shell笔记之控制结构
shell笔记之控制结构
shell笔记之控制结构
if 语句:
Shell代码
#!/bin/bash
www.2cto.com
# if 语句格式:
# if 和then放在不同行,并使else和结束处必须的fi与它们水平对齐
if [ "${1}" = '' ]
then
echo no argument input .
else
echo first argument is : $1
fi
var=2
echo "${var}"
if [ "${var}" = "1" ]
then
echo one .
elif [ "${var}" = "2" ]
then
echo two .
elif [ "${var}" = "3" ]
then
echo three .
else
echo at least four .
fi
for循环:
Shell代码
#!/bin/bash
# in 关键字后面是字列表,
for x in one two three four
do
echo number $x
done
for var in "$@"
do
echo you pass in $var
done
# 使用文件通配符
for myfile in /etc/r*
do
if [ -d "$myfile" ]
then
echo "$myfile is dir"
else
echo "$myfile"
fi
done
# 还可以在字列表中使用多个通配符,甚至是变量
# 可以使用相对路径或绝对路径;对于相对路径,bash是相对于当前工作目录执行通配符扩展。 www.2cto.com
for x in ./* var/lo* /home/${USER}/*
do
echo $x
done
while和until 循环:
Shell代码
#!/bin/bash
echo use while loop control .
myvar=0
while [ $myvar -ne 10 ]
do
echo $myvar
myvar=$(( $myvar + 1 ))
done
www.2cto.com
echo
echo
echo use until loop control .
myvar=10
until [ $myvar -eq 0 ]
do
echo $myvar
myvar=$(( $myvar - 1 ))
done
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