X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlop.pod;h=0bb506ddc708ada8a8988131bf1243676f097a0d;hb=0e06870bf080a38cda51c06c6612359afc2334e1;hp=ac9d4b65da8c3bf1b30f1c2adeaa57fac0777542;hpb=61eff3bce55f37db01a97cd993ca4e73fb953a10;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlop.pod b/pod/perlop.pod index ac9d4b6..0bb506d 100644 --- a/pod/perlop.pod +++ b/pod/perlop.pod @@ -119,7 +119,7 @@ you increment a variable that is numeric, or that has ever been used in a numeric context, you get a normal increment. If, however, the variable has been used in only string contexts since it was set, and has a value that is not the empty string and matches the pattern -C, the increment is done as a string, preserving each +C, the increment is done as a string, preserving each character within its range, with carry: print ++($foo = '99'); # prints '100' @@ -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, +$_. When used in scalar context, the return value generally indicates the +success of the operation. Behavior in list context depends on the particular +operator. See L for details. + +If the right argument is an expression rather than a search pattern, substitution, or transliteration, it is interpreted as a search pattern at run time. This can be less efficient than an explicit search, because the pattern must be compiled every time the expression is evaluated. @@ -193,7 +196,7 @@ C<$a> minus the largest multiple of C<$b> that is not greater than C<$a>. If C<$b> is negative, then C<$a % $b> is C<$a> minus the smallest multiple of C<$b> that is not less than C<$a> (i.e. the result will be less than or equal to zero). -Note than when C is in scope, "%" give you direct access +Note than when C is in scope, "%" gives you direct access to the modulus operator as implemented by your C compiler. This operator is not as well defined for negative operands, but it will execute faster. @@ -296,7 +299,14 @@ to the right argument. Binary "<=>" returns -1, 0, or 1 depending on whether the left argument is numerically less than, equal to, or greater than the right -argument. +argument. If your platform supports NaNs (not-a-numbers) as numeric +values, using them with "<=>" returns undef. NaN is not "<", "==", ">", +"<=" or ">=" anything (even NaN), so those 5 return false. NaN != NaN +returns true, as does NaN != anything else. If your platform doesn't +support NaNs then NaN is just a string with numeric value 0. + + perl -le '$a = NaN; print "No NaN support here" if $a == $a' + perl -le '$a = NaN; print "NaN support here" if $a != $a' Binary "eq" returns true if the left argument is stringwise equal to the right argument. @@ -304,8 +314,9 @@ the right argument. Binary "ne" returns true if the left argument is stringwise not equal to the right argument. -Binary "cmp" returns -1, 0, or 1 depending on whether the left argument is stringwise -less than, equal to, or greater than the right argument. +Binary "cmp" returns -1, 0, or 1 depending on whether the left +argument is stringwise less than, equal to, or greater than the right +argument. "lt", "le", "ge", "gt" and "cmp" use the collation (sort) order specified by the current locale if C is in effect. See L. @@ -704,7 +715,7 @@ on a Mac, these are reversed, and on systems without line terminator, printing C<"\n"> may emit no actual data. In general, use C<"\n"> when you mean a "newline" for your system, but use the literal ASCII when you need an exact character. For example, most networking protocols expect -and prefer a CR+LF (C<"\012\015"> or C<"\cJ\cM">) for line terminators, +and prefer a CR+LF (C<"\015\012"> or C<"\cM\cJ">) for line terminators, and although they often accept just C<"\012">, they seldom tolerate just C<"\015">. If you get in the habit of using C<"\n"> for networking, you may be burned some day. @@ -785,14 +796,14 @@ If "'" is the delimiter, no interpolation is performed on the PATTERN. PATTERN may contain variables, which will be interpolated (and the pattern recompiled) every time the pattern search is evaluated, except -for when the delimiter is a single quote. (Note that C<$)> 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 the life of the script. However, mentioning C constitutes a promise that you won't change the variables in the pattern. If you change them, -Perl won't even notice. See also L<"qr//">. +Perl won't even notice. See also L<"qr/STRING/imosx">. If the PATTERN evaluates to the empty string, the last I matched regular expression is used instead. @@ -845,9 +856,11 @@ string also resets the search position. You can intermix C matches with C, where C<\G> is a