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.
colon — null utility
This utility shall only expand command argument
s. It is used when a
command is needed, as in the then
condition of an if
but nothing is to be done by the command.
See the DESCRIPTION.
The standard error shall be used only for diagnostic messages.
The following sections are informative.
else echo $X
As with any of the special built-ins, the null utility can also have variable
assignments and redirections associated with it, such as:
which sets variable x
to the value y
(so that it persists after
the null utility completes) and creates or truncates file z
, Special Built-In Utilities
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
7, Copyright (C) 2013 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013
Technical Corrigendum 1 applied.) 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.unix.org/online.html .
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