Re: Regex Search String in a Variable

You seem to understand this already, but I thought I'd try to make it clear for future readers of this thread: Why doesn't it work?

When you finish slashing away at the $search string, what have you got?

Win8 Strawberry 5.8.9.5 (32)  Sat 05/01/2021 17:03:44
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -l

my $search = "x2\\.+\\x4";
print $search;

^Z
x2\.+\x4
  ^^
  ||
  ++----- backslash escaped literal period (one or more)
[download]

Unescaped, the . (dot) is a regex matching operator (see perlre, perlretut). Escaped, it matches a literal period, and there is no period to match in your example $text string. The + quantifier matches one or more of the atom before it, a literal period in this case.

Similar result if you pass the $search string through the qr// regex object constructor.

Win8 Strawberry 5.8.9.5 (32)  Sat 05/01/2021 17:14:10
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -l

my $search = "x2\\.+\\x4";
my $rx_search = qr/$search/;
print $rx_search;

^Z
(?-xism:x2\.+\x4)
[download]

Update: Minor re-formatting for clarity/coherence.

Give a man a fish: <%-{-{-{-<

Comment on Re: Regex Search String in a Variable Select or Download Code

Replies are listed 'Best First'.
Re^2: Regex Search String in a Variable by LanX (Saint) on May 02, 2021 at 12:07 UTC
I think the easiest way to put it, is that backslash is the escape character for literal strings as well as for regex meta-characters. This means they need to be doubled for each step. Even in single quoted strings, since they allow escaping the delimiter. AFAIK are here-docs the only way to avoid the need of self-escaping a `\` Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]
Re^3: Regex Search String in a Variable by AnomalousMonk (Archbishop) on May 03, 2021 at 01:22 UTC
AFAIK are here-docs the only way to avoid the need of self-escaping a \ Actually, I was not aware of this, but yeah: `Win8 Strawberry 5.8.9.5 (32) Sun 05/02/2021 21:06:46 C:\@Work\Perl\monks >perl -Mstrict -Mwarnings my $s = <<'EOT'; \b\\o\\\f\\\\f\ EOT print "'$s' \n"; $s = q/\q\\u\\\u\\\\x\ /; print "'$s' \n"; ^Z '\b\\o\\\f\\\\f\ ' '\q\u\\u\\x\ '` [download] Learned something today! :) Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re^4: Regex Search String in a Variable by LanX (Saint) on May 03, 2021 at 12:37 UTC
Well it's like reading a doc (sic), just w/o needing a filehandle. Alas we need to chomp it to get rid of a newline. Putting it in the `__DATA__` section would do as well, but this is reading from an filehandle, but w/o need to open it first. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]