shell脚本编程之基础篇（二）
# [ tom == Tom ]# echo $?
1
# [ tom == tom ]
# echo $?
0
# 变量替换要尽量用双引号，如果不用的话，如果变量不存在为空，会报错
# [ tom == $name ]
-bash: [: tom: 期待一元表达式
# [ tom == "$name" ]
# echo $?
1
# [[ tom == $name ]]
# echo $?
1
# name=xiu
# [ tom == $name ]
# echo $?
1
# [ tom == "$name" ]
# echo $?
1
# 要尽量使用 [[ ]]
# [ 'a' > 'b' ]
# echo $?
0
# [ 'a' < 'b' ]
# echo $?
0
# [[ 'a' > 'b' ]]
# echo $?
1
# [[ 'a' < 'b' ]]
# echo $?
0
# 在 [] 中变量替换一定要加双引号，但是在 [[ ]] 中可以不加
# [ -z $a ] && echo yes || echo no
yes
# [ -n $a ] && echo yes || echo no
yes
# [ -n "$a" ] && echo yes || echo no
no
# [ -z "$a" ] && echo yes || echo no
yes
# [[ -n $a ]] && echo yes || echo no
no
# [[ -z $a ]] && echo yes || echo no
yes
#============================================================================
# name=haha
# echo $name
haha
# [[ "$name" =~ ha ]]
# echo $?
0
# [[ "$name" =~ h ]]
# echo $?
0
# [[ "$name" =~ hx ]]
# echo $?
1
# [[ "$name" =~ xx ]]
# echo $?
1
页:
[1]