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Editorial Team
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Asked: 2026-05-16T07:02:26+00:00

I need a regular expression to uncomment a block of Perl code, commented with

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I need a regular expression to uncomment a block of Perl code, commented with # in each line.

As of now, my find expression in the Eclipse IDE is (^#(.*$\R)+) which matches the commented block, but if I give $2 as the replace expression, it only prints the last matched line. How do I remove the # while replacing?

For example, I need to convert:

# print "yes";
# print "no";
# print "blah";

to

print "yes";
print "no";
print "blah";
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1 Answer

  1. Editorial Team

    In most flavors, when a capturing group is repeated, only the last capture is kept. Your original pattern uses + repetition to match multiple lines of comments, but group 2 can only keep what was captured in the last match from the last line. This is the source of your problem.

    To fix this, you can remove the outer repetition, so you match and replace one line at a time. Perhaps the simplest pattern to do this is to match:

    ^#\s*

    And replace with the empty string.

    Since this performs match and replacement one line at a time, you must repeat it as many times as necessary (in some flavors, you can use the g global flag, in e.g. Java there are replaceFirst/All pair of methods instead).

    References

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    Special note on Eclipse keyboard shortcuts

    It Java mode, Eclipse already has keyboard shortcuts to add/remove/toggle block comments. By default, Ctrl+/ binds to the “Toggle comment” action. You can highlight multiple lines, and hit Ctrl+/ to toggle block comments (i.e. //) on and off.

    You can hit Ctrl+Shift+L to see a list of all keyboard shortcuts. There may be one in Perl mode to toggle Perl block comments #.

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