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(gawk.info)Special Caveats

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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 (Note: Command-Line Options.).

   * 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.  Note: 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 only interpret these names
internally if the system did not actually have a a `/dev/fd' directory
or any of the other above listed special files.  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.