS(1)


NAME
    bash, :, ., [, alias, bg, bind, break, builtin, cd, command, compgen, complete, continue,
    declare, dirs, disown, echo, enable, eval, exec, exit, export, fc, fg, getopts, hash, help,
    history, jobs, kill, let, local, logout, popd, printf, pushd, pwd, read, readonly, return,
    set, shift, shopt, source, suspend, test, times, trap, type, typeset, ulimit, umask, una-
    lias, unset, wait - bash built-in commands, see bash(1)


BASH BUILTIN COMMANDS
    Unless otherwise noted, each builtin command documented in this section as accepting options
    preceded by - accepts -- to signify the end of the options.  For example, the :, true,
    false, and test builtins do not accept options.
    : [arguments]
       No effect; the command does nothing beyond expanding arguments and performing any
       specified redirections. A zero exit code is returned.


    . filename [arguments]
    source filename [arguments]
       Read and execute commands from filename in the current shell environment and return
       the exit status of the last command executed from filename. If filename does not
       contain a slash, file names in PATH are used to find the directory containing file-
       name.  The file searched for in PATH need not be executable. When bash is not in
       posix mode, the current directory is searched if no file is found in PATH.  If the
       sourcepath option to the shopt builtin command is turned off, the PATH is not
       searched. If any arguments are supplied, they become the positional parameters when
       filename is executed. Otherwise the positional parameters are unchanged. The return
       status is the status of the last command exited within the script (0 if no commands
       are executed), and false if filename is not found or cannot be read.


    alias [-p] [name[=value] ...]
       Alias with no arguments or with the -p option prints the list of aliases in the form
       alias name=value on standard output.  When arguments are supplied, an alias is
       defined for each name whose value is given. A trailing space in value causes the
       next word to be checked for alias substitution when the alias is expanded. For each
       name in the argument list for which no value is supplied, the name and value of the
       alias is printed. Alias returns true unless a name is given for which no alias has
       been defined.


    bg [jobspec ...]
       Resume each suspended job jobspec in the background, as if it had been started with
       &. If jobspec is not present, the shell’s notion of the current job is used.  bg
       jobspec returns 0 unless run when job control is disabled or, when run with job con-
       trol enabled, any specified jobspec was not found or was started without job control.


    bind [-m keymap] [-lpsvPSV]
    bind [-m keymap] [-q function] [-u function] [-r keyseq]
    bind [-m keymap] -f filename
    bind [-m keymap] -x keyseq:shell-command
    bind [-m keymap] keyseq:function-name
    bind readline-command
       Display current readline key and function bindings, bind a key sequence to a readline
       function or macro, or set a readline variable. Each non-option argument is a command
       as it would appear in .inputrc, but each binding or command must be passed as a sepa-
       rate argument; e.g., ’"\C-x\C-r": re-read-init-file’. Options, if supplied, have the
       following meanings:
       -m keymap
           Use keymap as the keymap to be affected by the subsequent bindings. Accept-
           able keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi,
           vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is
           equivalent to emacs-standard.
       -l   List the names of all readline functions.
       -p   Display readline function names and bindings in such a way that they can be
           re-read.
       -P   List current readline function names and bindings.
       -v   Display readline variable names and values in such a way that they can be re-
           read.
       -V   List current readline variable names and values.
       -s   Display readline key sequences bound to macros and the strings they output in
           such a way that they can be re-read.
       -S   Display readline key sequences bound to macros and the strings they output.
       -f filename
           Read key bindings from filename.
       -q function
           Query about which keys invoke the named function.
       -u function
           Unbind all keys bound to the named function.
       -r keyseq
           Remove any current binding for keyseq.
       -x keyseq:shell-command
           Cause shell-command to be executed whenever keyseq is entered.


       The return value is 0 unless an unrecognized option is given or an error occurred.


    break [n]
       Exit from within a for, while, until, or select loop. If n is specified, break n
       levels. n must be ≥ 1. If n is greater than the number of enclosing loops, all
       enclosing loops are exited. The return value is 0 unless the shell is not executing
       a loop when break is executed.


    builtin shell-builtin [arguments]
       Execute the specified shell builtin, passing it arguments, and return its exit sta-
       tus.  This is useful when defining a function whose name is the same as a shell
       builtin, retaining the functionality of the builtin within the function.  The cd
       builtin is commonly redefined this way. The return status is false if shell-builtin
       is not a shell builtin command.


    cd [-L|-P] [dir]
       Change the current directory to dir. The variable HOME is the default dir.  The
       variable CDPATH defines the search path for the directory containing dir. Alterna-
       tive directory names in CDPATH are separated by a colon (:). A null directory name
       in CDPATH is the same as the current directory, i.e., ‘‘.’’. If dir begins with a
       slash (/), then CDPATH is not used. The -P option says to use the physical directory
       structure instead of following symbolic links (see also the -P option to the set
       builtin command); the -L option forces symbolic links to be followed. An argument of
       - is equivalent to $OLDPWD. If a non-empty directory name from CDPATH is used, or if
       - is the first argument, and the directory change is successful, the absolute path-
       name of the new working directory is written to the standard output. The return
       value is true if the directory was successfully changed; false otherwise.


    caller [expr]
       Returns the context of any active subroutine call (a shell function or a script exe-
       cuted with the . or source builtins. Without expr, caller displays the line number
       and source filename of the current subroutine call. If a non-negative integer is
       supplied as expr, caller displays the line number, subroutine name, and source file
       corresponding to that position in the current execution call stack.  This extra
       information may be used, for example, to print a stack trace. The current frame is
       frame 0. The return value is 0 unless the shell is not executing a subroutine call
       or expr does not correspond to a valid position in the call stack.


    command [-pVv] command [arg ...]
       Run command with args suppressing the normal shell function lookup. Only builtin com-
       mands or commands found in the PATH are executed. If the -p option is given, the
       search for command is performed using a default value for PATH that is guaranteed to
       find all of the standard utilities. If either the -V or -v option is supplied, a
       description of command is printed. The -v option causes a single word indicating the
       command or file name used to invoke command to be displayed; the -V option produces a
       more verbose description. If the -V or -v option is supplied, the exit status is 0
       if command was found, and 1 if not. If neither option is supplied and an error
       occurred or command cannot be found, the exit status is 127. Otherwise, the exit
       status of the command builtin is the exit status of command.


    compgen [option] [word]
       Generate possible completion matches for word according to the options, which may be
       any option accepted by the complete builtin with the exception of -p and -r, and
       write the matches to the standard output. When using the -F or -C options, the vari-
       ous shell variables set by the programmable completion facilities, while available,
       will not have useful values.


       The matches will be generated in the same way as if the programmable completion code
       had generated them directly from a completion specification with the same flags. If
       word is specified, only those completions matching word will be displayed.


       The return value is true unless an invalid option is supplied, or no matches were
       generated.


    complete [-abcdefgjksuv] [-o comp-option] [-A action] [-G globpat] [-W wordlist] [-P prefix]
    [-S suffix]
       [-X filterpat] [-F function] [-C command] name [name ...]
    complete -pr [name ...]
       Specify how arguments to each name should be completed. If the -p option is sup-
       plied, or if no options are supplied, existing completion specifications are printed
       in a way that allows them to be reused as input. The -r option removes a completion
       specification for each name, or, if no names are supplied, all completion specifica-
       tions.


       The process of applying these completion specifications when word completion is
       attempted is described above under Programmable Completion.


