linux shell循环示例
for循环示例
for循环语法：
for VARIABLE in 1 2 3 4 5 .. N
do
command1
command2
commandN
done
#!/bin/bash for i in 1 2 3 4 5 do echo "Welcome $i times" done
bash version 3.0+版本
#!/bin/bash
for i in {1..5}
do
echo "Welcome $i times"
done
bash version 4版本
#!/bin/bash
echo "Bash version ${BASH_VERSION}..."
for i in {0..10..2}
do
echo "Welcome $i times"
done
含有“seq”命令的语法示例
#!/bin/bash
for i in $(seq 1 2 20)
do
echo "Welcome $i times"
done
for循环的三个表达式
语法如下：
for (( EXP1; EXP2; EXP3 ))
do
command1
command2
command3
done
示例如下：
#!/bin/bash
for (( c=1; c<=5; c++ ))
do
echo "Welcome $c times..."
done
效果：
Welcome 1 times Welcome 2 times Welcome 3 times Welcome 4 times Welcome 5 times
for的无限循环
#!/bin/bash
for (( ; ; ))
do
echo "infinite loops [ hit CTRL+C to stop]"
done
break条件语句
for I in 1 2 3 4 5
do
statements1 #Executed for all values of ''I'', up to a disaster-condition if any.
statements2
if (disaster-condition)
then
break #Abandon the loop.
fi
statements3 #While good and, no disaster-condition.
done
下面的shell脚本将通过在/ etc目录中存储的所有文件。 for循环将放弃当/ etc / resolv.conf的文件中找到。
#!/bin/bash
for file in /etc/*
do
if [ "${file}" == "/etc/resolv.conf" ]
then
countNameservers=$(grep -c nameserver /etc/resolv.conf)
echo "Total ${countNameservers} nameservers defined in ${file}"
break
fi
done
continue条件语句
for I in 1 2 3 4 5
do
statements1 #Executed for all values of ''I'', up to a disaster-condition if any.
statements2
if (condition)
then
continue #Go to next iteration of I in the loop and skip statements3
fi
statements3
done
利用这个脚本在命令行中指定的所有文件名的备份。如果。bak文件存在，它会跳过cp命令。
#!/bin/bash
FILES="$@"
for f in $FILES
do
# if .bak backup file exists, read next file
if [ -f ${f}.bak ]
then
echo "Skiping $f file..."
continue # read next file and skip cp command
fi
# we are hear means no backup file exists, just use cp command to copy file
/bin/cp $f $f.bak
done