我使用过的Linux命令之for - Bash中的For循环

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用途说明

在shell中用于循环。类似于其他编程语言中的for，但又有些不同。for循环是Bash中最常用的语法结构。

常用格式

格式一

for 变量

do

语句

done

格式二

for 变量 in 列表

do

语句

done

格式三

for ((变量=初始值; 条件判断; 变量变化))

do

语句

done

使用示例

示例一

Bash代码


for s in ac apropos at arp

do

echo $s

done

[root@jfht ~]# for s in ac apropos at arp

> do

> echo $s

> done

ac

apropos

at

arp

[root@jfht ~]#

示例二

Bash代码


for f in *

do

echo $f

done

[root@jfht ~]# for f in *

> do

> echo $f

> done

anaconda-ks.cfg

bak181

hlx

install.log

install.log.syslog

job.sh

job.txt

mbox

mini

setup

temp

vsftpd-2.0.5-16.el5.i386.rpm

vsftpd.conf

work191

[root@jfht ~]#

示例三

Bash代码


ls >ls.txt

for s in $(cat ls.txt)

do

echo $s

done

[root@jfht ~]# ls >ls.txt

[root@jfht ~]# for s in $(cat ls.txt)

>

> do

>

> echo $s

>

> done

anaconda-ks.cfg

bak181

hlx

install.log

install.log.syslog

job.sh

job.txt

ls.txt

mbox

mini

setup

temp

vsftpd-2.0.5-16.el5.i386.rpm

vsftpd.conf

work191

[root@jfht ~]#

示例四

Bash代码


print_args()

{

for arg in "$@"

do

echo $arg

done

}

print_args 1 2 3 4

print_args "this is a test"

<span style="color: #000000;">print_args this is a test</span>

[root@smsgw root]# print_args()

> {

> for arg in "$@"

> do

> echo $arg

> done

> }

[root@smsgw root]# print_args 1 2 3 4

1

2

3

4

[root@smsgw root]# print_args "this is a test"

this is a test

[root@smsgw root]# print_args this is a test

this

is

a

test

示例五

Bash代码


for ((i=0; i<10; ++i))

do

echo $i

done

[root@smsgw root]# for ((i=0; i<10; ++i))

> do

> echo $i

> done

0

1

2

3

4

5

6

7

8

9

示例六 列表为数组

Bash代码


AREAS=(1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913)

NAMES=(南京 无锡 徐州 常州 苏州 南通 连云港 淮安 盐城 扬州 镇江 泰州 宿迁)

NUM_OF_AREAS=13

area_name_of()

{

for ((I=0; I<$NUM_OF_AREAS; ++I))

do

if [ "$1" == "${AREAS[I]}" ]; then

echo "${NAMES[I]}"

fi

done

}

echo $(area_name_of 1903)

for AREA in ${AREAS[*]};

do

echo $AREA $(area_name_of $AREA)

done

[root@smsgw root]# AREAS=(1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913)

[root@smsgw root]# NAMES=(南京 无锡 徐州 常州 苏州 南通 连云港 淮安 盐城 扬州 镇江 泰州 宿迁)

[root@smsgw root]# NUM_OF_AREAS=13

[root@smsgw root]# area_name_of()

> {

> for ((I=0; I<$NUM_OF_AREAS; ++I))

> do

> if [ "$1" == "${AREAS[I]}" ]; then

> echo "${NAMES[I]}"

> fi

> done

> }

[root@smsgw root]# echo $(area_name_of 1903)

徐州

[root@smsgw root]# for AREA in ${AREAS[*]};

> do

> echo $AREA $(area_name_of $AREA)

> done

1901 南京

1902 无锡

1903 徐州

1904 常州

1905 苏州

1906 南通

1907 连云港

1908 淮安

1909 盐城

1910 扬州

1911 镇江

1912 泰州

1913 宿迁

[root@smsgw root]#

示例七 bash version 3.0+

Java代码


bash --version

for i in {1..5}

do

echo "Welcome $i times"

done

[root@smsgw root]# bash --version

GNU bash, version 2.05b.0(1)-release (i386-redhat-linux-gnu)

Copyright (C) 2002 Free Software Foundation, Inc.

[root@smsgw root]# for i in {1..5}

> do

> echo "Welcome $i times"

> done

Welcome {1..5} times

[root@smsgw root]#

换个较高版本的Linux。

[root@jfht ~]# bash --version

GNU bash, version 3.2.25(1)-release (i686-redhat-linux-gnu)

Copyright (C) 2005 Free Software Foundation, Inc.

[root@jfht ~]# for i in {1..5}

> do

> echo "Welcome $i times"

> done

Welcome 1 times

Welcome 2 times

Welcome 3 times

Welcome 4 times

Welcome 5 times

[root@jfht ~]#

示例八 Bash v4.0+

Bash代码


echo "Bash version ${BASH_VERSION}..."

for i in {0..10..2}

do

echo "Welcome $i times"

done

[root@smsgw root]# echo "Bash version ${BASH_VERSION}..."

Bash version 2.05b.0(1)-release...

[root@smsgw root]# for i in {0..10..2}

> do

> echo "Welcome $i times"

> done

Welcome {0..10..2} times

[root@smsgw root]#

换个较高版本的Linux。

[root@jfht ~]# echo "Bash version ${BASH_VERSION}..."

Bash version 3.2.25(1)-release...

[root@jfht ~]# for i in {0..10..2}

> do

> echo "Welcome $i times"

> done

Welcome {0..10..2} times

[root@jfht ~]#

传说Bash4.0可以支持这种语法。

Bash version 4.0.33(0)-release...

Welcome 0 times

Welcome 2 times

Welcome 4 times

Welcome 6 times

Welcome 8 times

Welcome 10 times