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Re: Cleaner way of looping through a file and stripping only certain lines?

by hiseldl (Priest)
on Dec 08, 2006 at 21:31 UTC ( #588708=note: print w/replies, xml ) Need Help??

in reply to Cleaner way of looping through a file and stripping only certain lines?

I did not see the requirement that you wanted a script, so, here's how I would do it...

You can use the '-i' switch to edit the file in-place. See perlrun for reference.

If you do not want to create a backup file...

$ perl -ni -e '$match=/::mail(\d+)/;print if!$match||$1>7' data

If you do want to create a backup file with extension '.bak'...

perl -ni.bak -e '$match=/::mail(\d+)/;print if!$match||$1>7' data

This assumes that the file containing the data is named 'data'.

Here's the nuts-and-bolts explanation, skip it if you already know how it works.

Basically, this will check every line to see if it matches the regex, in your case you wanted to match something like /::mail(\d+)/ to capture the digits (please put whatever regexp you need in there, this is untested and for example purposes only). The match operator is used for two purposes, (1) letting us know if it matched, and (2) capturing the digits of interest if it does match. Here, I store the boolean value in $match for later usage. The second statement is the conditional print, which will print the current line if it did not match or if the value of the captured digits is greater than 7.

Please change it according to your needs.


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LanX is pretty brown in summer
[Your Mother]: Though a bad match for the OP in question here. :P
[Corion]: Your Mother: Yeah
[Your Mother]: Americans are still pumping out video games where you get to slaughter as many Germans as you have the GPU for... It has always struck me as odd that this particular case seems fine to people. :\
[LanX]: yep heard the same origin story
[Your Mother]: I like it. I tottered on going into hucksterism because I feel like the world deserves it.
[LanX]: he ... we have a movement here called Anti-Germans based on this
[Corion]: Your Mother: I think that's because (in the west) the Nazi-Germans are recognized as universally evil. Of course, you could do some number games to calculate other measures of evil than "historic losers of second world war" to come up with other evils:)
[Corion]: I've heard "Troll" described as the new Punk, and in a way, it can be as destructive as living the Punk lifestyle, and you don't have to sit out in the cold...
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