       Other options, if specified, have the following meanings. The arguments to the -G,
       -W, and -X options (and, if necessary, the -P and -S options) should be quoted to
       protect them from expansion before the complete builtin is invoked.
       -o comp-option
           The comp-option controls several aspects of the compspec’s behavior beyond
           the simple generation of completions. comp-option may be one of:
           bashdefault
               Perform the rest of the default bash completions if the compspec gen-
               erates no matches.
           default Use readline’s default filename completion if the compspec generates
               no matches.
           dirnames
               Perform directory name completion if the compspec generates no
               matches.
           filenames
               Tell readline that the compspec generates filenames, so it can per-
               form any filename-specific processing (like adding a slash to direc-
               tory names or suppressing trailing spaces). Intended to be used with
               shell functions.
           nospace Tell readline not to append a space (the default) to words completed
               at the end of the line.
           plusdirs
               After any matches defined by the compspec are generated, directory
               name completion is attempted and any matches are added to the results
               of the other actions.
       -A action
           The action may be one of the following to generate a list of possible comple-
           tions:
           alias  Alias names. May also be specified as -a.
           arrayvar
               Array variable names.
           binding Readline key binding names.
           builtin Names of shell builtin commands. May also be specified as -b.
           command Command names. May also be specified as -c.
           directory
               Directory names. May also be specified as -d.
           disabled
               Names of disabled shell builtins.
           enabled Names of enabled shell builtins.
           export Names of exported shell variables. May also be specified as -e.
           file  File names. May also be specified as -f.
           function
               Names of shell functions.
           group  Group names. May also be specified as -g.
           helptopic
               Help topics as accepted by the help builtin.
           hostname
               Hostnames, as taken from the file specified by the HOSTFILE shell
               variable.
           job   Job names, if job control is active. May also be specified as -j.
           keyword Shell reserved words. May also be specified as -k.
           running Names of running jobs, if job control is active.
           service Service names. May also be specified as -s.
           setopt Valid arguments for the -o option to the set builtin.
           shopt  Shell option names as accepted by the shopt builtin.
           signal Signal names.
           stopped Names of stopped jobs, if job control is active.
           user  User names. May also be specified as -u.
           variable
               Names of all shell variables. May also be specified as -v.
       -G globpat
           The filename expansion pattern globpat is expanded to generate the possible
           completions.
       -W wordlist
           The wordlist is split using the characters in the IFS special variable as
           delimiters, and each resultant word is expanded.  The possible completions
           are the members of the resultant list which match the word being completed.
       -C command
           command is executed in a subshell environment, and its output is used as the
           possible completions.
       -F function
           The shell function function is executed in the current shell environment.
           When it finishes, the possible completions are retrieved from the value of
           the COMPREPLY array variable.
       -X filterpat
           filterpat is a pattern as used for filename expansion. It is applied to the
           list of possible completions generated by the preceding options and argu-
           ments, and each completion matching filterpat is removed from the list.  A
           leading ! in filterpat negates the pattern; in this case, any completion not
           matching filterpat is removed.
       -P prefix
           prefix is added at the beginning of each possible completion after all other
           options have been applied.
       -S suffix
           suffix is appended to each possible completion after all other options have
           been applied.


       The return value is true unless an invalid option is supplied, an option other than
       -p or -r is supplied without a name argument, an attempt is made to remove a comple-
       tion specification for a name for which no specification exists, or an error occurs
       adding a completion specification.


    continue [n]
       Resume the next iteration of the enclosing for, while, until, or select loop. If n
       is specified, resume at the nth enclosing loop. n must be ≥ 1. If n is greater than
       the number of enclosing loops, the last enclosing loop (the ‘‘top-level’’ loop) is
       resumed. The return value is 0 unless the shell is not executing a loop when con-
       tinue is executed.


    declare [-afFirtx] [-p] [name[=value] ...]
    typeset [-afFirtx] [-p] [name[=value] ...]
       Declare variables and/or give them attributes. If no names are given then display
       the values of variables. The -p option will display the attributes and values of
       each name. When -p is used, additional options are ignored. The -F option inhibits
       the display of function definitions; only the function name and attributes are
       printed.  If the extdebug shell option is enabled using shopt, the source file name
       and line number where the function is defined are displayed as well. The -F option
       implies -f.  The following options can be used to restrict output to variables with
       the specified attribute or to give variables attributes:
       -a   Each name is an array variable (see Arrays above).
       -f   Use function names only.
       -i   The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC
           EVALUATION ) is performed when the variable is assigned a value.
       -r   Make names readonly. These names cannot then be assigned values by subsequent
           assignment statements or unset.
       -t   Give each name the trace attribute. Traced functions inherit the DEBUG and
           RETURN traps from the calling shell. The trace attribute has no special mean-
           ing for variables.
       -x   Mark names for export to subsequent commands via the environment.


       Using ‘+’ instead of ‘-’ turns off the attribute instead, with the exception that +a
       may not be used to destroy an array variable. When used in a function, makes each
       name local, as with the local command. If a variable name is followed by =value, the
       value of the variable is set to value. The return value is 0 unless an invalid
       option is encountered, an attempt is made to define a function using ‘‘-f foo=bar’’,
       an attempt is made to assign a value to a readonly variable, an attempt is made to
       assign a value to an array variable without using the compound assignment syntax (see
       Arrays above), one of the names is not a valid shell variable name, an attempt is
       made to turn off readonly status for a readonly variable, an attempt is made to turn
       off array status for an array variable, or an attempt is made to display a non-exis-
       tent function with -f.


    dirs [-clpv] [+n] [-n]
       Without options, displays the list of currently remembered directories. The default
       display is on a single line with directory names separated by spaces. Directories
       are added to the list with the pushd command; the popd command removes entries from
       the list.
       +n   Displays the nth entry counting from the left of the list shown by dirs when
           invoked without options, starting with zero.
       -n   Displays the nth entry counting from the right of the list shown by dirs when
           invoked without options, starting with zero.
       -c   Clears the directory stack by deleting all of the entries.
       -l   Produces a longer listing; the default listing format uses a tilde to denote
           the home directory.
       -p   Print the directory stack with one entry per line.
       -v   Print the directory stack with one entry per line, prefixing each entry with
           its index in the stack.


       The return value is 0 unless an invalid option is supplied or n indexes beyond the
       end of the directory stack.


    disown [-ar] [-h] [jobspec ...]
       Without options, each jobspec is removed from the table of active jobs.  If the -h
       option is given, each jobspec is not removed from the table, but is marked so that
       SIGHUP is not sent to the job if the shell receives a SIGHUP.  If no jobspec is
       present, and neither the -a nor the -r option is supplied, the current job is used.
       If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r
       option without a jobspec argument restricts operation to running jobs. The return
       value is 0 unless a jobspec does not specify a valid job.


    echo [-neE] [arg ...]
       Output the args, separated by spaces, followed by a newline. The return status is
       always 0. If -n is specified, the trailing newline is suppressed. If the -e option
       is given, interpretation of the following backslash-escaped characters is enabled.
       The -E option disables the interpretation of these escape characters, even on systems
       where they are interpreted by default. The xpg_echo shell option may be used to
       dynamically determine whether or not echo expands these escape characters by default.
       echo does not interpret -- to mean the end of options. echo interprets the following
       escape sequences:
       \a   alert (bell)
       \b   backspace
       \c   suppress trailing newline
       \e   an escape character
       \f   form feed
       \n   new line
       \r   carriage return
       \t   horizontal tab
       \v   vertical tab
       \\   backslash
       \0nnn the eight-bit character whose value is the octal value nnn (zero to three
           octal digits)
       \nnn  the eight-bit character whose value is the octal value nnn (one to three octal
           digits)
       \xHH  the eight-bit character whose value is the hexadecimal value HH (one or two
           hex digits)


    enable [-adnps] [-f filename] [name ...]
       Enable and disable builtin shell commands. Disabling a builtin allows a disk command
       which has the same name as a shell builtin to be executed without specifying a full
       pathname, even though the shell normally searches for builtins before disk commands.
       If -n is used, each name is disabled; otherwise, names are enabled. For example, to
       use the test binary found via the PATH instead of the shell builtin version, run
       ‘‘enable -n test’’.  The -f option means to load the new builtin command name from
       shared object filename, on systems that support dynamic loading. The -d option will
       delete a builtin previously loaded with -f. If no name arguments are given, or if
       the -p option is supplied, a list of shell builtins is printed. With no other option
       arguments, the list consists of all enabled shell builtins. If -n is supplied, only
       disabled builtins are printed. If -a is supplied, the list printed includes all
       builtins, with an indication of whether or not each is enabled. If -s is supplied,
       the output is restricted to the POSIX special builtins. The return value is 0 unless
       a name is not a shell builtin or there is an error loading a new builtin from a
       shared object.


