Date: Mon, 18 Oct 2004 13:48:22 +0100 (BST) From: Vince Hoffman <jhary@unsane.co.uk> To: Richard Bradley <rtb27@cam.ac.uk> Cc: freebsd-questions@freebsd.org Subject: Re: How to run a stream based command in place on a file Message-ID: <20041018134625.F63651@unsane.co.uk> In-Reply-To: <200410181334.37665.rtb27@cam.ac.uk> References: <200410181334.37665.rtb27@cam.ac.uk>
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On Mon, 18 Oct 2004, Richard Bradley wrote: > Hi, > > I want to run stream based commands like `sed` and `tr` on the contents of a > file, and save the results to the same file. > > Obviously I can do this with a temporary file: > > $sed s/dog/cat/ myanimals.txt > tmp.txt > $mv tmp.txt myanimals.txt > > But is there any way I can do this with a single command? Not sure about tr but sed does give the -i option to edit in place. I'm not sure about a more general solution though. > > My first guess would be a "buffer" command that reads a file into memory (or > into a temp file) then pipes it to stdout, e.g. > > $cat myanimals.txt | buffer | sed s/dog/cat/ > myanimals.txt > > But there isn't one which, in my experience of BSD, means it either wouldn't > work or there is a better way to do it :-) > > Having read through the Bash manual and run some experiments, it seems that > the ">" operator truncates an output file to zero length before any commands > are run. > > So my missing command becomes: > > $cat myanimals.txt | sed s/dog/cat | bufferedwrite myanimals.txt > > I can't find anything like this anywhere -- any ideas what the "proper" way to > do this is? > > Thanks in advance, > > > Rich > > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to "freebsd-questions-unsubscribe@freebsd.org" >
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