X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlop.pod;h=3c84e608019577152a60d6e74ec8237770c16025;hb=49b8b560b023159cf65bbcf3068dc24e8091bc05;hp=9c8fa23f1dac5b3c7b7077a9a26a4784ee0797f9;hpb=191d61a768175782efd32a263e82c70bcb0d1401;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlop.pod b/pod/perlop.pod index 9c8fa23..3c84e60 100644 --- a/pod/perlop.pod +++ b/pod/perlop.pod @@ -172,8 +172,11 @@ search or modify the string $_ by default. This operator makes that kind of operation work on some other string. The right argument is a search pattern, substitution, or transliteration. The left argument is what is supposed to be searched, substituted, or transliterated instead of the default -$_. The return value indicates the success of the operation. If the -right argument is an expression rather than a search pattern, +$_. When used in scalar context, the return value generally indicates the +success of the operation. Behavior in list context depends on the particular +operator. See L for details. + +If the right argument is an expression rather than a search pattern, substitution, or transliteration, it is interpreted as a search pattern at run time. This can be less efficient than an explicit search, because the pattern must be compiled every time the expression is evaluated. @@ -785,8 +788,8 @@ If "'" is the delimiter, no interpolation is performed on the PATTERN. PATTERN may contain variables, which will be interpolated (and the pattern recompiled) every time the pattern search is evaluated, except -for when the delimiter is a single quote. (Note that C<$)> and C<$|> -might not be interpolated because they look like end-of-string tests.) +for when the delimiter is a single quote. (Note that C<$(>, C<$)>, and +C<$|> are not interpolated because they look like end-of-string tests.) If you want such a pattern to be compiled only once, add a C after the trailing delimiter. This avoids expensive run-time recompilations, and is useful when the value you are interpolating won't change over @@ -1048,6 +1051,12 @@ multiple commands in a single line by separating them with the command separator character, if your shell supports that (e.g. C<;> on many Unix shells; C<&> on the Windows NT C shell). +Beginning with v5.6.0, Perl will attempt to flush all files opened for +output before starting the child process, but this may not be supported +on some platforms (see L). To be safe, you may need to set +C<$|> ($AUTOFLUSH in English) or call the C method of +C on any open handles. + Beware that some command shells may place restrictions on the length of the command line. You must ensure your strings don't exceed this limit after any necessary interpolations. See the platform-specific @@ -1088,8 +1097,8 @@ Some frequently seen examples: A common mistake is to try to separate the words with comma or to put comments into a multi-line C-string. For this reason, the -B<-w> switch (that is, the C<$^W> variable) produces warnings if -the STRING contains the "," or the "#" character. +C pragma and the B<-w> switch (that is, the C<$^W> variable) +produces warnings if the STRING contains the "," or the "#" character. =item s/PATTERN/REPLACEMENT/egimosx @@ -1131,9 +1140,10 @@ text is not evaluated as a command. If the PATTERN is delimited by bracketing quotes, the REPLACEMENT has its own pair of quotes, which may or may not be bracketing quotes, e.g., C or C<< s/bar/ >>. A C will cause the -replacement portion to be interpreted as a full-fledged Perl expression -and eval()ed right then and there. It is, however, syntax checked at -compile-time. +replacement portion to be treated as a full-fledged Perl expression +and evaluated right then and there. It is, however, syntax checked at +compile-time. A second C modifier will cause the replacement portion +to be Ced before being run as a Perl expression. Examples: @@ -1160,8 +1170,12 @@ Examples: # symbolic dereferencing s/\$(\w+)/${$1}/g; - # /e's can even nest; this will expand - # any embedded scalar variable (including lexicals) in $_ + # Add one to the value of any numbers in the string + s/(\d+)/1 + $1/eg; + + # This will expand any embedded scalar variable + # (including lexicals) in $_ : First $1 is interpolated + # to the variable name, and then evaluated s/(\$\w+)/$1/eeg; # Delete (most) C comments. @@ -1193,9 +1207,9 @@ to occur that you might want. Here are two common