Re: tlug: sed ?

["Stephen J. Turnbull" <turnbull@example.com>]

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tlug note from "Stephen J. Turnbull" <turnbull@example.com>
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>>>>> "Jim" == Jim Schweizer <schweiz@example.com> writes:

    Jim> After the great help a couple of weeks ago on using sed to
    Jim> strip headers from email I decided to try to learn a little
    Jim> more about it. So, I ordered the O'Reilly 'sed & awk' book
    Jim> and got to work.

    Jim> The problem is, sometime things don't work as advertised. For
    Jim> example in chapter 3 you're supposed to make a program for
    Jim> making single replacements called 'gres' which looks like:

    Jim> jim:~/bin$ cat gres

Hmmmm...  where's your magic shell interpreter thingie?  Try inserting 

#!/bin/sh

because bash and sh are not the same, quite, but calling bash as sh
makes it much more compatible.  This in fact doesn't work here :-)

    Jim> if [ $# -lt "3" ]
    Jim> then
    Jim>         echo Usage: gres pattern replacement file
    Jim>         exit 1
    Jim> fi
    Jim> pattern=$1
    Jim> replacement=$2
    Jim> if [ -f $3 ]
    Jim> then
    Jim>         file=$3
    Jim> else
    Jim>         echo $3 is not a file
    Jim>         exit 1
    Jim> fi
    Jim> A="'echo | tr '\012' '\001' '"
    Jim> 
    Jim> sed -e "s$A$pattern$A$replacement$A" $file

I assume that this is a hack which allows you to use a nonprintable,
and thus highly unlikely to appear in the pattern or replacement,
separator in the `s' command.  Such hacks tend to be very unportable
across shells.

If you substitute backquotes for the "' and '" pairs, it works.  I
couldn't find a way to get around the shell variable A, though.

    Jim> When I try to use it though I get the error:

    Jim> sed: Unknown option to 's'

Me, too.

    Jim> So I tried in on both my Slackware setup and SparkLinux with
    Jim> the same result.

    Jim> The book was written and tested on a SparcStation 1 running
    Jim> SunOS 4.0. Is the Linux sed version different? I'm using GNU
    Jim> sed version 2.05; should I upgrade?

It's not sed that's different, it's the shell.  Our Suns run csh by
preference, maybe this is a csh-ism.

FIRST, blame the shell.  Then look for problems with other programs ;-)

Steve


-- 
                            Stephen J. Turnbull
Institute of Policy and Planning Sciences                    Yaseppochi-Gumi
University of Tsukuba                      http://turnbull.sk.tsukuba.ac.jp/
Tel: +81 (298) 53-5091;  Fax: 55-3849              turnbull@example.com
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