colon - Man Page

null utility

Prolog

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

Synopsis

: [argument...]

Description

This utility shall only expand command arguments. It is used when a command is needed, as in the then condition of an if command, but nothing is to be done by the command.

Options

None.

Operands

See the Description.

Stdin

Not used.

Input Files

None.

Environment Variables

None.

Asynchronous Events

Default.

Stdout

Not used.

Stderr

The standard error shall be used only for diagnostic messages.

Output Files

None.

Extended Description

None.

Exit Status

Zero.

Consequences of Errors

Default.

The following sections are informative.

Application Usage

None.

Examples

: ${X=abc}
if     false
then   :
else   echo $X
fi
abc

As with any of the special built-ins, the null utility can also have variable assignments and redirections associated with it, such as:

x=y : > z

which sets variable x to the value y (so that it persists after the null utility completes) and creates or truncates file z.

Rationale

None.

Future Directions

None.

See Also

Section 2.14, Special Built-In Utilities

Info

2017 IEEE/The Open Group POSIX Programmer's Manual