Use the 'x' modifier:

m/
    (?<=a)   # positive lookbehind for 'a'
    sd       # literal 'sd'
    [^e]     # ensure there isn't an 'e' here
/x;

[download]

To help troubleshoot, you can set use re 'debug';, or use YAPE::Regex::Explain.

You might be inclined to show the regex, a bit of surrounding code, and a sample of your data, as there may be more efficient/cleaner ways to do this instead of using one long regex. We won't know though unless you provide more details.

-stevieb

In reply to Re: Break a long regex across multiple lines of code, with comments by stevieb
in thread Break a long regex across multiple lines of code, with comments by davidfilmer

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