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using sed to replace the contents of a file is not working in bash script

Answer 1

+4 A:

Try this:

sed -i -e 's/<em\:update.*//g' install.rdf

When you redirect output to a file in truncate mode, the file is truncated first, before it's read. Thus, the result is an empty file. Using sed -i avoids this.

Portable (and hopefully not too insecure) solution:

(set -C &&
 sed -e 's/<em\:update.*//g' install.rdf > install.rdf.$$ &&
 mv install.rdf.$$ install.rdf)

:-)

Chris Jester-Young 2010-10-07 23:59:53

However, `-i` is a GNU extension.

Matthew Flaschen 2010-10-08 00:03:34

@Matthew: Thanks! Fixed up the answer with something a little more general (albeit insecure if the directory is writable by malicious parties).

Chris Jester-Young 2010-10-08 00:05:31

The shell variable $$ is classically used for non-hostile environments avoiding problems with shared names: `sed ... install.rdf > install.rdf.$$; mv install.rdf.$$ install.rdf`.

Jonathan Leffler 2010-10-08 00:21:32

@Jonathan: I've revised my solution with your suggestion, as well using `set -C` to mitigate symlink attacks or anything. It can fail if the filename is already taken, but at least people can't trick you into clobbering files you don't intend to. ;-)

Chris Jester-Young 2010-10-08 02:00:54

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using sed to replace the contents of a file is not working in bash script

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