substr on $

gisrob has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: substr on $_ by japhy (Canon) on Sep 28, 2001 at 00:31 UTC
After seeing the suggested regexes, I'm going to offer a slight change: `s/\d+(\d\d)\./$1/; # no need for the (\d+) at the end # being replaced by $2 (itself!)` [download] _____________________________________________________ Jeff`[japhy]`Pinyan: Perl, regex, and perl hacker. `s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;`	[reply] [d/l]
Re: Re: substr on $_ by Anonymous Monk on Sep 28, 2001 at 02:20 UTC
Alternatively, no need to capture anything. Although alternation is generally an efficiency pig, for these small strings it tests a bit quicker. `s/^\d\d\|\.//g;` [download]	[reply] [d/l]
Re: substr on $_ by Ovid (Cardinal) on Sep 28, 2001 at 00:15 UTC
`perl -pi.bak -e 's/\d\d(\d\d)\.(\d{5})/$1$2/' somefile.txt` [download] Cheers, Ovid Update: Sheesh. `japhy's` reply made me feel stupid :) `perl -pi.bak -e 's/\d\d(\d\d)\./$1/' somefile.txt` [download] Vote for paco! Join the Perlmonks Setiathome Group or just click on the the link and check out our stats.	[reply] [d/l] [select]
(crazyinsomniac: shock) Re: substr on $_ by crazyinsomniac (Prior) on Sep 28, 2001 at 12:02 UTC
I am shocked and amazed to hear such blasphemy. The title of the node is "substr on $_ by gisrob" yet all I see is variations of `$new = s/\d+.\d/replacement/g;`. Talk about a shared mentality, didn't anyone notice the word substr?? No, it's not just gibberish, it is an actual perl function. Observe: `#!/usr/bin/perl -w use strict; while(<DATA>) { my $dot_ix = index $_ ,'.'; printf "%40s: %s\n", "the string before trimming", $_; printf "%40s: %s\n", "dot+", substr $_, $dot_ix; printf "%40s: %s\n", "dot-2", substr($_, $dot_ix - 2); printf "%40s: %s\n", "trimmed fat", substr($_, $dot_ix - 2, $dot_ix -1, ''); # $dot_ix -1 since it's the num of chars, not index printf "%40s: %s\n", "the string after trimming", $_; } __END__ 1996.40637 1996.41064 1996.41199 1996.41467 1996.41882` [download] And the output: F:\dev>perl sub.pl the string before trimming: 1996.40637 dot+: .40637 dot-2: 96.40637 trimmed fat: 96. the string after trimming: 1940637 the string before trimming: 1996.41064 dot+: .41064 dot-2: 96.41064 trimmed fat: 96. the string after trimming: 1941064 the string before trimming: 1996.41199 dot+: .41199 dot-2: 96.41199 trimmed fat: 96. the string after trimming: 1941199 the string before trimming: 1996.41467 dot+: .41467 dot-2: 96.41467 trimmed fat: 96. the string after trimming: 1941467 the string before trimming: 1996.41882 dot+: .41882 dot-2: 96.41882 trimmed fat: 96. the string after trimming: 1941882 UPDATE: OOps, I think funny ;D #!/usr/bin/perl -w use strict; while(<DATA>) { my $dot_ix = index $_ ,'.'; printf "%40s: %s\n", "the string before trimming", $_; printf "%40s: %s\n", "dot+", substr $_, $dot_ix; # oops, i think funny # printf "%40s: %s\n", # "dot-2", # substr($_, $dot_ix - 2); printf "%40s: %s\n", "string - 2", substr($_, 2); # printf "%40s: %s\n", # "trimmed fat", # substr($_, $dot_ix - 2, $dot_ix -1, ''); # # $dot_ix -1 since it's the num of chars, not index printf "%40s: %s\n", "trimmed fat", substr($_, $dot_ix, 1, ''); printf "%40s: %s\n", "trimmed fat", substr($_, 0, 2, ''); printf "%40s: %s\n", "the string after trimming", $_; } __END__ 1996.40637 1996.41064 1996.41199 1996.41467 1996.41882 [download] ___crazyinsomniac_______________________________________ `Disclaimer: Don't blame. It came from inside the void` `perl -e "$q=$_;map({chr unpack qq;H;,$_}split(q;;,qH*));print;$q/$q;"`	[reply] [d/l] [select]
Re: (crazyinsomniac: shock) Re: substr on $_ by danger (Priest) on Sep 28, 2001 at 14:08 UTC
Well, in order to appease crazyinsomniac's shock at the lack of substr() solutions, here's a fun little version: `#!/usr/bin/perl -w use strict; $_ = 'x' x 11; my($x,$y) = \(substr($_,2,2), substr($_,5)); while(<DATA>){ print $$x,$$y; } __END__ 1996.40637 1996.41064 1996.41199 1996.41467 1996.41882` [download]	[reply] [d/l]
(jeffa) Re: substr on $_ by jeffa (Bishop) on Sep 28, 2001 at 00:16 UTC
Here is one way: `use strict; # look ma! no $_! ;) while (<DATA>) { s/\d\d(\d\d)\.(\d+)/$1$2/; print; } __DATA__ 1996.40637 1996.41064 1996.41199 1996.41467 1996.41882` [download] UPDATE: ack! i see it now: you want =~, not = for your substitution lines. Here is my above while loop with the implicit $_: `while ($_ = <DATA>) { $_ =~ s/\d\d(\d\d)\.(\d+)/$1$2/; print $_; }` [download] UPDATE 2: re japhy DOH! ;) jeffa	[reply] [d/l] [select]
Re: (jeffa) Re: substr on $_ by gisrob (Novice) on Sep 28, 2001 at 00:47 UTC
Cool - thanks.	[reply]
Re: substr on $_ by virtualsue (Vicar) on Sep 28, 2001 at 17:39 UTC
I'm pretty big on checking the validity of the data that I get as well as doing the correct kind of actions with it. Perl is naturally magnificent at doing both in one fell swoop: `#!/usr/local/bin/perl -w use strict; while (my $val = <DATA>) { chomp $val; print "Read: $val - "; # Only accept input values which consist of NNNN.NNNNN, one per lin +e if ($val =~ s/^\d{2}(\d{2})\.(\d{5})$/$1$2/) { print "format OK, changed to $val.\n"; } else { print "item $val not in YYYY.NNNNN format.\n"; } } __DATA__ 1996.40637 1996.41064 1996.41199 1996.41467 1996.41882 11996.41882 1997.418828 1998.4128` [download]	[reply] [d/l]
Re: substr on $_ by dragonchild (Archbishop) on Sep 28, 2001 at 00:14 UTC
If you assign the results of a substition regex, that doesn't assign the new string. Regex substitutions are done in-place. The return value is the number of substitutions, not the new string. It sounds like you want to do too many operations on one line. You're not changed by the character, my friend! Just do your assignment, then your substitution. `my $new = $_; $new =~ s/foo/bar/g;` [download] ------ We are the carpenters and bricklayers of the Information Age. Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.	[reply] [d/l]