    eval [arg ...]
       The args are read and concatenated together into a single command. This command is
       then read and executed by the shell, and its exit status is returned as the value of
       eval. If there are no args, or only null arguments, eval returns 0.


    exec [-cl] [-a name] [command [arguments]]
       If command is specified, it replaces the shell. No new process is created.  The
       arguments become the arguments to command. If the -l option is supplied, the shell
       places a dash at the beginning of the zeroth arg passed to command.  This is what
       login(1) does.  The -c option causes command to be executed with an empty environ-
       ment. If -a is supplied, the shell passes name as the zeroth argument to the exe-
       cuted command.  If command cannot be executed for some reason, a non-interactive
       shell exits, unless the shell option execfail is enabled, in which case it returns
       failure.  An interactive shell returns failure if the file cannot be executed. If
       command is not specified, any redirections take effect in the current shell, and the
       return status is 0. If there is a redirection error, the return status is 1.


    exit [n]
       Cause the shell to exit with a status of n. If n is omitted, the exit status is that
       of the last command executed. A trap on EXIT is executed before the shell termi-
       nates.


    export [-fn] [name[=word]] ...
    export -p
       The supplied names are marked for automatic export to the environment of subsequently
       executed commands. If the -f option is given, the names refer to functions.  If no
       names are given, or if the -p option is supplied, a list of all names that are
       exported in this shell is printed. The -n option causes the export property to be
       removed from each name. If a variable name is followed by =word, the value of the
       variable is set to word. export returns an exit status of 0 unless an invalid option
       is encountered, one of the names is not a valid shell variable name, or -f is sup-
       plied with a name that is not a function.


    fc [-e ename] [-nlr] [first] [last]
    fc -s [pat=rep] [cmd]
       Fix Command. In the first form, a range of commands from first to last is selected
       from the history list. First and last may be specified as a string (to locate the
       last command beginning with that string) or as a number (an index into the history
       list, where a negative number is used as an offset from the current command number).
       If last is not specified it is set to the current command for listing (so that ‘‘fc
       -l -10’’ prints the last 10 commands) and to first otherwise. If first is not speci-
       fied it is set to the previous command for editing and -16 for listing.


       The -n option suppresses the command numbers when listing. The -r option reverses
       the order of the commands. If the -l option is given, the commands are listed on
       standard output. Otherwise, the editor given by ename is invoked on a file contain-
       ing those commands. If ename is not given, the value of the FCEDIT variable is used,
       and the value of EDITOR if FCEDIT is not set. If neither variable is set, is used.
       When editing is complete, the edited commands are echoed and executed.


       In the second form, command is re-executed after each instance of pat is replaced by
       rep. A useful alias to use with this is ‘‘r="fc -s"’’, so that typing ‘‘r cc’’ runs
       the last command beginning with ‘‘cc’’ and typing ‘‘r’’ re-executes the last command.


       If the first form is used, the return value is 0 unless an invalid option is encoun-
       tered or first or last specify history lines out of range. If the -e option is sup-
       plied, the return value is the value of the last command executed or failure if an
       error occurs with the temporary file of commands. If the second form is used, the
       return status is that of the command re-executed, unless cmd does not specify a valid
       history line, in which case fc returns failure.


    fg [jobspec]
       Resume jobspec in the foreground, and make it the current job. If jobspec is not
       present, the shell’s notion of the current job is used. The return value is that of
       the command placed into the foreground, or failure if run when job control is dis-
       abled or, when run with job control enabled, if jobspec does not specify a valid job
       or jobspec specifies a job that was started without job control.


    getopts optstring name [args]
       getopts is used by shell procedures to parse positional parameters. optstring con-
       tains the option characters to be recognized; if a character is followed by a colon,
       the option is expected to have an argument, which should be separated from it by
       white space. The colon and question mark characters may not be used as option char-
       acters.  Each time it is invoked, getopts places the next option in the shell vari-
       able name, initializing name if it does not exist, and the index of the next argument
       to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the
       shell or a shell script is invoked. When an option requires an argument, getopts
       places that argument into the variable OPTARG. The shell does not reset OPTIND auto-
       matically; it must be manually reset between multiple calls to getopts within the
       same shell invocation if a new set of parameters is to be used.


       When the end of options is encountered, getopts exits with a return value greater
       than zero. OPTIND is set to the index of the first non-option argument, and name is
       set to ?.


       getopts normally parses the positional parameters, but if more arguments are given in
       args, getopts parses those instead.


       getopts can report errors in two ways. If the first character of optstring is a
       colon, silent error reporting is used. In normal operation diagnostic messages are
       printed when invalid options or missing option arguments are encountered.  If the
       variable OPTERR is set to 0, no error messages will be displayed, even if the first
       character of optstring is not a colon.


       If an invalid option is seen, getopts places ? into name and, if not silent, prints
       an error message and unsets OPTARG. If getopts is silent, the option character found
       is placed in OPTARG and no diagnostic message is printed.


       If a required argument is not found, and getopts is not silent, a question mark (?)
       is placed in name, OPTARG is unset, and a diagnostic message is printed. If getopts
       is silent, then a colon (:) is placed in name and OPTARG is set to the option charac-
       ter found.


       getopts returns true if an option, specified or unspecified, is found. It returns
       false if the end of options is encountered or an error occurs.


    hash [-lr] [-p filename] [-dt] [name]
       For each name, the full file name of the command is determined by searching the
       directories in $PATH and remembered. If the -p option is supplied, no path search is
       performed, and filename is used as the full file name of the command. The -r option
       causes the shell to forget all remembered locations. The -d option causes the shell
       to forget the remembered location of each name. If the -t option is supplied, the
       full pathname to which each name corresponds is printed. If multiple name arguments
       are supplied with -t, the name is printed before the hashed full pathname.  The -l
       option causes output to be displayed in a format that may be reused as input. If no
       arguments are given, or if only -l is supplied, information about remembered commands
       is printed.  The return status is true unless a name is not found or an invalid
       option is supplied.


    help [-s] [pattern]
       Display helpful information about builtin commands. If pattern is specified, help
       gives detailed help on all commands matching pattern; otherwise help for all the
       builtins and shell control structures is printed. The -s option restricts the infor-
       mation displayed to a short usage synopsis. The return status is 0 unless no command
       matches pattern.


    history [n]
    history -c
    history -d offset
    history -anrw [filename]
    history -p arg [arg ...]
    history -s arg [arg ...]
       With no options, display the command history list with line numbers.  Lines listed
       with a * have been modified. An argument of n lists only the last n lines. If the
       shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for
       strftime(3) to display the time stamp associated with each displayed history entry.
       No intervening blank is printed between the formatted time stamp and the history
       line.  If filename is supplied, it is used as the name of the history file; if not,
       the value of HISTFILE is used. Options, if supplied, have the following meanings:
       -c   Clear the history list by deleting all the entries.
       -d offset
           Delete the history entry at position offset.
       -a   Append the ‘‘new’’ history lines (history lines entered since the beginning of
           the current bash session) to the history file.
       -n   Read the history lines not already read from the history file into the current
           history list. These are lines appended to the history file since the begin-
           ning of the current bash session.
       -r   Read the contents of the history file and use them as the current history.
       -w   Write the current history to the history file, overwriting the history file’s
           contents.
       -p   Perform history substitution on the following args and display the result on
           the standard output.  Does not store the results in the history list. Each
           arg must be quoted to disable normal history expansion.
       -s   Store the args in the history list as a single entry. The last command in the
           history list is removed before the args are added.


