The let builtin

let <EXPRESSION>

The let builtin command evaluates the arithmetic expression <EXPRESSION> and returns the exit codes

• 0 (TRUE) when <EXPRESSION> evaluated to not 0 (arithmetic "true")
• 1 (FALSE) when <EXPRESSION> evaluated to 0 (arithmetic "false")

The form (note the quoting!)

let "<EXPRESSION>"

is identical to the arithmetic evaluation compound command

(( <EXPRESSION> ))

This way should be preferred.

The let command is not specified by POSIX®. The standard equivalent is:

[ "$(( <EXPRESSION> ))" -ne 0 ]

The quotes around the arithmetic expansion are only necessary with bash and AT&T versions of ksh, other standard shells such as ash, pdksh or zsh derivatives don't have that bug/misfeature.

• Internal: arithmetic expansion
• Internal: arithmetic expressions
• Internal: arithmetic evaluation compound command