tldr/pages/common/expr.md

expr

Evaluate expressions and manipulate strings.

• 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}} : '\({{regular_expression}}\)')