       If the HISTTIMEFORMAT is set, the time stamp information associated with each history
       entry is written to the history file. The return value is 0 unless an invalid option
       is encountered, an error occurs while reading or writing the history file, an invalid
       offset is supplied as an argument to -d, or the history expansion supplied as an
       argument to -p fails.


    jobs [-lnprs] [ jobspec ... ]
    jobs -x command [ args ... ]
       The first form lists the active jobs. The options have the following meanings:
       -l   List process IDs in addition to the normal information.
       -p   List only the process ID of the job’s process group leader.
       -n   Display information only about jobs that have changed status since the user
           was last notified of their status.
       -r   Restrict output to running jobs.
       -s   Restrict output to stopped jobs.


       If jobspec is given, output is restricted to information about that job. The return
       status is 0 unless an invalid option is encountered or an invalid jobspec is sup-
       plied.


       If the -x option is supplied, jobs replaces any jobspec found in command or args with
       the corresponding process group ID, and executes command passing it args, returning
       its exit status.


    kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
    kill -l [sigspec | exit_status]
       Send the signal named by sigspec or signum to the processes named by pid or jobspec.
       sigspec is either a case-insensitive signal name such as SIGKILL (with or without the
       SIG prefix) or a signal number; signum is a signal number.  If sigspec is not
       present, then SIGTERM is assumed. An argument of -l lists the signal names. If any
       arguments are supplied when -l is given, the names of the signals corresponding to
       the arguments are listed, and the return status is 0. The exit_status argument to -l
       is a number specifying either a signal number or the exit status of a process termi-
       nated by a signal. kill returns true if at least one signal was successfully sent,
       or false if an error occurs or an invalid option is encountered.


    let arg [arg ...]
       Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION). If
       the last arg evaluates to 0, let returns 1; 0 is returned otherwise.


    local [option] [name[=value] ...]
       For each argument, a local variable named name is created, and assigned value. The
       option can be any of the options accepted by declare. When local is used within a
       function, it causes the variable name to have a visible scope restricted to that
       function and its children. With no operands, local writes a list of local variables
       to the standard output. It is an error to use local when not within a function. The
       return status is 0 unless local is used outside a function, an invalid name is sup-
       plied, or name is a readonly variable.


    logout Exit a login shell.


    popd [-n] [+n] [-n]
       Removes entries from the directory stack. With no arguments, removes the top direc-
       tory from the stack, and performs a cd to the new top directory. Arguments, if sup-
       plied, have the following meanings:
       +n   Removes the nth entry counting from the left of the list shown by dirs, start-
           ing with zero. For example: ‘‘popd +0’’ removes the first directory, ‘‘popd
           +1’’ the second.
       -n   Removes the nth entry counting from the right of the list shown by dirs,
           starting with zero. For example: ‘‘popd -0’’ removes the last directory,
           ‘‘popd -1’’ the next to last.
       -n   Suppresses the normal change of directory when removing directories from the
           stack, so that only the stack is manipulated.


       If the popd command is successful, a dirs is performed as well, and the return status
       is 0. popd returns false if an invalid option is encountered, the directory stack is
       empty, a non-existent directory stack entry is specified, or the directory change
       fails.


    printf [-v var] format [arguments]
       Write the formatted arguments to the standard output under the control of the format.
       The format is a character string which contains three types of objects: plain charac-
       ters, which are simply copied to standard output, character escape sequences, which
       are converted and copied to the standard output, and format specifications, each of
       which causes printing of the next successive argument. In addition to the standard
       printf(1) formats, %b causes printf to expand backslash escape sequences in the cor-
       responding argument (except that \c terminates output, backslashes in \', \", and \?
       are not removed, and octal escapes beginning with \0 may contain up to four digits),
       and %q causes printf to output the corresponding argument in a format that can be
       reused as shell input.


       The -v option causes the output to be assigned to the variable var rather than being
       printed to the standard output.


       The format is reused as necessary to consume all of the arguments. If the format
       requires more arguments than are supplied, the extra format specifications behave as
       if a zero value or null string, as appropriate, had been supplied. The return value
       is zero on success, non-zero on failure.


    pushd [-n] [dir]
    pushd [-n] [+n] [-n]
       Adds a directory to the top of the directory stack, or rotates the stack, making the
       new top of the stack the current working directory. With no arguments, exchanges the
       top two directories and returns 0, unless the directory stack is empty.  Arguments,
       if supplied, have the following meanings:
       +n   Rotates the stack so that the nth directory (counting from the left of the
           list shown by dirs, starting with zero) is at the top.
       -n   Rotates the stack so that the nth directory (counting from the right of the
           list shown by dirs, starting with zero) is at the top.
       -n   Suppresses the normal change of directory when adding directories to the
           stack, so that only the stack is manipulated.
       dir  Adds dir to the directory stack at the top, making it the new current working
           directory.


       If the pushd command is successful, a dirs is performed as well. If the first form
       is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd
       returns 0 unless the directory stack is empty, a non-existent directory stack element
       is specified, or the directory change to the specified new current directory fails.


    pwd [-LP]
       Print the absolute pathname of the current working directory. The pathname printed
       contains no symbolic links if the -P option is supplied or the -o physical option to
       the set builtin command is enabled. If the -L option is used, the pathname printed
       may contain symbolic links.  The return status is 0 unless an error occurs while
       reading the name of the current directory or an invalid option is supplied.


    read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d delim] [name ...]
       One line is read from the standard input, or from the file descriptor fd supplied as
       an argument to the -u option, and the first word is assigned to the first name, the
       second word to the second name, and so on, with leftover words and their intervening
       separators assigned to the last name. If there are fewer words read from the input
       stream than names, the remaining names are assigned empty values. The characters in
       IFS are used to split the line into words. The backslash character (\) may be used
       to remove any special meaning for the next character read and for line continuation.
       Options, if supplied, have the following meanings:
       -a aname
           The words are assigned to sequential indices of the array variable aname,
           starting at 0. aname is unset before any new values are assigned. Other name
           arguments are ignored.
       -d delim
           The first character of delim is used to terminate the input line, rather than
           newline.
       -e   If the standard input is coming from a terminal, readline (see READLINE above)
           is used to obtain the line.
       -n nchars
           read returns after reading nchars characters rather than waiting for a com-
           plete line of input.
       -p prompt
           Display prompt on standard error, without a trailing newline, before attempt-
           ing to read any input. The prompt is displayed only if input is coming from a
           terminal.
       -r   Backslash does not act as an escape character. The backslash is considered to
           be part of the line. In particular, a backslash-newline pair may not be used
           as a line continuation.
       -s   Silent mode. If input is coming from a terminal, characters are not echoed.
       -t timeout
           Cause read to time out and return failure if a complete line of input is not
           read within timeout seconds. This option has no effect if read is not reading
           input from the terminal or a pipe.
       -u fd Read input from file descriptor fd.


