Linux Shell parameter substitution

Linux Shell parameter substitution

2013-06-03 10:01 by Xuan Blade, 1816 Read, 0 reviews, Favorites, compilation

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, the curly braces are optional, i.e.A and

{A} represents the same parameter.

${} There are several expressions with colons: ${parameter:-word}

If parameter is null or not set, the entire parameter substitution expression value is word

${parameter:=word}

If parameter is null or not set, the entire parameter substitution expression value is word, and the parameter parameter value is set to Word

${parameter:?word}

If parameter is null or not set, an error message is printed. Otherwise, the entire parameter substitution expression value is $parameter

${parameter:+word}

If parameter is not NULL or not set, the entire parameter substitution expression value is word

${parameter:offset}${parameter:offset:length}

A substring of the value of the parameter.

Here are some examples to understand:

${} band! There are several expressions: ${!prefix*}${[email protected]}

Prints the name of the parameter with the prefix prefix

${!name[@]}${!name[*]}

This is for the name array, which prints out what subscript the name array has

Here are some examples to understand:

${} Several expressions with regular matches: ${parameter#word}${parameter# #word}

Scan Word from the beginning to filter out characters that match the word's regular expression

#为最短匹配, # #为最长匹配

${parameter%word}${parameter%%word}

Scan Word from the end to filter out characters that match the word regular expression

% is the shortest match and the percent is the longest match

Here are some examples to understand:

${parameter/pattern/string}${parameter//pattern/string}

Replace the pattern string of the parameter corresponding value with a string string

/means replace only once

means replace All

Here are some examples to understand:

Linux Shell parameter substitution