shell脚本学习之循环语句

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for循环语句格式

for var in （表达式）
do
    Command
done

实例：计算1-100和

#!/bin/bash
sum=0
for i in `seq 1 100`
do
  sum=$(expr $sum + $i)
done
echo $sum

[root@jiangpeisi shell]# sh for.sh 
5050

while循环语句格式

while（表达式）
do
    command
done

实例：循环按行打印文件内容

#!/bin/bash
while read line
do
   echo $line
done < /root/shell/a.txt

[root@jiangpeisi shell]# sh while.sh 
lkitd:x:998:997:User for polkitd:/:/sbin/nologin
tss:x:59:59:Account used by the trousers package to sandbox the tcsd daemon:/dev/null:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologin
chrony:x:997:995::/var/lib/chrony:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
nscd:x:28:28:NSCD Daemon:/:/sbin/nologin
tcpdump:x:72:72::/:/sbin/nologin
admin:x:1000:1000::/home/admin:/bin/bash
dockerroot:x:996:993:Docker User:/var/lib/docker:/sbin/nologin
dockerroot-latest:x:995:992:Docker User:/var/lib/docker-latest:/sbin/nologin
zarafa:x:994:991:Zarafa Service Account:/var/lib/zarafa:/sbin/nologin
test1:x:1002:1002::/home/test1:/bin/bash
jiangpeisi:x:1004:1004::/home/jiangpeisi:/bin/bash
ftpuser1:x:1005:1005::/home/ftpuser1:/bin/bash
named:x:25:25:Named:/var/named:/bin/false
dhcpd:x:177:177:DHCP server:/:/sbin/nologin
mysql:x:27:27:MariaDB Server:/var/lib/mysql:/sbin/nologin
saslauth:x:993:76:Saslauthd user:/run/saslauthd:/sbin/nologin
apache:x:48:48:Apache:/usr/share/httpd:/sbin/nologin