       If no names are supplied, the line read is assigned to the variable REPLY.  The
       return code is zero, unless end-of-file is encountered, read times out, or an invalid
       file descriptor is supplied as the argument to -u.


    readonly [-apf] [name[=word] ...]
       The given names are marked readonly; the values of these names may not be changed by
       subsequent assignment. If the -f option is supplied, the functions corresponding to
       the names are so marked. The -a option restricts the variables to arrays.  If no
       name arguments are given, or if the -p option is supplied, a list of all readonly
       names is printed. The -p option causes output to be displayed in a format that may
       be reused as input. If a variable name is followed by =word, the value of the vari-
       able is set to word. The return status is 0 unless an invalid option is encountered,
       one of the names is not a valid shell variable name, or -f is supplied with a name
       that is not a function.


    return [n]
       Causes a function to exit with the return value specified by n. If n is omitted, the
       return status is that of the last command executed in the function body. If used
       outside a function, but during execution of a script by the . (source) command, it
       causes the shell to stop executing that script and return either n or the exit status
       of the last command executed within the script as the exit status of the script.  If
       used outside a function and not during execution of a script by ., the return status
       is false. Any command associated with the RETURN trap is executed before execution
       resumes after the function or script.


    set [--abefhkmnptuvxBCHP] [-o option] [arg ...]
       Without options, the name and value of each shell variable are displayed in a format
       that can be reused as input for setting or resetting the currently-set variables.
       Read-only variables cannot be reset. In posix mode, only shell variables are listed.
       The output is sorted according to the current locale. When options are specified,
       they set or unset shell attributes. Any arguments remaining after the options are
       processed are treated as values for the positional parameters and are assigned, in
       order, to $1, $2, ... $n. Options, if specified, have the following meanings:
       -a   Automatically mark variables and functions which are modified or created for
           export to the environment of subsequent commands.
       -b   Report the status of terminated background jobs immediately, rather than
           before the next primary prompt. This is effective only when job control is
           enabled.
       -e   Exit immediately if a simple command (see SHELL GRAMMAR above) exits with a
           non-zero status.  The shell does not exit if the command that fails is part
           of the command list immediately following a while or until keyword, part of
           the test in an if statement, part of a && or ││ list, or if the command’s
           return value is being inverted via !. A trap on ERR, if set, is executed
           before the shell exits.
       -f   Disable pathname expansion.
       -h   Remember the location of commands as they are looked up for execution. This
           is enabled by default.
       -k   All arguments in the form of assignment statements are placed in the environ-
           ment for a command, not just those that precede the command name.
       -m   Monitor mode.  Job control is enabled. This option is on by default for
           interactive shells on systems that support it (see JOB CONTROL above). Back-
           ground processes run in a separate process group and a line containing their
           exit status is printed upon their completion.
       -n   Read commands but do not execute them. This may be used to check a shell
           script for syntax errors. This is ignored by interactive shells.
       -o option-name
           The option-name can be one of the following:
           allexport
               Same as -a.
           braceexpand
               Same as -B.
           emacs  Use an emacs-style command line editing interface. This is enabled
               by default when the shell is interactive, unless the shell is started
               with the --noediting option.
           errtrace
               Same as -E.
           functrace
               Same as -T.
           errexit Same as -e.
           hashall Same as -h.
           histexpand
               Same as -H.
           history Enable command history, as described above under HISTORY. This
               option is on by default in interactive shells.
           ignoreeof
               The effect is as if the shell command ‘‘IGNOREEOF=10’’ had been exe-
               cuted (see Shell Variables above).
           keyword Same as -k.
           monitor Same as -m.
           noclobber
               Same as -C.
           noexec Same as -n.
           noglob Same as -f. nolog Currently ignored.
           notify Same as -b.
           nounset Same as -u.
           onecmd Same as -t.
           physical
               Same as -P.
           pipefail
               If set, the return value of a pipeline is the value of the last
               (rightmost) command to exit with a non-zero status, or zero if all
               commands in the pipeline exit successfully. This option is disabled
               by default.
           posix  Change the behavior of bash where the default operation differs from
               the POSIX 1003.2 standard to match the standard (posix mode).
           privileged
               Same as -p.
           verbose Same as -v.
           vi   Use a vi-style command line editing interface.
           xtrace Same as -x.
           If -o is supplied with no option-name, the values of the current options are
           printed. If +o is supplied with no option-name, a series of set commands to
           recreate the current option settings is displayed on the standard output.
       -p   Turn on privileged mode. In this mode, the $ENV and $BASH_ENV files are not
           processed, shell functions are not inherited from the environment, and the
           SHELLOPTS variable, if it appears in the environment, is ignored. If the
           shell is started with the effective user (group) id not equal to the real
           user (group) id, and the -p option is not supplied, these actions are taken
           and the effective user id is set to the real user id. If the -p option is
           supplied at startup, the effective user id is not reset. Turning this option
           off causes the effective user and group ids to be set to the real user and
           group ids.
       -t   Exit after reading and executing one command.
       -u   Treat unset variables as an error when performing parameter expansion. If
           expansion is attempted on an unset variable, the shell prints an error mes-
           sage, and, if not interactive, exits with a non-zero status.
       -v   Print shell input lines as they are read.
       -x   After expanding each simple command, for command, case command, select com-
           mand, or arithmetic for command, display the expanded value of PS4, followed
           by the command and its expanded arguments or associated word list.
       -B   The shell performs brace expansion (see Brace Expansion above). This is on
           by default.
       -C   If set, bash does not overwrite an existing file with the >, >&, and <> redi-
           rection operators.  This may be overridden when creating output files by
           using the redirection operator >| instead of >.
       -E   If set, any trap on ERR is inherited by shell functions, command substitu-
           tions, and commands executed in a subshell environment. The ERR trap is nor-
           mally not inherited in such cases.
       -H   Enable ! style history substitution. This option is on by default when the
           shell is interactive.
       -P   If set, the shell does not follow symbolic links when executing commands such
           as cd that change the current working directory. It uses the physical direc-
           tory structure instead. By default, bash follows the logical chain of direc-
           tories when performing commands which change the current directory.
       -T   If set, any traps on DEBUG and RETURN are inherited by shell functions, com-
           mand substitutions, and commands executed in a subshell environment. The
           DEBUG and RETURN traps are normally not inherited in such cases.
       --   If no arguments follow this option, then the positional parameters are unset.
           Otherwise, the positional parameters are set to the args, even if some of
           them begin with a -.
       -    Signal the end of options, cause all remaining args to be assigned to the
           positional parameters.  The -x and -v options are turned off. If there are
           no args, the positional parameters remain unchanged.


       The options are off by default unless otherwise noted. Using + rather than - causes
       these options to be turned off. The options can also be specified as arguments to an
       invocation of the shell. The current set of options may be found in $-. The return
       status is always true unless an invalid option is encountered.


    shift [n]
       The positional parameters from n+1 ... are renamed to $1 .... Parameters represented
       by the numbers $# down to $#-n+1 are unset. n must be a non-negative number less
       than or equal to $#. If n is 0, no parameters are changed. If n is not given, it is
       assumed to be 1. If n is greater than $#, the positional parameters are not changed.
       The return status is greater than zero if n is greater than $# or less than zero;
       otherwise 0.


    shopt [-pqsu] [-o] [optname ...]
       Toggle the values of variables controlling optional shell behavior. With no options,
       or with the -p option, a list of all settable options is displayed, with an indica-
       tion of whether or not each is set. The -p option causes output to be displayed in a
       form that may be reused as input. Other options have the following meanings:
       -s   Enable (set) each optname.
       -u   Disable (unset) each optname.
       -q   Suppresses normal output (quiet mode); the return status indicates whether the
           optname is set or unset. If multiple optname arguments are given with -q, the
           return status is zero if all optnames are enabled; non-zero otherwise.
       -o   Restricts the values of optname to be those defined for the -o option to the
           set builtin.


       If either -s or -u is used with no optname arguments, the display is limited to those
       options which are set or unset, respectively. Unless otherwise noted, the shopt
       options are disabled (unset) by default.


       The return status when listing options is zero if all optnames are enabled, non-zero
       otherwise.  When setting or unsetting options, the return status is zero unless an
       optname is not a valid shell option.


