Date: Mon, 18 Oct 2004 13:34:37 +0000 From: Richard Bradley <rtb27@cam.ac.uk> To: freebsd-questions@freebsd.org Subject: How to run a stream based command in place on a file Message-ID: <200410181334.37665.rtb27@cam.ac.uk>
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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? 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
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