Re^2: end of line anchor in regex

less efficient, less maintainable, with a warning, and with a pitfall: what if a word other than the word to be deleted is composed entirely of letters in the targeted word. e.g.:

perl -wMstrict -e "my $text = qq(start\nrats\n);
$text = join($1, grep(/[^start]/, split(/(\n)/, $text)));
print qq(o/p: \n);  print qq({$text})"
Use of uninitialized value in join or string at -e line 1.
o/p:
{

}
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wouldn't it at least be better to say grep($_ ne 'start', ... ) (although it still leaves the "Use of uninitialized value ..." problem, which i don't quite understand)?

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Re^3: end of line anchor in regex by Anonymous Monk on Dec 10, 2007 at 04:09 UTC
...although it still leaves the "Use of uninitialized value ..." problem, which i don't quite understand. my confusion stemmed from my bemusement with an imagined connection between the `(\n)` expression in the `split` regex and the `$1` capture variable in the `join` and the idea that `$1` must contain a newline at that point. then it occurred to me that the intervening `grep` regex would undefine all the capture variables and, since it had no capturing parentheses of its own, leave them that way. but it goes beyond that. apparently, "capturing" parentheses in a `split` regex don't actually capture (at least not to the capture variables), so `$1` was never defined at any point. `perl -wMstrict -e "my @ra = split /(c)/, 'abcde'; print '$1 ', defined $1 ? 'defined' : 'undefined', qq( @ra)" $1 undefined ab c de` [download]	[reply] [d/l] [select]

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Re^3: end of line anchor in regex
by Anonymous Monk on Dec 10, 2007 at 04:09 UTC

...although it still leaves the "Use of uninitialized value ..." problem, which i don't quite understand.

(\n)

split

$1

join

$1

then it occurred to me that the intervening grep regex would undefine all the capture variables and, since it had no capturing parentheses of its own, leave them that way.

but it goes beyond that. apparently, "capturing" parentheses in a split regex don't actually capture (at least not to the capture variables), so $1 was never defined at any point.

perl -wMstrict -e "my @ra = split /(c)/, 'abcde';
print '$1 ', defined $1 ? 'defined' : 'undefined', qq( @ra)"
$1 undefined ab c de
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