       The list of shopt options is:


       cdable_vars
           If set, an argument to the cd builtin command that is not a directory is
           assumed to be the name of a variable whose value is the directory to change
           to.
       cdspell If set, minor errors in the spelling of a directory component in a cd command
           will be corrected. The errors checked for are transposed characters, a miss-
           ing character, and one character too many. If a correction is found, the
           corrected file name is printed, and the command proceeds. This option is
           only used by interactive shells.
       checkhash
           If set, bash checks that a command found in the hash table exists before try-
           ing to execute it.  If a hashed command no longer exists, a normal path
           search is performed.
       checkwinsize
           If set, bash checks the window size after each command and, if necessary,
           updates the values of LINES and COLUMNS.
       cmdhist If set, bash attempts to save all lines of a multiple-line command in the
           same history entry. This allows easy re-editing of multi-line commands.
       dotglob If set, bash includes filenames beginning with a ‘.’ in the results of path-
           name expansion.
       execfail
           If set, a non-interactive shell will not exit if it cannot execute the file
           specified as an argument to the exec builtin command. An interactive shell
           does not exit if exec fails.
       expand_aliases
           If set, aliases are expanded as described above under ALIASES. This option
           is enabled by default for interactive shells.
       extdebug
           If set, behavior intended for use by debuggers is enabled:
           1.   The -F option to the declare builtin displays the source file name and
               line number corresponding to each function name supplied as an argu-
               ment.
           2.   If the command run by the DEBUG trap returns a non-zero value, the
               next command is skipped and not executed.
           3.   If the command run by the DEBUG trap returns a value of 2, and the
               shell is executing in a subroutine (a shell function or a shell script
               executed by the . or source builtins), a call to return is simulated.
           4.   BASH_ARGC and BASH_ARGV are updated as described in their descriptions
               above.
           5.   Function tracing is enabled: command substitution, shell functions,
               and subshells invoked with ( command ) inherit the DEBUG and RETURN
               traps.
           6.   Error tracing is enabled: command substitution, shell functions, and
               subshells invoked with ( command ) inherit the ERROR trap.
       extglob If set, the extended pattern matching features described above under Pathname
           Expansion are enabled.
       extquote
           If set, $'string' and $"string" quoting is performed within ${parameter}
           expansions enclosed in double quotes. This option is enabled by default.
       failglob
           If set, patterns which fail to match filenames during pathname expansion
           result in an expansion error.
       force_fignore
           If set, the suffixes specified by the FIGNORE shell variable cause words to
           be ignored when performing word completion even if the ignored words are the
           only possible completions.  See SHELL VARIABLES above for a description of
           FIGNORE. This option is enabled by default.
       gnu_errfmt
           If set, shell error messages are written in the standard GNU error message
           format.
       histappend
           If set, the history list is appended to the file named by the value of the
           HISTFILE variable when the shell exits, rather than overwriting the file.
       histreedit
           If set, and readline is being used, a user is given the opportunity to re-
           edit a failed history substitution.
       histverify
           If set, and readline is being used, the results of history substitution are
           not immediately passed to the shell parser. Instead, the resulting line is
           loaded into the readline editing buffer, allowing further modification.
       hostcomplete
           If set, and readline is being used, bash will attempt to perform hostname
           completion when a word containing a @ is being completed (see Completing
           under READLINE above). This is enabled by default.
       huponexit
           If set, bash will send SIGHUP to all jobs when an interactive login shell
           exits.
       interactive_comments
           If set, allow a word beginning with # to cause that word and all remaining
           characters on that line to be ignored in an interactive shell (see COMMENTS
           above). This option is enabled by default.
       lithist If set, and the cmdhist option is enabled, multi-line commands are saved to
           the history with embedded newlines rather than using semicolon separators
           where possible.
       login_shell
           The shell sets this option if it is started as a login shell (see INVOCATION
           above). The value may not be changed.
       mailwarn
           If set, and a file that bash is checking for mail has been accessed since the
           last time it was checked, the message ‘‘The mail in mailfile has been read’’
           is displayed.
       no_empty_cmd_completion
           If set, and readline is being used, bash will not attempt to search the PATH
           for possible completions when completion is attempted on an empty line.
       nocaseglob
           If set, bash matches filenames in a case-insensitive fashion when performing
           pathname expansion (see Pathname Expansion above).
       nocasematch
           If set, bash matches patterns in a case-insensitive fashion when performing
           matching while executing case or [[ conditional commands.
       nullglob
           If set, bash allows patterns which match no files (see Pathname Expansion
           above) to expand to a null string, rather than themselves.
       progcomp
           If set, the programmable completion facilities (see Programmable Completion
           above) are enabled. This option is enabled by default.
       promptvars
           If set, prompt strings undergo parameter expansion, command substitution,
           arithmetic expansion, and quote removal after being expanded as described in
           PROMPTING above. This option is enabled by default.
       restricted_shell
           The shell sets this option if it is started in restricted mode (see
           RESTRICTED SHELL below).  The value may not be changed. This is not reset
           when the startup files are executed, allowing the startup files to discover
           whether or not a shell is restricted.
       shift_verbose
           If set, the shift builtin prints an error message when the shift count
           exceeds the number of positional parameters.
       sourcepath
           If set, the source (.) builtin uses the value of PATH to find the directory
           containing the file supplied as an argument. This option is enabled by
           default.
       xpg_echo
           If set, the echo builtin expands backslash-escape sequences by default.
    suspend [-f]
       Suspend the execution of this shell until it receives a SIGCONT signal.  The -f
       option says not to complain if this is a login shell; just suspend anyway. The
       return status is 0 unless the shell is a login shell and -f is not supplied, or if
       job control is not enabled.
    test expr
    [ expr ]
       Return a status of 0 or 1 depending on the evaluation of the conditional expression
       expr. Each operator and operand must be a separate argument. Expressions are com-
       posed of the primaries described above under CONDITIONAL EXPRESSIONS. test does not
       accept any options, nor does it accept and ignore an argument of -- as signifying the
       end of options.


       Expressions may be combined using the following operators, listed in decreasing order
       of precedence.
       ! expr True if expr is false.
       ( expr )
           Returns the value of expr. This may be used to override the normal precedence
           of operators.
       expr1 -a expr2
           True if both expr1 and expr2 are true.
       expr1 -o expr2
           True if either expr1 or expr2 is true.


       test and [ evaluate conditional expressions using a set of rules based on the number
       of arguments.


       0 arguments
           The expression is false.
       1 argument
           The expression is true if and only if the argument is not null.
       2 arguments
           If the first argument is !, the expression is true if and only if the second
           argument is null. If the first argument is one of the unary conditional oper-
           ators listed above under CONDITIONAL EXPRESSIONS, the expression is true if
           the unary test is true. If the first argument is not a valid unary condi-
           tional operator, the expression is false.
       3 arguments
           If the second argument is one of the binary conditional operators listed above
           under CONDITIONAL EXPRESSIONS, the result of the expression is the result of
           the binary test using the first and third arguments as operands. If the first
           argument is !, the value is the negation of the two-argument test using the
           second and third arguments. If the first argument is exactly ( and the third
           argument is exactly ), the result is the one-argument test of the second argu-
           ment. Otherwise, the expression is false. The -a and -o operators are con-
           sidered binary operators in this case.
       4 arguments
           If the first argument is !, the result is the negation of the three-argument
           expression composed of the remaining arguments. Otherwise, the expression is
           parsed and evaluated according to precedence using the rules listed above.
       5 or more arguments
           The expression is parsed and evaluated according to precedence using the rules
           listed above.


    times Print the accumulated user and system times for the shell and for processes run from
       the shell. The return status is 0.


    trap [-lp] [[arg] sigspec ...]
       The command arg is to be read and executed when the shell receives signal(s) sigspec.
       If arg is absent (and there is a single sigspec) or -, each specified signal is reset
       to its original disposition (the value it had upon entrance to the shell). If arg is
       the null string the signal specified by each sigspec is ignored by the shell and by
       the commands it invokes. If arg is not present and -p has been supplied, then the
       trap commands associated with each sigspec are displayed. If no arguments are sup-
       plied or if only -p is given, trap prints the list of commands associated with each
       signal. The -l option causes the shell to print a list of signal names and their
       corresponding numbers.  Each sigspec is either a signal name defined in ,
       or a signal number. Signal names are case insensitive and the SIG prefix is
       optional.  If a sigspec is EXIT (0) the command arg is executed on exit from the
       shell. If a sigspec is DEBUG, the command arg is executed before every simple com-
       mand, for command, case command, select command, every arithmetic for command, and
       before the first command executes in a shell function (see SHELL GRAMMAR above).
       Refer to the description of the extdebug option to the shopt builtin for details of
       its effect on the DEBUG trap. If a sigspec is ERR, the command arg is executed when-
       ever a simple command has a non-zero exit status, subject to the following condi-
       tions. The ERR trap is not executed if the failed command is part of the command
       list immediately following a while or until keyword, part of the test in an if state-
       ment, part of a && or ││ list, or if the command’s return value is being inverted via
       !.  These are the same conditions obeyed by the errexit option. If a sigspec is
       RETURN, the command arg is executed each time a shell function or a script executed
       with the . or source builtins finishes executing. Signals ignored upon entry to the
       shell cannot be trapped or reset. Trapped signals are reset to their original values
       in a child process when it is created. The return status is false if any sigspec is
       invalid; otherwise trap returns true.


