shell 字符相等判断问题。

linfengfeiye

#!/bin/sh
cpasswd=sc
b=x
if [ "$cpasswd"="$b" ]
then
  echo "equal"
fi

为什么我运行后会打印equal呢，明明不等嘛。

昭襄王

if [ $cpasswd == $b ]; then echo "equal"; fi

linfengfeiye

[root@t153 ~]# if [ $cpasswd == $b ]; then echo "equal"; fi
equal
[root@t153 ~]#

昭襄王

b=sc
if [ $cpasswd == $b ]; then echo "equal"; fi
equal

b=x
if [ $cpasswd == $b ]; then echo "equal"; fi

linfengfeiye

root@h1:~# cat test2
#!/bin/sh
cpasswd=sc
b=sc
if [ $cpasswd == $b ]; then echo "equal"; fi
b=x
if [ $cpasswd == $b ]; then echo "equal"; fi
root@h1:~# ./test2
[: 4: ==: unexpected operator
[: 6: ==: unexpected operator
root@h1:~# bash -version
GNU bash, version 3.2.39(1)-release (i486-pc-linux-gnu)
Copyright (C) 2007 Free Software Foundation, Inc.
root@h1:~#

linfengfeiye

root@h1:~# cat test2
#!/bin/sh
cpasswd=sc
b=sc
if [ $cpasswd==$b ]; then echo "equal"; fi
b=x
if [ $cpasswd==$b ]; then echo "equal"; fi
root@h1:~# ./test2
equal
equal
root@h1:~#

linfengfeiye

root@h1:~# cat test2
#!/bin/sh
cpasswd=sc
b=sc
if [ "$cpasswd"=="$b" ]; then echo "equal"; fi
b=x
if [ "$cpasswd"=="$b" ]; then echo "equal"; fi
root@h1:~# ./test2
equal
equal
root@h1:~#

linfengfeiye

root@h1:~# cat test2
#!/bin/sh
cpasswd=sc
b=sc
if [ "$cpasswd"=="$b" ]; then echo "equal"; fi
b=x
if [ "$cpasswd"=="$b" ]; then echo "equal"; fi
root@h1:~# ./test2
equal
equal
root@h1:~# cpasswd=sc
root@h1:~# b=sc
root@h1:~# if [ $cpasswd == $b ]; then echo "equal"; fi
equal
root@h1:~# b=x
root@h1:~# if [ $cpasswd == $b ]; then echo "equal"; fi
root@h1:~#

linfengfeiye

找到原因了。

root@h1:~# ls -l /bin/sh
lrwxrwxrwx 1 root root 4 Jun 20  2008 /bin/sh -> dash

L_kernel

1. # cpasswd=sc
   
2. # b=x
   
3. # [ "$cpasswd" == "$b" ] && echo "equal"
   
4. #

复制代码