20.10 for循环
语法:for 变量名 in 条件; do …; done
#!/bin/bash
for i in `seq 1 100`
do
echo $i
done
案例1
#!/bin/bash
sum=0
for i in `seq 1 100`
do
sum=$[$sum+$i]
echo $i
done
echo $sum
[root@aiker02 script]# !vim
vim for0.sh
echo $i
#!/bin/bash
sum=0
for i in `seq 1 100`
do
sum=$[$sum+$i]
done
echo $sum
"for0.sh" 7L, 73C written
[root@aiker02 script]# sh -x !$
sh -x for0.sh
+ echo 5050
5050
[root@aiker02 script]# cat !$
cat for0.sh
#!/bin/bash
sum=0
for i in `seq 1 100`
do
echo "$sum+$i"
sum=$[$sum+$i]
echo $sum
done
[root@aiker02 script]# !v
vim for1.sh
#!/bin/bash
cd /etc/
for a in `ls /etc`
do
[ -d $a ] && ls $a
if [ -d $a ]
then
echo $a
echo "`pwd`/$a"
ls $a
fi
done
[root@aiker02 script]# for i in `seq 1 3`; do echo $i; done
1
2
3
[root@aiker02 script]# for i in 1 2 3; do echo $i; done
1
2
3
注意for在遍历目录时会把空格或者回车作为分隔符
[root@aiker02 script]# ll
total 64
-rw-r--r-- 1 root root 0 Apr 15 16:27 1
-rw-r--r-- 1 root root 0 Apr 15 16:27 2
-rw-r--r-- 1 root root 0 Apr 15 16:27 3 4.txt
[root@aiker02 script]# mkdir textdir
[root@aiker02 script]# mv 1 2 3\ 4.txt textdir/
1234.txt
[root@aiker02 script]# for i in `ls ./textdir`; do echo $i; done
1
2
3
4.txt
[root@aiker02 script]# for i in `ls ./textdir`; do printf "$i\n"; done
1
2
3
4.txt
通常情况下 shell 变量调用需要加 $,但是 for 的 (()) 中不需要,下面来看一个例子:
#!/bin/bash
for((i=1;i<=5;i++));do
echo "这是第 $i 次调用";
done;
与 C 中相似,赋值和下一步执行可以放到代码之前循环语句之中执行,这里要注意一点:如果要在循环体中进行 for 中的 next 操作,记得变量要加 $,不然程序会变成死循环。
20.11/20.12 while循环
语法 while 条件; do … ; done
案例1
#!/bin/bash
while : ##:相当于true,可以使用while true
do
load=`w|head -1|awk -F 'load average: ' '{print $2}'|cut -d. -f1`
if [ $load -gt 10 ]
then
/bin/mail.py [email protected] "load is high" $load
fi
sleep 30
done
[root@aiker02 script]# sh -x while0.sh
+ :
++ head -1
++ awk -F 'load average: ' '{print $2}'
++ cut -d. -f1
++ w
+ load=0
+ '[' 0 -gt 10 ']'
+ sleep 30
+ :
++ head -1
++ awk -F 'load average: ' '{print $2}'
++ cut -d. -f1
++ w
+ load=0
+ '[' 0 -gt 10 ']'
+ sleep 30
+ :
++ head -1
++ awk -F 'load average: ' '{print $2}'
++ cut -d. -f1
++ w
+ load=0
+ '[' 0 -gt 10 ']'
+ sleep 30
^C
while循环: 格式:
while command
do
command
command
command
...
done
[root@aiker02 script]# !vim
vim while1.sh
#!/bin/bash
while :
do
read -p "please input a number:" n
if [ -z $n ]
then
echo 'You need input a string.'
continue
fi
n1=`echo $n | sed 's/[0-9]//g'`
if [ -n "$n1" ]
then
echo "You must input numbers"
continue
fi
break
done
echo $n
[root@aiker02 script]# !sh
sh -x while1.sh
+ :
+ read -p 'please input a number:' n
please input a number:12323
+ '[' -z 12323 ']'
++ sed 's/[0-9]//g'
++ echo 12323
+ n1=
+ '[' -n '' ']'
+ break
+ echo 12323
12323
[root@aiker02 script]# !vim
vim while2.sh
#!/bin/bash
i=1
while [ $i -le 5 ]
do sq=`expr $i \* $i`
echo $i $i的平方是 $sq
i=`expr $i + 1`
done
echo "Job is done."
[root@aiker02 script]# sh !$
sh while2.sh
1 1的平方是 1
2 2的平方是 4
3 3的平方是 9
4 4的平方是 16
5 5的平方是 25
Job is done.