    type [-aftpP] name [name ...]
       With no options, indicate how each name would be interpreted if used as a command
       name. If the -t option is used, type prints a string which is one of alias, keyword,
       function, builtin, or file if name is an alias, shell reserved word, function,
       builtin, or disk file, respectively.  If the name is not found, then nothing is
       printed, and an exit status of false is returned. If the -p option is used, type
       either returns the name of the disk file that would be executed if name were speci-
       fied as a command name, or nothing if ‘‘type -t name’’ would not return file. The -P
       option forces a PATH search for each name, even if ‘‘type -t name’’ would not return
       file. If a command is hashed, -p and -P print the hashed value, not necessarily the
       file that appears first in PATH. If the -a option is used, type prints all of the
       places that contain an executable named name. This includes aliases and functions,
       if and only if the -p option is not also used. The table of hashed commands is not
       consulted when using -a. The -f option suppresses shell function lookup, as with the
       command builtin. type returns true if any of the arguments are found, false if none
       are found.


    ulimit [-SHacdefilmnpqrstuvx [limit]]
       Provides control over the resources available to the shell and to processes started
       by it, on systems that allow such control. The -H and -S options specify that the
       hard or soft limit is set for the given resource. A hard limit cannot be increased
       once it is set; a soft limit may be increased up to the value of the hard limit. If
       neither -H nor -S is specified, both the soft and hard limits are set. The value of
       limit can be a number in the unit specified for the resource or one of the special
       values hard, soft, or unlimited, which stand for the current hard limit, the current
       soft limit, and no limit, respectively. If limit is omitted, the current value of
       the soft limit of the resource is printed, unless the -H option is given. When more
       than one resource is specified, the limit name and unit are printed before the value.
       Other options are interpreted as follows:
       -a   All current limits are reported
       -c   The maximum size of core files created
       -d   The maximum size of a process’s data segment
       -e   The maximum scheduling priority (‘nice’)
       -f   The maximum size of files created by the shell
       -i   The maximum number of pending signals
       -l   The maximum size that may be locked into memory
       -m   The maximum resident set size
       -n   The maximum number of open file descriptors (most systems do not allow this
           value to be set)
       -p   The pipe size in 512-byte blocks (this may not be set)
       -q   The maximum number of bytes in POSIX message queues
       -r   The maximum rt priority
       -s   The maximum stack size
       -t   The maximum amount of cpu time in seconds
       -u   The maximum number of processes available to a single user
       -v   The maximum amount of virtual memory available to the shell
       -x   The maximum number of file locks


       If limit is given, it is the new value of the specified resource (the -a option is
       display only). If no option is given, then -f is assumed. Values are in 1024-byte
       increments, except for -t, which is in seconds, -p, which is in units of 512-byte
       blocks, and -n and -u, which are unscaled values. The return status is 0 unless an
       invalid option or argument is supplied, or an error occurs while setting a new limit.


    umask [-p] [-S] [mode]
       The user file-creation mask is set to mode. If mode begins with a digit, it is
       interpreted as an octal number; otherwise it is interpreted as a symbolic mode mask
       similar to that accepted by chmod(1). If mode is omitted, the current value of the
       mask is printed. The -S option causes the mask to be printed in symbolic form; the
       default output is an octal number. If the -p option is supplied, and mode is omit-
       ted, the output is in a form that may be reused as input. The return status is 0 if
       the mode was successfully changed or if no mode argument was supplied, and false oth-
       erwise.


    unalias [-a] [name ...]
       Remove each name from the list of defined aliases. If -a is supplied, all alias def-
       initions are removed. The return value is true unless a supplied name is not a
       defined alias.


    unset [-fv] [name ...]
       For each name, remove the corresponding variable or function. If no options are sup-
       plied, or the -v option is given, each name refers to a shell variable.  Read-only
       variables may not be unset. If -f is specified, each name refers to a shell func-
       tion, and the function definition is removed. Each unset variable or function is
       removed from the environment passed to subsequent commands. If any of RANDOM, SEC-
       ONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are unset, they lose their spe-
       cial properties, even if they are subsequently reset. The exit status is true unless
       a name is readonly.


    wait [n ...]
       Wait for each specified process and return its termination status. Each n may be a
       process ID or a job specification; if a job spec is given, all processes in that
       job’s pipeline are waited for. If n is not given, all currently active child pro-
       cesses are waited for, and the return status is zero. If n specifies a non-existent
       process or job, the return status is 127. Otherwise, the return status is the exit
       status of the last process or job waited for.


SEE ALSO
    bash(1), sh(1)


GNU Bash-3.0           2004 Apr 20         BASH_BUILTINS(1)
(END)


























man使用帮助


           SUMMARY OF LESS COMMANDS


      Commands marked with * may be preceded by a number, N.
      Notes in parentheses indicate the behavior if N is given.


  h  H         Display this help.
  q   q  Q   Q  ZZ     Exit.
 ---------------------------------------------------------------------------


               MOVING


  e  ^E  j  ^N  CR  *  Forward  one line   (or N lines).
  y  ^Y  k  ^K  ^P  *  Backward one line   (or N lines).
  f  ^F  ^V  SPACE  *  Forward  one window (or N lines).
  b  ^B  ESC-v      *  Backward one window (or N lines).
  z                 *  Forward  one window (and set window to N).
  w                 *  Backward one window (and set window to N).
  ESC-SPACE         *  Forward  one window, but don't stop at end-of-file.
  d  ^D             *  Forward  one half-window (and set half-window to N).
  u  ^U             *  Backward one half-window (and set half-window to N).
  ESC-)  RightArrow *  Left  one half screen width (or N positions).
  ESC-(  LeftArrow  *  Right one half screen width (or N positions).
  F                    Forward forever; like "tail -f".
  r  ^R  ^L            Repaint screen.
  R                    Repaint screen, discarding buffered input.
 ---------------------------------------------------
    Default "window" is the screen height.
    Default "half-window" is half of the screen height.
 ---------------------------------------------------------------------------


              SEARCHING


  /pattern      *  Search forward for (N-th) matching line.
  ?pattern      *  Search backward for (N-th) matching line.
  n             *  Repeat previous search (for N-th occurrence).
  N             *  Repeat previous search in reverse direction.
  ESC-n         *  Repeat previous search, spanning files.
  ESC-N         *  Repeat previous search, reverse dir. & spanning files.
  ESC-u        Undo (toggle) search highlighting.
    ---------------------------------------------------
    Search patterns may be modified by one or more of 
    ^N or !  Search for NON-matching lines.
    ^E or *  Search multiple files (pass thru END OF FILE).
    ^F or @  Start search at FIRST file (for /) or last file (for ?).
    ^K       Highlight matches, but don't move (KEEP position).
    ^R       Don't use REGULAR EXPRESSIONS.
 ---------------------------------------------------------------------------


