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.

INSTALL

sudo apk add execline

brew install execline

nix profile install nixpkgs#execline

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