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
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