if

Basic if statement

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

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

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

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

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

if condition; then commands; [elif condition; then commands;] [else commands;] fi

if is a shell conditional statement. It executes commands based on the exit status of test conditions.
The construct supports multiple conditions with elif and a fallback else clause. It's fundamental to shell scripting.

CONDITION

Test expression.

Commands if true.

Else-if clause.

Commands if false.

End if block.

Shell builtin. Spaces in conditions matter. Use [[ ]] in bash.

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

test(1), case(1), bash(1)