Linux常用命令笔记---shell编程基础

查看所有的Shell变量：[root@szm ~]# set

查看所有预定义Shell变量：[root@szm ~]# env

定义一个Shell变量： [root@szm ~]# VAR1="test"

[root@szm ~]# set | grep VAR1

VAR1=test

 

删除一个变量： [root@szm ~]# set | grep VAR1

_=VAR1

 

BASH=/bin/bash

HISTFILE=/root/.bash_history

LANG=en_US.UTF-8

PATH=/usr/Kerberos/sbin:/usr/Kerberos/bin:

SHELL=/bin/bash

UID=0

 

Shell变量赋值：不用加$，引用变量时要加$

 

输出命令：printf    echo

 

[root@szm bash]# cat mysc.sh 

#!/bin/bash

V1="abcdef"

V2=8888

V3=8

 

printf "%s\t%d" $V1 $V2

[root@szm bash]# . mysc.sh 

abcdef 8888[root@szm bash]# 

 

 

%d：整数 %s：字符串 \n：回车换行 \r：只回车 \t：水平制表符 \v：垂直制表符

 

运算：

1）表达式必须置于$[]内
2）数字与运算符之间应当有一个空格

[root@szm bash]# cat a1.sh 

#!/bin/bash

a=$[ 3+2 ]

echo "a="$a

b=$[ 3+2*25/3-1 ]

echo "b="$b

-gt：大于 -lt：小于 -eq：等于 -ne：不等于 -ge：大于等于 -le：小于等于

 

       -a file   True if file exists.

       -b file   True if file exists and is a block special file.

       -c file   True if file exists and is a character special file.

       -d file   True if file exists and is a directory.

       -e file   True if file exists.

       -f file   True if file exists and is a regular file.

       -g file   True if file exists and is set-group-id.

       -h file   True if file exists and is a symbolic link.

       -k file   True if file exists and its ‘‘sticky’’ bit is set.

       -p file   True if file exists and is a named pipe (FIFO).

       -r file              True if file exists and is readable.

       -s file   True if file exists and has a size greater than zero.

       -t fd     True if file descriptor fd is open and refers to a terminal.

       -u file   True if file exists and its set-user-id bit is set.

       -w file   True if file exists and is writable.

       -x file   True if file exists and is executable.

       -O file   True if file exists and is owned by the effective user id.

       -G file   True if file exists and is owned by the effective group id.

       -L file   True if file exists and is a symbolic link.

       -S file   True if file exists and is a socket.

       -N file   True if file exists and has been modified since it was last read.

       file1 -nt file2    True if file1 is newer (according to modification date) than file2, or if file1 exists  and file2 does not.

       file1 -ot file2

              True if file1 is older than file2, or if file2 exists and file1 does not.

       file1 -ef file2

              True if file1 and file2 refer to the same device and inode numbers.

 

控制流：

 

if[];then

    .....

fi

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

if[];then

   .....

else

   .....

fi

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

if[];then

    .....

elif[];then

   .....

elif[];then

   ....

if

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

==========================================================

case .... in

    ..)

    .....

;;

    ..)

    .....

;;

    *)

    ....

esac

==========================================================

for ... in ...

do

   ......

done

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

while []

do

   .....

done

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

until []

do

  .....

cone

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

 

函数的定义与使用：

 

function ....()

{

    .....

}

 

包含功能（包含另一个Shell脚本）：

. 文件名