Re^3: Combining regexes

Further to some of BrowserUk's comments ++above:

A \ (backslash) within a \Q...\E sequence: if the backslash is included in the interpolated variable, things are simpler:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $curdir   = 'Y:\Music\Schubert\Lieder\Terfel';
 my $startdir = 'Y:\mUsIc\\';
 ;;
 my $plsname = $curdir;
 $plsname =~ s/^\Q$startdir\E//i;
 $plsname =~ s/\\/_/g;
 $plsname .= '.pls';
 print qq{'$plsname'};
"
'Schubert_Lieder_Terfel.pls'
[download]

(Note that the final \ (backslash) in the $startdir assignment has to be escaped because it's just before the closing single-quote delimiter.)

Some examples of my ($plsname) = $curdir =~ regex; (still not applicable):

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'bar foooo bozzle';
 ;;
 my ($capture) = $s =~ m{ (fo+) }xms;
 print qq{'$capture'};
 ;;
 my ($found_it) = $s =~ m{ (?<= \s) b .* e }xmsg;
 print qq{'$found_it'};
 ;;
 my $regex = qr{ \A (b \w+) }xms;
 my ($it_was_there) = $s =~ $regex;
 print qq{'$it_was_there'};
"
'foooo'
'bozzle'
'bar'
[download]

(The second example without explicit capture groups.) (Update: Changed code above to add $regex example.)

Also note that BrowserUk is very experienced at dealing with Big Data. If you're operating on a single string of a few dozen/hundred/thousand characters, the difference between s///g and tr/// will not be ~~detectable~~ | noticeable in practice.
As to docs, all the usual suspects: perlre, perlretut, perlrequick, perlrecharclass, perluniprops; in perlop: Quote and Quote-like Operators, Regexp Quote-Like Operators, Quote-Like Operators. (Update: Also see Pattern Matching, Regular Expressions, and Parsing in our very own Tutorials.)

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

Comment on Re^3: Combining regexes Select or Download Code

Replies are listed 'Best First'.
Re^4: Combining regexes by BrowserUk (Patriarch) on May 21, 2016 at 17:48 UTC
If you're operating on a single string of a few dozen/hundred/thousand characters, the difference between s///g and tr/// will not be detectable. Sorry, but that simply isn't true. For a 3 character string tr/// takes 1/3rd the time of starting up the regex engine. For a 30 character string, it is 1/8th the time. And by the time you get to just 300 characters, the regex engine is already 20 times slower for this task. $n = 1e0; cmpthese -1,{ a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ], b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] };; Rate b a b 1000796/s -- -60% a 2493375/s 149% -- $n = 1e1; cmpthese -1,{ a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ], b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] };; Rate b a b 234727/s -- -87% a 1838169/s 683% -- $n = 1e2; cmpthese -1,{ a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ], b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] };; Rate b a b 28926/s -- -95% a 585631/s 1925% -- $n = 1e3; cmpthese -1,{ a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y];], b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g;] };; Rate b a b 3087/s -- -96% a 76540/s 2379% -- [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :) In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^5: Combining regexes by AnomalousMonk (Archbishop) on May 21, 2016 at 17:58 UTC
... will not be detectable. I should have said "will not be noticeable in practice." In fact, I will say it... Give a man a fish: `<%-{-{-{-<`	[reply] [d/l]
Re^6: Combining regexes by BrowserUk (Patriarch) on May 21, 2016 at 18:05 UTC
I should have said "will not be noticeable in practice." In fact, I will say it... Agreed. But... Since there is no practical, clarity, nor conciseness advantage for this operation; why would you choose to use the less efficient over the more? Better methinks to get into the habit of thinking: 1 for 1 replacement of single chars, use tr///; than to have to always make a decision (or even investigate at what point) you should shift tack for this maneuverer. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :) In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^7: Combining regexes by AnomalousMonk (Archbishop) on May 21, 2016 at 18:47 UTC
Re^8: Combining regexes by Anonymous Monk on May 22, 2016 at 00:43 UTC