Linux命令For循环
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
# for s in ac apropos at arp
> do
> echo $s
> done
ac
apropos
at
arp
#
示例二
Bash代码
[*] for f in *
[*] do
[*] echo $f
[*] done
# 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
#
示例三
Bash代码
[*] ls >ls.txt
[*] for s in $(cat ls.txt)
[*] do
[*] echo $s
[*] done
# ls >ls.txt
# for s in $(cat ls.txt)
>
> do
>
> echo $s
>
> done
anaconda-ks.cfg
bak181
hlx
install.log
install.log.syslog
job.sh
job.txt
ls.txt
mbox
mini
setup
temp
vsftpd-2.0.5-16.el5.i386.rpm
vsftpd.conf
work191
#
示例四
Bash代码
[*] print_args()
[*] {
[*] for arg in "$@"
[*] do
[*] echo $arg
[*] done
[*] }
[*] print_args 1 2 3 4
[*] print_args "this is a test"
[*] "color: #000000;">print_args this is a test
# print_args()
> {
> for arg in "$@"
> do
> echo $arg
> done
> }
# print_args 1 2 3 4
1
2
3
4
# print_args "this is a test"
this is a test
# print_args this is a test
this
is
a
test
示例五
Bash代码
[*] for ((i=0; i<</span>10; ++i))
[*] do
[*] echo $i
[*] done
# 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}" ]; then
[*] echo "${NAMES}"
[*] fi
[*] done
[*] }
[*] echo $(area_name_of 1903)
[*] for AREA in ${AREAS
[*]};
[*] do
[*] echo $AREA $(area_name_of $AREA)
[*] done
# AREAS=(1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913)
# NAMES=(南京 无锡 徐州 常州 苏州 南通 连云港 淮安 盐城 扬州 镇江 泰州 宿迁)
# NUM_OF_AREAS=13
# area_name_of()
> {
> for ((I=0; I<$NUM_OF_AREAS; ++I))
> do
> if [ "$1" == "${AREAS}" ]; then
> echo "${NAMES}"
> fi
> done
> }
# echo $(area_name_of 1903)
徐州
# 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
#
示例七 bash version 3.0+
Java代码
[*] bash --version
[*] for i in {1..5}
[*] do
[*] echo "Welcome $i times"
[*] done
# bash --version
GNU bash, version 2.05b.0(1)-release (i386-redhat-linux-gnu)
Copyright (C) 2002 Free Software Foundation, Inc.
# for i in {1..5}
> do
> echo "Welcome $i times"
> done
Welcome {1..5} times
#
换个较高版本的Linux。
# bash --version
GNU bash, version 3.2.25(1)-release (i686-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.
# 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
#
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
# echo "Bash version ${BASH_VERSION}..."
Bash version 2.05b.0(1)-release...
# for i in {0..10..2}
> do
> echo "Welcome $i times"
>done
Welcome {0..10..2} times
#
换个较高版本的Linux。
# echo "Bash version ${BASH_VERSION}..."
Bash version 3.2.25(1)-release...
# for i in {0..10..2}
> do
> echo "Welcome $i times"
>done
Welcome {0..10..2} times
#
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
问题思考
1. 怎么用for实现死循环（无限循环）？
2. 比较几种写法的不同：(1) for arg in $* (2) for arg in $@ (3) for arg in "$*" (4) for arg in "$@"
3. 怎么跳出for循环？
4. for s; do echo $s; done这个写法的执行结果是什么？
相关资料
【1】小蜗牛技术之家 BASH for 循环小结
【2】相当不错的介绍for语句的英文资料 Bash For Loop Examples
【3】Bash新手指南 第9章 重复性任务
【4】Keep IT Simple and Stupid 在Bash的命令行使用For循环
页:
[1]