Deletion, substitution and substitution of shell variable contents

Deletion of shell variables:

[Email protected]:~$ Path=${path} # #设置path和PATH相同内容 [email protected]:~$ echo $path/usr/local/sbin:/usr/local/bin:/ Usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games[email protected]:~$ echo ${path#/*sbin:} # #加上 ' # ' symbol delete Match '/* Sbin: ' Minimum combination/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games[email protected]:~$ echo ${ Path##/*sbin:} # #加上 ' # # ' delete match '/*sbin: ' Maximum combination/bin:/usr/games:/usr/local/games

Variable Setting method	Description
${variable # keyword}	Delete the shortest combination if the variable content starts with the data in the keyword
${variable # #关键字}	Delete the longest combination if the variable content starts with the "keyword" data
${Variable% keyword}	Delete the shortest combination if the variable content starts at the end of the data that matches the keyword
${Variable% keyword}	Delete the longest combination if the variable content starts at the end of the data that matches the keyword
${variable/old string/new string}	Replace the first old string with a new string if the contents of the variable conform to the old string
${variable//old string//new String}	Replace the first old string with a new string if the contents of the variable conform to the old string

Substitution of shell variables:

[Email protected]:~$ Path=${path} # #设置path和PATH相同内容 [email protected]:~$ echo $path/usr/local/sbin:/usr/local/bin:/ Usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games[email protected]:~$ Echo ${path/sbin/newsbin} # # Replace the first sbin with a newsbin/usr/local/newsbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games[ Email protected]:~$ Echo ${path//sbin//newsbin} # #将所有的sbin替换成newsbin/usr/local//newsbin:/usr/local/bin:/usr// Newsbin:/usr/bin://newsbin:/bin:/usr/games:/usr/local/games

Substitution of shell variables:

How variables are set	Str not set	STR is empty	STR contains content
VAR=${STR-EXPR}	var=expr	Var=	Var= $str
VAR=${STR:-EXPR}	var=expr	var=expr	Var= $str
VAR=${STR+EXPR}	Var=	var=expr	var=expr
VAR=${STR:+EXPR}	Var=	Var=	var=expr
VAR=${STR=EXPR}	str=expr var=expr	Str= not change var=	str= unchanged var= $str
VAR=${STR:=EXPR}	str=expr var=expr	str=expr var=expr	str= unchanged var= $str
VAR=${STR?EXPR}	Expr output to stderr	Var=	Var=str
VAR=${STR:?EXPR}	Expr output to stderr	Expr output to stderr	Var=str

Deletion, substitution and substitution of shell variable contents