I’m editing a big HTML file, with a bunch of CSS classes that. I want to convert everything that says:
**\
**
where XXX is a number from 1-652, into
**\
**
Except for classes 115, 121, 122, 130, 134, 137, 140, 146, 147, 148, and 149, which I want to convert to
**\
**
I figured out how to match up those classes with the following regex-using perl program:
```auto
open(INPUT,"<$ARGV[0]") or die;
@input_array=;
close(INPUT);
$input_scalar=join("",@input_array);
$input_scalar =~ s/(
)(.*?)(<\/p>)/
\3<\/p>/g;
print($input_scalar);
```
This takes an input file and prints it to standard out; I usually redirect it to a file after I determine that it works.
That handles all those “exceptional” classes. But how can I invert that to come up with my other search and replace? There are way too many numbers to put them all in like I did with that one…
Thanks for any help.
---
Perl supports a zero-width negative look-ahead assertion (which also happens to be my favorite instance of regex jargon.)
So you can do this:
```auto
s/(
/
### Author:  [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)
#### Post date: [April 9, 2009, 12:47am UTC](https://boards.straightdope.com/t/regular-expression-matching-everything-but/492463/3 "2009-04-09T00:47:35Z")
It’s not elegant, but you can use one regex to make sure that you have a tag of the form \
, and then use another regex to decide whether that three-digit sequence is in that list. If so, replace it with Blockquote; if not, replace it with Normal.
---
Thanks, **friedo**! I had found the zero-width negative look-ahead operator before, but I left off the trailing **\d{1,3}** (just **\d{3}** won’t do it because, as I forgot to mention, the styles go from Style1 to Style652, rather than Style001) and it was only matching the **Style** text and was leaving the numbers unchanged, so I thought I was misunderstanding “zero-width negative look-ahead.” But of course, I just had it wrong. Thanks!
**ultrafilter** , I thought about doing something like that, but it’s been so long since i used perl that I’ve completely forgotten it, so I couldn’t tell how to put the output of one regex into the next and still output the whole file the way my current search-and-replace statement does.
---
Alternately, if you do all of the exceptional replacements first, then you should just be able to follow them with a catchall
```auto
$input_scalar =~ s/(
)(.*?)(<\/p>)/
$2<\/p>/g;
```
since there won’t be any of the exceptional values left to match.
Also, the (.\*?) in your regexp won’t match multiline constructs (e.g., where the \ and \ tags are on separate lines) unless you use the /s modifier. You may want to use /i as well (or [Pp]), if the tags might be \…\.
Something I find useful for these quick search-and-replace operations is perl -pe \ \. This sets $\_ equal to each line of \ and runs \ on it, then prints the result, so you can try different things quickly. When you get it to work, use perl -p -i.bak -e, which then saves the original file as \.bak and puts the modifications in \.
---
> [@Omphaloskeptic](#):
>
> Alternately, if you do all of the exceptional replacements first, then you should just be able to follow them with a catchall
>
> ```auto
>
> $input_scalar =~ s/(
)(.*?)(<\/p>)/
$2<\/p>/g;
>
> ```
>
> since there won’t be any of the exceptional values left to match.
>
> Also, the (.\*?) in your regexp won’t match multiline constructs (e.g., where the \ and \ tags are on separate lines) unless you use the /s modifier. You may want to use /i as well (or [Pp]), if the tags might be \…\.
>
> Something I find useful for these quick search-and-replace operations is perl -pe \ \. This sets $\_ equal to each line of \ and runs \ on it, then prints the result, so you can try different things quickly. When you get it to work, use perl -p -i.bak -e, which then saves the original file as \.bak and puts the modifications in \.
Thanks **Omphaloskeptic**. I was doing **perl -pe** at first, but I couldn’t get it to work with multiple lines (as you mention), so I switched to a full perl program. Then I realized I didn’t really WANT my file to be multiline, so I consolidated it so that every statement in the HTML file is on a single line, separated by two CR-LF’s, and just turned on line wrapping in my editor. That way I didn’t have to ever worry about the multiline problem. I appreciate the extra information for the future, though – undoubtedly it will come in handy at some point, probably soon.