Learning Linux
基础知识
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Background Process
CTRL+Z挂起进程并放入后台
jobs 显示当前暂停的进程
bg %N 使第N个任务在后台运行(%前有空格)
fg %N 使第N个任务在前台运行
默认bg,fg不带%N时表示对最后一个进程操作!
kill %N : 杀死第N个后台进程
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Command
bc - An arbitrary precision calculator language
cat - concatenate and print files
cmp - compare two files byte by byte
cut - remove sections from each line of files
# 截取PATH中第3个和第5个，以':'分割
echo ${PATH} | cut -d ':' -f 3,5
# 截取export变量12个字符后的字符串
export | cut -c 12-
# 截取export变量第12个到第20个字符
export | cut -c 12-20df - report file system disk space usage
diff - compare files line by line
du - estimate file space usage
env - run a program in a modified environment
env 显示当前shell的环境变量和自定义变量（不包含父进程未export的自定义变量）
export 显示由父进程共享出来的变量
set 显示所有环境变量、自定义变量、shell自身描述变量file - determine file type
gawk - pattern scanning and processing language
grep, egrep, fgrep - print lines matching a pattern
head - output the first part of files
iconv - 转换给定文件的编码。将繁体字转为简体字示例：
iconv -f utf8 -t big5 vi.utf8 | iconv -f big5 -t gb2312 | iconv -f gb2312 -t utf8 -o vi.gb.utf8id - return user identity
info - read Info documents
less - file reading
locale - display locale settings
locate - find files by name
od - dump files in octal and other formats
> echo abcdefghiklmnopqrstuvwxyz | od -A d -w10 -t xCoCdCc
0000000 61 62 63 64 65 66 67 68 69 6b
141 142 143 144 145 146 147 150 151 153
97 98 99 100 101 102 103 104 105 107
a b c d e f g h i k
0000010 6c 6d 6e 6f 70 71 72 73 74 75
154 155 156 157 160 161 162 163 164 165
108 109 110 111 112 113 114 115 116 117
l m n o p q r s t u
0000020 76 77 78 79 7a 0a
166 167 170 171 172 012
118 119 120 121 122 10
v w x y z \n
0000026rsync - a fast, versatile, remote (and local) file-copying tool
localhost > ls -lrt /tmp/test/
-rw-r--r-- 1 zyd staff 11 4 22 16:15 1.txt
192.168.17.53 > ls -lrt /tmp/test/
-rw-r--r--. 1 root root 2 4月 15 13:09 1.txt
-rw-r--r--. 1 root root 10 4月 22 16:42 2.txt
# 同步两边目录，规则：不覆盖，多删少补；
rsync -v -r --ignore-existing --delete /tmp/test 192.168.17.53:/tmp
192.168.17.53 > ls -lrt /tmp/test/
-rw-r--r--. 1 root root 2 4月 15 13:09 1.txt
# 可以看到：1.txt没有被覆盖；2.txt被删除；
sed - stream editor for filtering and transforming text
sort - sort lines of text files
split - split a file into pieces
stty - set the options for a terminal device interface
tac - concatenate and print files in reverse
tail - output the last part of files
tee - read from standard input and write to standard output and files
test - check file types and compare values
time - calculate execute time
> time ls
bin boot dev etc home lib lib64 lost+found media mnt opt proc root run sbin srv sys tmp usr var
real 0m0.003s
user 0m0.001s
sys 0m0.002str - translate or delete characters
type - query command type
> type -a ls
ls 是 `ls --color=auto' 的别名
ls 是 /usr/bin/lsuname - print system information
uniq - report or omit repeated lines
wc - print newline, word, and byte counts for each file
xargs - build and execute command lines from standard input
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快捷键
Ctrl + D 键盘输入结束（End of file，EOF，End of input）
Ctrl + Z : 将任务中断,但是此任务并没有结束,他仍然在进程中他只是维持挂起的状态，可以使用fg/bg操作继续前台或后台任务。
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Help
man
info
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需要注意的点
- 双引号和单引号的区别：
> name=zyd
> myname='my name is ${name}'
> echo ${myname}
my name is ${name}
> myname="my name is ${name}"
> echo ${myname}
my name is zyd网络方面
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使用nc测两台机子udp连通性
A：nc -vul 12121
B：nc -vu A 12121现在A 和 B能互相通信