Bash Shell Cheatsheet

本文记下常用的bash shell语法和命令，方便日后参考。

参考文档

Bash Guide for Beginners
http://www.tldp.org/LDP/Bash-Beginners-Guide/html/

注释 Comment

1. bash脚本要以

#!/bin/bash 

开头。
2. ‘#’号后面的都是注释，如

# An example for bash comment.
echo "hehe"    # Print hehe to screen.

运行脚本 Run Script

1. 以Bash子进程运行，环境变量依然有效；（需要执行权限）

$ ./test.sh

或者

$ bash test.sh

开启调试模式

$ bash -x test.sh

2. 直接在当前Bash运行，环境变量和当前Bash的变量都有效；

$ source test.sh

或者

$ . test.sh

变量 Variables

定义变量可以很简单

var1 = hehe
var2 = 20
var3 = 6.1

如果想bash的子进程也能使用该变量，要加一个export.

export globle_var1 = 20

字符引用：单引号
单引号引用的所有字符都会escaped。

echo '$date'
$date

字符引用：双引号
双引号会escaped除了$符，反引号，\的字符

franky ~> echo "$date"
20021226

franky ~> echo "`date`"
Sun Apr 20 11:22:06 CEST 2003

franky ~> echo "I'd say: \"Go for it!\""
I'd say: "Go for it!"

franky ~> echo "\"
More input>"

franky ~> echo "\\"
\

常用变量

1. $# 输入的参数个数；
2. $? 上条命令的退出值；
3. $0 shell文件名；

输入输出 IO

1. 输出 echo

$ echo test
test

2. 输出 printf

$ printf "%d\n" 100000

3. 输入 read

read var1 var2... 

条件控制 Condition Control

if

http://www.tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html
if语句的语法

if TEST-COMMANDS; then CONSEQUENT-COMMANDS; fi

if TEST-COMMANDS; then

CONSEQUENT-COMMANDS;

elif MORE-TEST-COMMANDS; then

MORE-CONSEQUENT-COMMANDS;

else ALTERNATE-CONSEQUENT-COMMANDS;

fi 

判断大小

if [ "$?" -ne "0" ]

case

case EXPRESSION in CASE1) COMMAND-LIST;; CASE2) COMMAND-LIST;; ... CASEN) COMMAND-LIST;; esac 

示例

case "$1" in
        start)
            start
            ;;
         
        stop)
            stop
            ;;
         
        status)
            status anacron
            ;;
        restart)
            stop
            start
            ;;
        condrestart)
            if test "x`pidof anacron`" != x; then
                stop
                start
            fi
            ;;
         
        *)
            echo $"Usage: $0 {start|stop|restart|condrestart|status}"
            exit 1
 
esac

循环 Loop

for

for NAME [in LIST ]; do COMMANDS; done

Example:

for filename in `ls $1`
do
cmp $1$filename $2$filename
done

for ((i=0; i<1024; i++))
do
commands
done

while

while CONTROL-COMMAND; do CONSEQUENT-COMMANDS; done 

until

until TEST-COMMAND; do CONSEQUENT-COMMANDS; done 

break, continue

break和continue用法跟C语言一样。

正则表达式 Regular expressions

.	Matches any single character.
?	The preceding item is optional and will be matched, at most, once.
*	The preceding item will be matched zero or more times.
+	The preceding item will be matched one or more times.
{N}	The preceding item is matched exactly N times.
{N,}	The preceding item is matched N or more times.
{N,M}	The preceding item is matched at least N times, but not more than M times.
-	represents the range if it's not first or last in a list or the ending point of a range in a list.
^	Matches the empty string at the beginning of a line; also represents the characters not in the range of a list.
$	Matches the empty string at the end of a line.
\b	Matches the empty string at the edge of a word.
\B	Matches the empty string provided it's not at the edge of a word.
\<	Match the empty string at the beginning of word.
\>	Match the empty string at the end of word.

grep要用re的话，最好加上 -E 这个参数；

sed

查看sed的用法： info sed

Command	Result
a\	Append text below current line.
c\	Change text in the current line with new text.
d	Delete text.
i\	Insert text above current line.
p	Print text.
r	Read a file.
s	Search and replace text.
w	Write to a file.

Option	Effect
-e SCRIPT	Add the commands in SCRIPT to the set of commands to be run while processing the input.
-f	Add the commands contained in the file SCRIPT-FILE to the set of commands to be run while processing the input.
-n	Silent mode.
-V	Print version information and exit.

awk

The variables $1, $2, $3, ..., $N hold the values of the first, second, third until the last field of an input line. The variable $0 (zero) holds the value of the entire line.

kelly@octarine ~/test> ls -l | awk '{ print $5 $9 }'
160orig
121script.sed
120temp_file
126test
120twolines
441txt2html.sh

kelly@octarine ~/test> ls -ldh * | grep -v total | \ 
awk '{ print "Size is " $5 " bytes for " $9 }'
Size is 160 bytes for orig
Size is 121 bytes for script.sed
Size is 120 bytes for temp_file
Size is 126 bytes for test
Size is 120 bytes for twolines
Size is 441 bytes for txt2html.sh

kelly@octarine ~> df -h | sort -rnk 5 | head -3 | \ 
awk '{ print "Partition " $6 "\t: " $5 " full!" }'
Partition /var  : 86% full!
Partition /usr  : 85% full!
Partition /home : 70% full!

函数 Function

定义

function FUNCTION { COMMANDS; }
or
FUNCTION () { COMMANDS; } 

参数

function的参数与脚本的参数差不多。

[lydia@cointreau ~/test] cat showparams.sh
#!/bin/bash
                                                                                
echo "This script demonstrates function arguments."
echo
                                                                                
echo "Positional parameter 1 for the script is $1."
echo
                                                                                
test ()
{
echo "Positional parameter 1 in the function is $1."
RETURN_VALUE=$?
echo "The exit code of this function is $RETURN_VALUE."
}
                                                                                
test other_param

[lydia@cointreau ~/test] ./showparams.sh parameter1
This script demonstrates function arguments.
 
Positional parameter 1 for the script is parameter1.
 
Positional parameter 1 in the function is other_param.
The exit code of this function is 0.