shell循环示例

for循环示例

for循环语法：

1	for VARIABLE in 1 2 3 4 5 .. N

2

do

3

command1

4

command2

5

commandN

6

done

 

01	#!/bin/bash

02

03	for i in 1 2 3 4 5

04

05

do

06

07	echo "Welcome $i times"

08

09

done

10

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