end of line anchor in regex

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Re: end of line anchor in regex by FunkyMonk (Chancellor) on Dec 09, 2007 at 16:20 UTC
You can use the `/m` modifier to make $ match newlines: `$text =~ s/hello$//gm;` See perlre for more information	[reply] [d/l] [select]
Re: end of line anchor in regex by jrsimmon (Hermit) on Dec 09, 2007 at 16:12 UTC
There's nothing wrong with your substitution. You're string doesn't end with the word "hello", so it doesn't match and no substitution is made.	[reply]
Re: end of line anchor in regex by dwm042 (Priest) on Dec 09, 2007 at 16:50 UTC
As others have already pointed out, the variable $text doesn't end in 'hello', so the substitution never occurs. If you reorganized the program so that the data were read in from a file, or from a __DATA___ statement following the program, it works just fine, as so: `#!/usr/bin/perl use warnings; use strict; while (my $text = <DATA>) { $text =~ s/hello$//g; print $text; } __DATA__ hello world` [download] The output is: `~/perl/perlmonks$ ./nohello.pl world` [download]	[reply] [d/l] [select]
Re: end of line anchor in regex by ikegami (Patriarch) on Dec 09, 2007 at 18:52 UTC
By default (no "m" option), `$` matches at a newline at the end of the string. `$` matches at the end of the string. With the "m" option (`s///m`), `$` matches at the end of a line (at a newline). `$` matches at the end of the string.	[reply] [d/l] [select]
Re: end of line anchor in regex by sh1tn (Priest) on Dec 09, 2007 at 17:39 UTC
Less efficient, still possible: `$text = join($1, grep(/[^hello]/, split(/(\n)/, $text)));` [download] perlrequick, perlretut, split, grep, join.	[reply] [d/l]
Re^2: end of line anchor in regex by Anonymous Monk on Dec 09, 2007 at 18:34 UTC
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: { }` [download] 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)?	[reply] [d/l] [select]
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]
Re^2: end of line anchor in regex by ikegami (Patriarch) on Dec 10, 2007 at 04:37 UTC
Captures in the `split` regex does have an effect, but setting `$1` shouldn't be relied on. The effect of captures in the `split` regex is to return the captured data. `split(/\n/, "hello\nworld") -> ("hello", "world") split(/(\n)/, "hello\nworld") -> ("hello", "\n", "world")` [download] I'd recommend `$text = join '', grep $_ ne "$word\n", split /(?<=\n)/, $text;` [download] if you wanted to use `split`.	[reply] [d/l] [select]