20.13 break跳出循环
• 从循环中退出: break和continue命令 break 立即退出循环 continue 忽略本循环中的其他命令,继续下一下循环 在shell编程中有时我们要用到进行无限循环的技巧,也就是说这种循环一直执行碰 到break或continue命令。这种无限循环通常是使用true或false命令开始的。UNIX 系统中的true总是返0值,而false则返回非零值。如下所示
while true until false
do do
command command
.... ....
command command
done done
break命令允许跳出所有循环(终止执行后面的所有循环)
[root@aiker02 script]# vim break.sh
#!/bin/bash
for i in `seq 1 5`
do
echo $i
if [ $i -eq 3 ]
then
break
fi
echo $i
done
echo "job is done"
[root@aiker02 script]# sh break.sh
1
1
2
2
3
job is done
[root@aiker02 script]# sh -x break.sh
++ seq 1 5
+ for i in '`seq 1 5`'
+ echo 1
1
+ '[' 1 -eq 3 ']'
+ echo 1
1
+ for i in '`seq 1 5`'
+ echo 2
2
+ '[' 2 -eq 3 ']'
+ echo 2
2
+ for i in '`seq 1 5`'
+ echo 3
3
+ '[' 3 -eq 3 ']'
+ break
+ echo 'job is done'
job is done
20.14 continue结束本次循环
忽略continue之下的代码,直接进行下一次循环
continue命令与break命令类似,只有一点差别,它不会跳出所有循环,仅仅跳出当前循环
[root@aiker02 script]# vim continue.sh
#!/bin/bash
for i in `seq 1 5`
do
echo $i
if [ $i -eq 3 ]
then
continue
fi
echo $i
done
echo "job is done"
[root@aiker02 script]# sh continue.sh
1
1
2
2
3
4
4
5
5
job is done
20.15 exit退出整个脚本
[root@aiker02 script]# cp continue.sh exit.sh
[root@aiker02 script]# vim !$
vim exit.sh
#!/bin/bash
for i in `seq 1 5`
do
echo $i
if [ $i -eq 3 ]
then
exit
fi
echo $i
done
echo "job is done"
[root@aiker02 script]# sh exit.sh
1
1
2
2
3
[root@aiker02 script]# !vim
vim exit.sh
#!/bin/bash
for i in `seq 1 5`
do
echo $i
if [ $i -eq 3 ]
then
exit 2
fi
echo $i
done
echo "job is done"
[root@aiker02 script]# sh exit.sh
1
1
2
2
3
[root@aiker02 script]# echo $?
2
扩展
select用法 http://www.apelearn.com/bbs/thread-7950-1-1.html
select也是循环的一种,它比较适合用在用户选择的情况下。
比如,我们有一个这样的需求,运行脚本后,让用户去选择数字,选择1,会运行w命令,选择2运行top命令,选择3运行free命令,选择4退出。脚本这样实现:
#!/bin/bash
echo "Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit"
echo
select command in w top free quit
do
case $command in
w)
w
;;
top)
top
;;
free)
free
;;
quit)
exit
;;
*)
echo "Please input a number:(1-4)."
;;
esac
done
执行结果如下:
sh select.sh
Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit
1) w
2) top
3) free
4) quit
#? 1
16:03:40 up 32 days, 2:42, 1 user, load average: 0.01, 0.08, 0.08
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root pts/0 61.135.172.68 15:33 0.00s 0.02s 0.00s sh select.sh
#? 3
total used free shared buffers cached
Mem: 1020328 943736 76592 0 86840 263624
-/+ buffers/cache: 593272 427056
Swap: 2097144 44196 2052948
#?
我们发现,select会默认把序号对应的命令列出来,每次输入一个数字,则会执行相应的命令,命令执行完后并不会退出脚本。它还会继续让我们再次输如序号。序号前面的提示符,我们也是可以修改的,利用变量PS3即可,再次修改脚本如下:
#!/bin/bash
PS3="Please select a number: "
echo "Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit"
echo
select command in w top free quit
do
case $command in
w)
w
;;
top)
top
;;
free)
free
;;
quit)
exit
;;
*)
echo "Please input a number:(1-4)."
esac
done
如果想要脚本每次输入一个序号后就自动退出,则需要再次更改脚本如下:
#!/bin/bash
PS3="Please select a number: "
echo "Please chose a number, 1: run w, 2: run top, 3: run free, 4: quit"
echo
select command in w top free quit
do
case $command in
w)
w;exit
;;
top)
top;exit
;;
free)
free;exit
;;
quit)
exit
;;
*)
echo "Please input a number:(1-4).";exit
esac
done