# expr
# Evaluate expressions and manipulate strings.
# More information: <https://www.gnu.org/software/coreutils/expr>.
# Get the length of a specific string:
expr length "string"
# Get the substring of a string with a specific length:
expr substr "string" from length
# Match a specific substring against an anchored pattern:
expr match "string" 'pattern'
# Get the first char position from a specific set in a string:
expr index "string" "chars"
# Calculate a specific mathematic expression:
expr expression1 +|-|*|/|% expression2
# Get the first expression if its value is non-zero and not null otherwise get the second one:
expr expression1 \| expression2
# Get the first expression if both expressions are non-zero and not null otherwise get zero:
expr expression1 \& expression2
$
cheat.sh
tldr