NAME

true — return true value

SYNOPSIS

true

DESCRIPTION

The true utility shall return with exit code zero.

OPTIONS

None.

OPERANDS

None.

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

None.

ASYNCHRONOUS EVENTS

Default.

STDOUT

Not used.

STDERR

Not used.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

Zero.

CONSEQUENCES OF ERRORS

None.

APPLICATION USAGE

This utility is typically used in shell scripts, as shown in the EXAMPLES section.

Although the special built-in utility : (colon) is similar to true, there are some notable differences, including:

• Whereas colon is required to accept, and do nothing with, any number of arguments, true is only required to accept, and discard, a first argument of "--". Passing any other argument(s) to true may cause its behavior to differ from that described in this standard.

• A non-interactive shell exits when a redirection error occurs with colon (unless executed via command), whereas with true it does not.

• Variable assignments preceding the command name persist after executing colon (unless executed via command), but not after executing true.

• In shell implementations where true is not provided as a built-in, using colon avoids the overheads associated with executing an external utility.

EXAMPLES

This command is executed forever:

while true
do
    command
done

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

2.9 Shell Commands , colon , command , false

CHANGE HISTORY

First released in Issue 2.

Issue 6

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/39 is applied, replacing the terms "None" and "Default" from the STDERR and EXIT STATUS sections, respectively, with terms as defined in 1.4 Utility Description Defaults .

Issue 8

Austin Group Defect 1640 is applied, clarifying the differences between true and : (colon).