X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlretut.pod;h=be4693dd0f87723a3cf525a45142d9ec5cd4d2f2;hb=8927c9d824bf5d960d90467f403bdfa9cbaff854;hp=4ea9ecc497a48d3b38c3c826050f09a061bc5431;hpb=1d81abf3fba4f3e6fcf1c6245d196a5c4fbf4d19;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlretut.pod b/pod/perlretut.pod index 4ea9ecc..be4693d 100644 --- a/pod/perlretut.pod +++ b/pod/perlretut.pod @@ -158,13 +158,14 @@ that a metacharacter can be matched by putting a backslash before it: "2+2=4" =~ /2\+2/; # matches, \+ is treated like an ordinary + "The interval is [0,1)." =~ /[0,1)./ # is a syntax error! "The interval is [0,1)." =~ /\[0,1\)\./ # matches - "/usr/bin/perl" =~ /\/usr\/local\/bin\/perl/; # matches + "/usr/bin/perl" =~ /\/usr\/bin\/perl/; # matches In the last regexp, the forward slash C<'/'> is also backslashed, because it is used to delimit the regexp. This can lead to LTS (leaning toothpick syndrome), however, and it is often more readable to change delimiters. + "/usr/bin/perl" =~ m!/usr/bin/perl!; # easier to read The backslash character C<'\'> is a metacharacter itself and needs to be backslashed: @@ -689,10 +690,11 @@ inside goes into the special variables C<$1>, C<$2>, etc. They can be used just as ordinary variables: # extract hours, minutes, seconds - $time =~ /(\d\d):(\d\d):(\d\d)/; # match hh:mm:ss format - $hours = $1; - $minutes = $2; - $seconds = $3; + if ($time =~ /(\d\d):(\d\d):(\d\d)/) { # match hh:mm:ss format + $hours = $1; + $minutes = $2; + $seconds = $3; + } Now, we know that in scalar context, S > returns a true or false @@ -1403,7 +1405,8 @@ off. C<\G> allows us to easily do context-sensitive matching: The combination of C and C<\G> allows us to process the string a bit at a time and use arbitrary Perl logic to decide what to do next. -Currently, the C<\G> anchor only works at the beginning of a pattern. +Currently, the C<\G> anchor is only fully supported when used to anchor +to the start of the pattern. C<\G> is also invaluable in processing fixed length records with regexps. Suppose we have a snippet of coding region DNA, encoded as @@ -1706,7 +1709,7 @@ it matches I byte 0-255. So The last regexp matches, but is dangerous because the string I position is no longer synchronized to the string I position. This generates the warning 'Malformed UTF-8 -character'. C<\C> is best used for matching the binary data in strings +character'. The C<\C> is best used for matching the binary data in strings with binary data intermixed with Unicode characters. Let us now discuss the rest of the character classes. Just as with @@ -2003,6 +2006,10 @@ They evaluate true if the regexps do I match: $x =~ /foo(?!baz)/; # matches, 'baz' doesn't follow 'foo' $x =~ /(? is unsupported in lookbehind, because the already +treacherous definition of C<\C> would become even more so +when going backwards. + =head2 Using independent subexpressions to prevent backtracking The last few extended patterns in this tutorial are experimental as of