Date: Wed, 27 Oct 2010 22:04:52 -0400 (EDT) From: vogelke+unix@pobox.com (Karl Vogel) To: freebsd-questions@freebsd.org Subject: Re: [OT] writing filters in sh Message-ID: <20101028020452.A282DBF80@kev.msw.wpafb.af.mil> In-Reply-To: <20101027212841.GA67716@guilt.hydra> (message from Chad Perrin on Wed, 27 Oct 2010 15:28:41 -0600)
next in thread | previous in thread | raw e-mail | index | archive | help
>> On Wed, 27 Oct 2010 15:28:41 -0600,
>> Chad Perrin <perrin@apotheon.com> said:
C> In Perl, you can use a single construct to [read files or pipes], and it
C> can also take multiple filenames as arguments and effectively
C> concatenate their contents:
C> while (<>) { print $_; }
C> Please let me know if there's some way to use a simple idiom like the
C> Perl example to get the same results in sh.
AFAIK, you can easily do *one* input and output file, but not multiple
input files like the Perl "diamond" operator unless you want to play
games with the argument list. This works with sh, ksh, and bash on
FreeBSD and Solaris:
#!/bin/sh
# filter: handle input/output files or stdin/stdout.
# usage: filter [input] [output]
# ie: filter read stdin, write stdout
# filter in read file "in", write stdout
# filter in out read file "in", write file "out"
# filter - out read stdin, write file "out"
PATH=/usr/local/bin:/bin:/usr/bin; export PATH
case "$1" in
"") ;;
"-") shift ;;
*) exec <"$1"; shift ;;
esac
case "$1" in
"") ;;
*) exec >"$1" ;;
esac
wc # or whatever
exit 0
--
Karl Vogel I don't speak for the USAF or my company
We seem not to have learned a basic lesson of history: Capitalism harnesses
self-interest; socialism exhausts itself trying to kill it. --Linda Bowles
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20101028020452.A282DBF80>