Node:Special Caveats, Previous:Special Network, Up:Special Files

Special File Name Caveats

Here is a list of things to bear in mind when using the special file names that gawk provides:

• Recognition of these special file names is disabled if gawk is in compatibility mode (see Command-Line Options).
• The As mentioned earlier, the special files that provide process-related information are now considered obsolete and will disappear entirely in the next release of gawk. gawk prints a warning message every time you use one of these files. To obtain process-related information, use the PROCINFO array. See Built-in Variables.
• Starting with version 3.1, gawk always interprets these special file names.¹ For example, using /dev/fd/4 for output actually writes on file descriptor 4, and not on a new file descriptor that is dup'ed from file descriptor 4. Most of the time this does not matter; however, it is important to not close any of the files related to file descriptors 0, 1, and 2. Doing so results in unpredictable behavior.

Footnotes

1. Older versions of gawk would interpret these names internally only if the system did not actually have a /dev/fd directory or any of the other special files listed earlier. Usually this didn't make a difference, but sometimes it did; thus, it was decided to make gawk's behavior consistent on all systems and to have it always interpret the special file names itself.