Using sed to replace one line (that might change) with another

Question

I want to run a script that changes a line in the HTML code, indicating when the page was last updated. So for instance, I have the line

<d>This page was last updated on 29.04.2013 at 00:34 UTC</d>

and I am updating it now, so I want to replace that line with

<d>This page was last updated on 15.05.2013 at 15:50 UTC</d>

This is the only line in my source code that has the <d> tag, so hopefully that helps. I already have some code that generates the new string with the current date and time, but I can't figure out a way to replace the old one (which changes, so I don't know exactly what it is).

I've tried putting in a comment  in the previous line, deleting the whole line that has <d> (with grep), and then putting in a new line after the comment that is the new string, but that fails. For example, if I want to just insert the string text after the comment, and use

sed -i 's//text/' file.html

I get invalid command code j. I think it might be because there are some special characters like <,!, and > in the strings, but if I want to put in the date string above, I will have even more, like : and /. Thanks for any ideas on how to fix this.

Believe it or not, I think the problem is that you are using `csh` or some other shell that is trying to do a history expansion on the `!` inside single quotes. Try using a different shell. — William Pursell, May 15 '13 at 15:00

Markku K. · Answer 1 · 2013-05-15T15:54:37.033

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You don't need your  hack. You can use regular expressions and another delimiter besides "/" in your sed command:

sed -i.bak 's@<d>This page was last updated on.*</d>@<d>This page was last updated on 12.05.2013 at 00:38 UTC</d>@' whatever.html

Or, if you have your update in a variable called $replacement:

sed -i.bak "s@<d>This page was last updated on.*</d>@$replacement@" whatever.html

edited May 15 '13 at 15:54

answered May 15 '13 at 15:02

Markku K.

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Nope, in both cases, using `bash` or `sh`, I get the same error. I should mention I'm running Mac OS 10.7.5 – Jānis Lazovskis May 15 '13 at 15:11
Hmm ... works in bash, csh, and zsh on my Linux box ... sorry then, I don't know! – Markku K. May 15 '13 at 15:20
OK, see [this](https://github.com/bergie/create/pull/119) ... you need a "backup" extension on your -i ... -i.bak or whatever. – Markku K. May 15 '13 at 15:22
Great, now it works! But there should be no space between `-i` and `.bak`, otherwise it fails. – Jānis Lazovskis May 15 '13 at 15:32
That's funny ... I originally had it without the space, but I saw [this answer](http://stackoverflow.com/questions/4247068/sed-command-failing-on-mac-but-works-on-linux) which had a space. – Markku K. May 15 '13 at 15:57

chthonicdaemon · Accepted Answer · 2013-05-15T15:12:35.570

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This will change the text only on lines that contain <d>:

sed -i.bak "/<d>/s/on .* at [^<]*/on newdate at newtime/" file.html

I've tested this with the BSD sed that ships with MacOS X 10.8.3

edited May 15 '13 at 15:12

answered May 15 '13 at 15:03

chthonicdaemon

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Perfect. Creates a `.bak` file too, but that doesn't really matter. – Jānis Lazovskis May 15 '13 at 15:16
I've been bitten a couple of times by not having that bak file, so I put it in without thinking. You can, of course, remove it. – chthonicdaemon May 15 '13 at 15:18

score 0 · Answer 3 · answered May 15 '13 at 14:57

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When using the command line, try escaping special characters like this:
! ===> \!

answered May 15 '13 at 14:57

yoones

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No dice. Same error, using it only for `!`, or for `!`,`<`, and `>`. – Jānis Lazovskis May 15 '13 at 15:00

Using sed to replace one line (that might change) with another

3 Answers3