条件判断

条件判断

单分支的if语句
if 判断条件；then
  statement1
  statement2
  ....
fi

双分支的if语句
if 判断条件；then
  statement1
  statement2
else
  statement3
  ....
fi

如

#!/bin/bash
name=ylis

if id $name &> /dev/null;then
echo "$name exists"
else
echo "$name does not exist"
echo $name | passwd --stdin $name
useradd $name 
echo "Add $name finished"
fi

练习

1. 给一个用户，UID为0，显示为管理员，
   否则，显示为普通用户

nano par.sh

#!/bin/bash
name=yli
userid=`id -u $name`
if [ $userid -eq 0 ]; then #或者 if [ `id -u $name` -eq 0 ] 则不要上一个变量
echo "$name is the Admin"
else
echo "$name is a user"
fi

$ chmod +x par.sh
$ ./pra.sh 
yli is a user

2. 显示用户shell为bash的用户

$ nano bash.sh

#!/bin/bash
#
grep '\bbash$' /etc/passwd &> /dev/null
stat=$?
if [ $stat -eq 0 ]; then
 users=`grep '\bbash$' /etc/passwd | wc -l`
 echo "$users users"
 names=`grep '\bbash$' /etc/passwd | cut -d: -f1`
 echo -e  "their names are \n$names"
else
 echo "no such user."
fi

$ chmod +x bash.sh
$ ./bash.sh
20 users
their names are 
root
ubuntu
jmzeng
spguo
fzhao
zgxu
myshen
syqu
yxwei
htwang
xlwan
tercent
jksong
dzhang
lmsong
yxiao
gyli
xyli
hocchan
yinqi

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