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I am trying to replace _ with : in a file on a Unix system using sed:

sed "s/'_''/:/g"

However, it doesn't work. I cannot find a solution in similar sed related posts.

AdminBee
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user485085
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  • Related: [What characters do I need to escape when using sed in a sh script?](https://unix.stackexchange.com/q/32907/170373) and maybe also [What characters need to be escaped in files without quotes?](https://unix.stackexchange.com/q/347332/170373) – ilkkachu Aug 01 '21 at 20:54

1 Answers1

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You have an extra single quote, and, in fact, don't need the quotes at all. The underscore and the colon are not significant to the shell. You are asking sed to match '_'' (all four characters) and replace them with a colon.

$ echo "_This is a test_" | sed s/_/:/g  
:This is a test:

Not that quotes aren't a good idea...

AdminBee
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Marc Wilson
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    Also, more efficient: `sed 'y/_/:/'`, or even `tr '_' ':'` (or just `tr _ :` if you want to save on typing). – Kusalananda Aug 01 '21 at 20:10
  • The double quotes are not necessary, the stream presented to `sed` in the example is the same in any case. I would agree that if there were shell metacharacters in the stream, like a glob, you'd have a problem, but then add a comment explaining it. – Marc Wilson Aug 01 '21 at 22:33