Re^3: Regex stored in a scalar

True, it won't work this way, but this quick test under the Perl debugger show that it might be feasible with a slight syntax tweak and one further step to process it. Here, I am passing the replacement string with \n to my debugger session:

$ perl -de 42 foo\\n

Loading DB routines from perl5db.pl version 1.33
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(-e:1):   42
  DB<1> $c = shift;

  DB<2> x $c
0  'foo\\n'
  DB<3> $c =~ s|\\n|\n|;

  DB<4> x $c
0  'foo
'
  DB<5>
[download]

So, this seems to work, although it might not be the most elegant construct. Of course, it also assumes that you know when writing your program beforehand, you might need some newline characters to be reprocessed.

Comment on Re^3: Regex stored in a scalar Select or Download Code

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Re^4: Regex stored in a scalar by AnomalousMonk (Archbishop) on Aug 22, 2015 at 18:15 UTC
I can't see how to enter that with `my $subst = <STDIN>;` True, it won't work this way ... it might be feasible with a slight syntax tweak and one further step to process it ... assumes that you know ... you might need some newline characters to be reprocessed As long as you can get `\nything` into a scalar, you can search/replace with it, and a statement like `my $subst = <STDIN>;` is perfectly adequate to capture any sequence with a literal backslash in it: `c:\@Work\Perl>perl -wMstrict -e "print 'enter a string: '; my $string = <STDIN>; chomp $string; print qq{'$string' \n}; " enter a string: )\n( ')\n('` [download] (Caveat: Actually, I can only test this under Windoze; there may be OSen that mung backslashes in situations like this.) Once you have captured a string with a backslash, you can use it for search/replace straightforwardly: c:\@Work\Perl>perl -wMstrict -le "printf 'enter search regex: '; my $search = <STDIN>; chomp $search; ;; printf 'enter replacement string: '; my $replace = <STDIN>; chomp $replace; ;; print qq{doing s/$search/$replace/}; ;; my $s = qq{as\ngh\njk}; printf qq{%s: '$s' \n}, 7, 'initial'; ;; my @regex = ( { lh => $search, rh => $replace, }, ); ;; for my $hr_s (@regex) { $s =~ s[ (?-x)$hr_s->{lh}]{ qq{qq{$hr_s->{rh}}} }xmsgee; } ;; printf qq{%s: '$s' \n}, 7, 'final'; " enter search regex: \n enter replacement string: __\n__ doing s/\n/__\n__/ initial: 'as gh jk' final: 'as__ __gh__ __jk' [download] (This is essentially the example code from below.) Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^5: Regex stored in a scalar by Laurent_R (Canon) on Aug 22, 2015 at 18:53 UTC
Agreed, but my only point was that, under Unix, if you enter `"foo\n"` at STDIN or at the command line, the backslash is lost and you get `"foon"` into your variable. So I needed to put two backslashes, meaning that I then needed to change from the string `"\\n"` to the newline character "\n" to get the replacement string `"foo\n"` I was looking for. There might be a better way, but at least I was showing that this was possible. So, in effect, we are saying almost the same thing, I believe. Escaping and quoting rules are not exactly identical in Perl and in Unix (and also not under Windows), so it can get a bit contrived (and not portable) exactly to get what you want.	[reply] [d/l] [select]