               JUMPING


  g  <  ESC-<       *  Go to first line in file (or line N).
  G  >  ESC->       *  Go to last line in file (or line N).
  p  %              *  Go to beginning of file (or N percent into file).
  t                 *  Go to the (N-th) next tag.
  T                 *  Go to the (N-th) previous tag.
  {  (  [           *  Find close bracket } ) ].
  }  )  ]           *  Find open bracket { ( [.
  ESC-^F  *  Find close bracket .
  ESC-^B  *  Find open bracket  
    ---------------------------------------------------
    Each "find close bracket" command goes forward to the close bracket 
      matching the (N-th) open bracket in the top line.
    Each "find open bracket" command goes backward to the open bracket 
      matching the (N-th) close bracket in the bottom line.


  m        Mark the current position with .
  '        Go to a previously marked position.
  ''           Go to the previous position.
  ^X^X         Same as '.
    ---------------------------------------------------
    A mark is any upper-case or lower-case letter.
    Certain marks are predefined 
         ^  means  beginning of the file
         $  means  end of the file
 ---------------------------------------------------------------------------


            CHANGING FILES


   e [file]        Examine a new file.
  ^X^V             Same as  e.
   n               *  Examine the (N-th) next file from the command line.
   p               *  Examine the (N-th) previous file from the command line.
   x               *  Examine the first (or N-th) file from the command line.
   d               Delete the current file from the command line list.
  =  ^G   f        Print current file name.
 ---------------------------------------------------------------------------


            MISCELLANEOUS COMMANDS


  -          Toggle a command line option [see OPTIONS below].
  --         Toggle a command line option, by name.
  _          Display the setting of a command line option.
  __         Display the setting of an option, by name.
  +cmd             Execute the less cmd each time a new file is examined.


  !command         Execute the shell command with $SHELL.
  |Xcommand        Pipe file between current pos & mark X to shell command.
  v                Edit the current file with $VISUAL or $EDITOR.
  V                Print version number of "less".
 ---------------------------------------------------------------------------


               OPTIONS


    Most options may be changed either on the command line,
    or from within less by using the - or -- command.
    Options may be given in one of two forms  either a single
    character preceded by a -, or a name preceeded by --.


  -?  ........  --help
          Display help (from command line).
  -a  ........  --search-skip-screen
          Forward search skips current screen.
  -b [N]  ....  --buffers=[N]
          Number of buffers.
  -B  ........  --auto-buffers
          Don't automatically allocate buffers for pipes.
  -c  -C  ....  --clear-screen  --CLEAR-SCREEN
          Repaint by scrolling/clearing.
  -d  ........  --dumb
          Dumb terminal.
  -D [xn.n]  .  --color=xn.n
          Set screen colors. (MS-DOS only)
  -e  -E  ....  --quit-at-eof  --QUIT-AT-EOF
          Quit at end of file.
  -f  ........  --force
          Force open non-regular files.
  -F  ........  --quit-if-one-screen
          Quit if entire file fits on first screen.
  -g  ........  --hilite-search
          Highlight only last match for searches.
  -G  ........  --HILITE-SEARCH
          Don't highlight any matches for searches.
  -h [N]  ....  --max-back-scroll=[N]
          Backward scroll limit.
  -i  ........  --ignore-case
          Ignore case in searches that do not contain uppercase.
  -I  ........  --IGNORE-CASE
          Ignore case in all searches.
  -j [N]  ....  --jump-target=[N]
          Screen position of target lines.
  -J  ........  --status-column
          Display a status column at left edge of screen.
  -k [file]  .  --lesskey-file=[file]
          Use a lesskey file.
  -L  ........  --no-lessopen
          Ignore the LESSOPEN environment variable.
  -m  -M  ....  --long-prompt  --LONG-PROMPT
          Set prompt style.
  -n  -N  ....  --line-numbers  --LINE-NUMBERS
          Use line numbers.
  -o [file]  .  --log-file=[file]
          Copy to log file (standard input only).
  -O [file]  .  --LOG-FILE=[file]
          Copy to log file (unconditionally overwrite).
  -p [pattern]  --pattern=[pattern]
          Start at pattern (from command line).
  -P [prompt]   --prompt=[prompt]
          Define new prompt.
  -q  -Q  ....  --quiet  --QUIET  --silent --SILENT
          Quiet the terminal bell.
  -r  -R  ....  --raw-control-chars  --RAW-CONTROL-CHARS
          Output "raw" control characters.
  -s  ........  --squeeze-blank-lines
          Squeeze multiple blank lines.
  -S  ........  --chop-long-lines
          Chop long lines.
  -t [tag]  ..  --tag=[tag]
          Find a tag.
  -T [tagsfile] --tag-file=[tagsfile]
          Use an alternate tags file.
  -u  -U  ....  --underline-special  --UNDERLINE-SPECIAL
          Change handling of backspaces.
  -V  ........  --version
          Display the version number of "less".
  -w  ........  --hilite-unread
          Highlight first new line after forward-screen.
  -W  ........  --HILITE-UNREAD
          Highlight first new line after any forward movement.
  -x [N[,...]]  --tabs=[N[,...]]
          Set tab stops.
  -X  ........  --no-init
          Don't use termcap init/deinit strings.
        --no-keypad
          Don't use termcap keypad init/deinit strings.
  -y [N]  ....  --max-forw-scroll=[N]
          Forward scroll limit.
  -z [N]  ....  --window=[N]
          Set size of window.
  -" [c[c]]  .  --quotes=[c[c]]
          Set shell quote characters.
  -~  ........  --tilde
          Don't display tildes after end of file.
  -# [N]  ....  --shift=[N]
          Horizontal scroll amount (0 = one half screen width)


 ---------------------------------------------------------------------------


              LINE EDITING


    These keys can be used to edit text being entered 
    on the "command line" at the bottom of the screen.


 RightArrow       ESC-l     Move cursor right one character.
 LeftArrow        ESC-h     Move cursor left one character.
 CNTL-RightArrow  ESC-RightArrow  ESC-w     Move cursor right one word.
 CNTL-LeftArrow   ESC-LeftArrow   ESC-b     Move cursor left one word.
 HOME             ESC-0     Move cursor to start of line.
 END              ESC-$     Move cursor to end of line.
 BACKSPACE                  Delete char to left of cursor.
 DELETE           ESC-x     Delete char under cursor.
 CNTL-BACKSPACE   ESC-BACKSPACE         Delete word to left of cursor.
 CNTL-DELETE      ESC-DELETE      ESC-X     Delete word under cursor.
 CNTL-U           ESC (MS-DOS only)     Delete entire line.
 UpArrow          ESC-k     Retrieve previous command line.
 DownArrow        ESC-j     Retrieve next command line.
 TAB                        Complete filename & cycle.
 SHIFT-TAB        ESC-TAB   Complete filename & reverse cycle.
 CNTL-L                     Complete filename, list all.




















File  info.info,  Node  Help,  Next  Help-P,  Prev  Help-Small-Screen,  Up  Getting Started


1.2 How to use Info
===================


You are talking to the program Info, for reading documentation.


   There are two ways to use Info  from within Emacs or as a
stand-alone reader that you can invoke from a shell using the command
`info'.


   Right now you are looking at one "Node" of Information.  A node
contains text describing a specific topic at a specific level of
detail.  This node's topic is "how to use Info".  The mode line says
that this is node `Help' in the file `info'.


   The top line of a node is its "header".  This node's header (look at
it now) says that the `Next' node after this one is the node called
`Help-P'.  An advanced Info command lets you go to any node whose name
you know.  In the stand-alone Info reader program, the header line
shows the names of this node and the info file as well.  In Emacs, the
header line is duplicated in a special typeface, and the duplicate
remains at the top of the window all the time even if you scroll
through the node.


   Besides a `Next', a node can have a `Previous' link, or an `Up'
link, or both.  As you can see, this node has all of these links.


   Now it is time to move on to the `Next' node, named `Help-P'.


>> Type `n' to move there.  Type just one character;
   do not type the quotes and do not type a afterward.


`>>' in the margin means it is really time to try a command.


>> If you are in Emacs and have a mouse, and if you already practiced
   typing `n' to get to the next node, click now with the middle
   mouse button on the `Next' link to do the same "the mouse way".