if

Shell conditional statement

TLDR

Basic if statement

$ if [[ condition ]]; then command; fi

If-else

$ if [[ -f file ]]; then echo "exists"; else echo "missing"; fi

If-elif-else

$ if [[ $x -eq 1 ]]; then cmd1; elif [[ $x -eq 2 ]]; then cmd2; else cmd3; fi

Test file exists

$ if [[ -e file ]]; then echo "found"; fi

Test string equality

$ if [[ "$a" == "$b" ]]; then echo "equal"; fi

Test command exit status

$ if grep -q "pattern" file; then echo "found"; fi

Numeric comparison

$ if [[ $count -gt 10 ]]; then echo "more than 10"; fi

SYNOPSIS

if test-commands; then commands; [elif test-commands; then commands;] [else commands;] fi

if is a shell builtin conditional statement. It executes the test-commands list and, if the exit status is zero (success), runs the corresponding then clause. If non-zero, each elif clause is tested in turn. If no condition succeeds and an else clause is present, its commands are executed.Although if is most commonly used with test or [[ ]] expressions, any command can serve as the condition since the decision is based on exit status. For example, if grep -q pattern file branches on whether grep found a match.

PARAMETERS

test-commands

A list of commands whose exit status determines the branch taken. An exit status of 0 (success) means the condition is true.

then

Introduces commands to execute when the preceding condition is true.

elif

Else-if clause; tests an additional condition if prior conditions were false.

else

Commands to execute if all preceding conditions were false.

End of the if block.

CAVEATS

Shell builtin. Spaces inside [ ] and [[ ]] are required (e.g., [ "$a" = "$b" ], not ["$a"="$b"]). The POSIX-compatible test syntax is [ ], while [[ ]] is a bash/zsh extension with additional features like pattern matching and regex.

HISTORY

if is a standard Unix shell construct, present in all POSIX-compliant shells since the original Bourne shell.

if