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.

NAME¶

colon - null utility

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¶

Special Built-In Utilities

COPYRIGHT¶

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .