$ curl cheat.sh/
# expr
# Evaluate expressions and manipulate strings.
# More information: <https://www.gnu.org/software/coreutils/expr>.

# 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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