[root@localhost ~]# echo ${MAIL}
/var/spool/mail/root
[root@localhost ~]# echo ${MAIL##/*/} #贪婪前匹配删除
root
[root@localhost ~]# echo ${MAIL#/*/} #前匹配删除
spool/mail/root
[root@localhost ~]# echo ${MAIL%/*} #后匹配删除
/var/spool/mail
[root@localhost ~]# echo ${MAIL%%/*} #贪婪后匹配删除
[root@localhost ~]# echo ${MAIL//oo/aa} #全局替换
/var/spaal/mail/raat
[root@localhost ~]# echo ${MAIL/oo/aa} #仅替换第一个
/var/spaal/mail/root
[root@localhost ~]# unset a;var=${a-b};echo $a,$var # var = (a == null) ? a : b
,b
[root@localhost ~]# a='foo';var=${a-b};echo $a,$var
foo,foo
[root@localhost ~]# unset a;var=${a=b};echo $a,$var # var = a= (a == null)? a : b
b,b
[root@localhost ~]# a='foo';var=${a=b};echo $a,$var
foo,foo
| 变量设置方式 | str没有设置 | str为空字符 | str已设置为非空字符 |
| var=${str-expr} | var=expr | var= | var=$str |
| var=${str:-expr} | var=expr | var=expr | var=$str |
| var=${str+expr} | var=expr | var=expr | var=expr |
| var=${str:+expr} | var=expr | var= | var=expr |
| var=${str=expr} |
var=expr |
str不变 var= |
str不变 var=$str |
| var=${str:=expr} |
var=expr |
var=expr str=expr |
str不变 var=$str |
| var=${str?expr} | expr输出至stderr | var= | var=$str |
| var=${str:?expr} | expr输出至stderr | expr输出至stderr | var=$str |