cases: # expand tabs to 8-column spacing 1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e; -=item tr/SEARCHLIST/REPLACEMENTLIST/cdsUC +=item tr/SEARCHLIST/REPLACEMENTLIST/cds -=item y/SEARCHLIST/REPLACEMENTLIST/cdsUC +=item y/SEARCHLIST/REPLACEMENTLIST/cds Transliterates all occurrences of the characters found in the search list with the corresponding character in the replacement list. It returns @@ -1211,6 +1225,12 @@ SEARCHLIST is delimited by bracketing quotes, the REPLACEMENTLIST has its own pair of quotes, which may or may not be bracketing quotes, e.g., C or C. +Note that C does B do regular expression character classes +such as C<\d> or C<[:lower:]>. The operator is not equivalent to +the tr(1) utility. If you want to map strings between lower/upper +cases, see L and L, and in general consider +using the C operator if you need regular expressions. + Note also that the whole range idea is rather unportable between character sets--and even within character sets they may cause results you probably didn't expect. A sound principle is to use only ranges @@ -1223,8 +1243,6 @@ Options: c Complement the SEARCHLIST. d Delete found but unreplaced characters. s Squash duplicate replaced characters. - U Translate to/from UTF-8. - C Translate to/from 8-bit char (octet). If the C modifier is specified, the SEARCHLIST character set is complemented. If the C modifier is specified, any characters @@ -1242,10 +1260,6 @@ enough. If the REPLACEMENTLIST is empty, the SEARCHLIST is replicated. This latter is useful for counting characters in a class or for squashing character sequences in a class. -The first C or C modifier applies to the left side of the translation. -The second one applies to the right side. If present, these modifiers override -the current utf8 state. - Examples: $ARGV[1] =~ tr/A-Z/a-z/; # canonicalize to lower case @@ -1265,9 +1279,6 @@ Examples: tr [\200-\377] [\000-\177]; # delete 8th bit - tr/\0-\xFF//CU; # change Latin-1 to Unicode - tr/\0-\x{FF}//UC; # change Unicode to Latin-1 - If multiple transliterations are given for a character, only the first one is used: @@ -1398,7 +1409,7 @@ as C<"\\\t"> (since TAB is not alphanumeric). Note also that: may be closer to the conjectural I of the writer of C<"\Q\t\E">. Interpolated scalars and arrays are converted internally to the C and -C<.> catentation operations. Thus, C<"$foo XXX '@arr'"> becomes: +C<.> catenation operations. Thus, C<"$foo XXX '@arr'"> becomes: $foo . " XXX '" . (join $", @arr) . "'"; @@ -1449,8 +1460,8 @@ the result is not predictable. It is at this step that C<\1> is begrudgingly converted to C<$1> in the replacement text of C to correct the incorrigible I hackers who haven't picked up the saner idiom yet. A warning -is emitted if the B<-w> command-line flag (that is, the C<$^W> variable) -was set. +is emitted if the C pragma or the B<-w> command-line flag +(that is, the C<$^W> variable) was set. The lack of processing of C<\\> creates specific restrictions on the post-processed text. If the delimiter is C, one cannot get @@ -1511,7 +1522,7 @@ terminator of a C<{}>-delimited construct. It is possible to inspect both the string given to RE engine and the resulting finite automaton. See the arguments C/C in the C> pragma, as well as Perl's B<-Dr> command-line -switch documented in L. +switch documented in L. =item Optimization of regular expressions @@ -1588,7 +1599,8 @@ to terminate the loop, they should be tested for explicitly: while () { last unless $_; ... } In other boolean contexts, C<< > >> without an -explicit C test or comparison elicit a warning if the B<-w> +explicit C test or comparison elicit a warning if the +C pragma or the B<-w> command-line switch (the C<$^W> variable) is in effect. The filehandles STDIN, STDOUT, and STDERR are predefined. (The @@ -1716,7 +1728,7 @@ A (file)glob evaluates its (embedded) argument only when it is starting a new list. All values must be read before it will start over. In list context, this isn't important because you automatically get them all anyway. However, in scalar context the operator returns -the next value each time it's called, or C +the next value each time it's called, or C when the list has run out. As with filehandle reads, an automatic C is generated when the glob occurs in the test part of a C, because legal glob returns (e.g. a file called F<0>) would otherwise