Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!spool.mu.edu!uunet!mcsun!ukc!pyrltd!root44!gwc
From: gwc@root.co.uk (Geoff Clare)
Newsgroups: comp.unix.shell
Subject: Re: cat, pipes, and filters
Message-ID: <2730@root44.co.uk>
Date: 4 Jun 91 13:03:32 GMT
Article-I.D.: root44.2730
References: <1991May31.165446.1530@progress.com> <10918@chorus.fr>
Organization: UniSoft Ltd., London, England
Lines: 25

In <10918@chorus.fr> bp@chorus.fr (Bruno Pillard) writes:

>What about:

>  ( /bin/rm $FILE ; sed  s/"$ENTRY"/"$NEWENTRY"/ > $FILE ) < $FILE

>I understand that this may look harmful at first glance because of the
>/bin/rm of your precious file but it  works perfectly for  me under sh
>and (t)csh.

>Is there any problem using that construction ?

Yes!  If any errors occur you lose your data.

Slightly better would be:

  ( /bin/rm $FILE && sed  s/"$ENTRY"/"$NEWENTRY"/ > $FILE ) < $FILE

which would not truncate the file if the "rm" fails, but this still
loses your data if the disk is full.  It's much safer to:

  sed  s/"$ENTRY"/"$NEWENTRY"/ < $FILE > $TMPFILE && mv $TMPFILE $FILE
-- 
Geoff Clare <gwc@root.co.uk>  (Dumb American mailers: ...!uunet!root.co.uk!gwc)
UniSoft Limited, London, England.   Tel: +44 71 729 3773   Fax: +44 71 729 3273