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dup(F)


dup -- duplicate an open file descriptor

Description

Opening a dup character special file is equivalent to a dup(S) of the file descriptor with the same number as the minor device.

The character special files /dev/stdin, /dev/stdout, and /dev/stderr correspond to the standard input, output, and error respectively.

Examples

The following commands have the same effect:

cat /dev/stdin skywards < apult
cat - skywards < apult
cat apult skywards

Another example is writing to the standard error from an awk script; the following awk actions are equivalent:

{ ... print "$1 is an illegal value" | "cat >&2"; ... }
{ ... print "$1 is an illegal value" > "/dev/stderr"; ... }

The following commands use a temporary file to compare the contents listings of two tar(C) archives:

tar tvf archive1 > /tmp/$$
tar tvf archive2 | diff - /tmp/$$
rm -f /tmp/$$

ksh process redirection can be used instead:

diff <(tar tvf archive1) <(tar tvf archive2)

Limitations

Not all /dev/fd/* files may be present on your system.

Files


/dev/stdin
corresponds to the standard input

/dev/stdout
corresponds to the standard output

/dev/stderr
corresponds to the standard error

/dev/fd/0 - /dev/fd/99
correspond to the file descriptors 0 to 99

See also

awk(C), dup(S), ksh(C), sh(C), tar(C)
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003