本文总结Linux bash的常见用法，作为Cheat sheet使用。
第一行!#/bin/bash为释伴(shebang)
#!/bin/bash
cp $1 $2
echo "Copy done"
$0为文件名$1-$9为参数$#为参数量$$当前bash进程ID$USER$HOSTNAME$PATH，用:间隔r'...'#!/bin/bash
dir=../
ls $dir
var=Hello World
# -bash: World: command not found
var='Hello World'
echo $var # Hello World
newvar='More $var'
echo $newvar # More $var
newvar="More $var"
echo $newvar # More Hello World
因此如果要在多条指令中传多个同样的参数，那么可以用单引号括起来声明变量后传入。
用$(...)进行书写，括号里内容会直接执行
myvar=$( ls /etc )
echo $myvar
# Documents Desktop ...
如果变量需要在另外的bash文件中用，则需通过export导出
#!/bin/bash
# demonstrate variable scope 1.
var1=blah
export var1
./script2.sh
用let <expr>语句或者$((...))
#!/bin/bash
let "a = 5 + 4"
echo $a # 9
let "a = $1 + 30"
echo $a # 30 + first command line argument
b=$(( $a + 3 ))
echo $b
#!/bin/bash
# Basic if statement
if [ $1 -gt 100 ]
then
echo Hey that\'s a large number.
pwd
fi
date
| Operator | Description |
|---|---|
| ! EXPRESSION | The EXPRESSION is false. |
| -n STRING | The length of STRING is greater than zero. |
| -z STRING | The lengh of STRING is zero (ie it is empty). |
| STRING1 = STRING2 | STRING1 is equal to STRING2 |
| STRING1 != STRING2 | STRING1 is not equal to STRING2 |
| INTEGER1 -eq INTEGER2 | INTEGER1 is numerically equal to INTEGER2 |
| INTEGER1 -gt INTEGER2 | INTEGER1 is numerically greater than INTEGER2 |
| INTEGER1 -lt INTEGER2 | INTEGER1 is numerically less than INTEGER2 |
| -d FILE | FILE exists and is a directory. |
| -e FILE | FILE exists. |
| -r FILE | FILE exists and the read permission is granted. |
| -s FILE | FILE exists and it’s size is greater than zero (ie. it is not empty). |
| -w FILE | FILE exists and the write permission is granted. |
| -x FILE | FILE exists and the execute permission is granted. |
| or - |
#!/bin/bash
# case example
case $1 in
start) # pattern 1
echo starting
;; # needed!
stop)
echo stoping
;;
restart)
echo restarting
;;
*)
echo don\'t know
;;
esac # needed!
#!/bin/bash
# Basic while loop
counter=1
while [ $counter -le 10 ]
do
echo $counter
((counter++))
done
names='Stan Kyle Cartman'
for name in $names
do
echo $name
done
for value in {1..5}
do
echo $value
done
echo "All done"
# & means run in backstage
# nohup means not stopping running after the terminal is dead
# > means redirect output to file
$ nohup ./run.sh > out.log &
# show output on the screen and also output to file
$ ./run.sh | tee out.log
# https://stackoverflow.com/questions/6674327/redirect-all-output-to-file-in-bash
# The > operator redirects the output usually to a file but it can be to a device. You can also use >> to append.
# > file redirects stdout to file
# 1> file redirects stdout to file
# 2> file redirects stderr to file
# &> file redirects stdout and stderr to file
# /dev/null is the null device it takes any input you want and throws it away. It can be used to suppress any output.
$ ./run.sh > out.log 2>&1
# run the program for 10s
$ timeout 10 top
# list all programs
ps -fu username