expr

Evaluate expressions and manipulate strings.

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• Get string length:

expr length {string}

• Evaluate logical or math expression with an operator ('+', '-', '*', '&', '|', etc.). Special symbols should be escaped:

expr {first_argument} {operator} {second_argument}

• Get position of the first character in 'string' that matches 'substring':

echo $(expr index {string} {substring})

• Extract part of the string:

echo $(expr substr {string} {position_to_start} {number_of_characters}

• Extract part of the string which matches a regular expression:

echo $(expr {string} : '\({regular_expression}\)')

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