zero-width assertion that matches the exact position where the previous -C, if any, left off. The C<\G> assertion is not supported without -the C modifier. (Currently, without C, C<\G> behaves just like -C<\A>, but that's accidental and may change in the future.) +C, if any, left off. Without the C modifier, the C<\G> assertion +still anchors at pos(), but the match is of course only attempted once. +Using C<\G> without C on a target string that has not previously had a +C match applied to it is the same as using the C<\A> assertion to match +the beginning of the string. Examples: @@ -855,7 +868,7 @@ Examples: ($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g); # scalar context - $/ = ""; $* = 1; # $* deprecated in modern perls + $/ = ""; while (defined($paragraph = <>)) { while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) { $sentences++; @@ -873,6 +886,7 @@ Examples: print "3: '"; print $1 while /(p)/gc; print "', pos=", pos, "\n"; } + print "Final: '$1', pos=",pos,"\n" if /\G(.)/; The last example should print: @@ -882,6 +896,13 @@ The last example should print: 1: '', pos=7 2: 'q', pos=8 3: '', pos=8 + Final: 'q', pos=8 + +Notice that the final match matched C instead of C

, which a match +without the C<\G> anchor would have done. Also note that the final match +did not update C -- C is only updated on a C match. If the +final match did indeed match C

, it's a good bet that you're running an +older (pre-5.6.0) Perl. A useful idiom for C-like scanners is C. You can combine several regexps like this to process a string part-by-part, @@ -935,7 +956,7 @@ A double-quoted, interpolated string. =item qr/STRING/imosx -This operators quotes--and compiles--its I as a regular +This operator quotes (and possibly compiles) its I as a regular expression. I is interpolated the same way as I in C. If "'" is used as the delimiter, no interpolation is done. Returns a Perl value which may be used instead of the @@ -994,13 +1015,14 @@ for a detailed look at the semantics of regular expressions. =item `STRING` -A string which is (possibly) interpolated and then executed as a system -command with C or its equivalent. Shell wildcards, pipes, -and redirections will be honored. The collected standard output of the -command is returned; standard error is unaffected. In scalar context, -it comes back as a single (potentially multi-line) string. In list -context, returns a list of lines (however you've defined lines with $/ -or $INPUT_RECORD_SEPARATOR). +A string which is (possibly) interpolated and then executed as a +system command with C or its equivalent. Shell wildcards, +pipes, and redirections will be honored. The collected standard +output of the command is returned; standard error is unaffected. In +scalar context, it comes back as a single (potentially multi-line) +string, or undef if the command failed. In list context, returns a +list of lines (however you've defined lines with $/ or +$INPUT_RECORD_SEPARATOR), or an empty list if the command failed. Because backticks do not affect standard error, use shell file descriptor syntax (assuming the shell supports this) if you care to address this. @@ -1048,6 +1070,12 @@ 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 +1116,8 @@ 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 +1159,10 @@ 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 +1189,12 @@ 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+)/$1/eeg; # Delete (most) C comments. @@ -1193,9 +1226,9 @@ to occur that you might want. Here are two common cases: # expand tabs to 8-column spacing 1 while s/\t+/' ' x (length($&)*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 +1244,12 @@ 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 +1262,6 @@ 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 +1279,6 @@ 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: $ARGV[1] =~ tr/A-Z/a-z/; # canonicalize to lower case @@ -1265,9 +1298,6 @@ Examples: tr [\200-\377] [\000-\177]; # delete 8th bit - tr/\0-\xFF//CU; # change Latin-1 to Unicode - tr/\0-\x{FF}//UC; # change Unicode to Latin-1 - If multiple transliterations are given for a character, only the first one is used: @@ -1313,7 +1343,7 @@ their results are the same, we consider them individually. For different quoting constructs, Perl performs different numbers of passes, from one to five, but these passes are always performed in the same order. -=over +=over 4 =item Finding the end @@ -1367,7 +1397,7 @@ used in parsing. The next step is interpolation in the text obtained, which is now delimiter-independent. There are four different cases. -=over +=over 4 =item C<<<'EOF'>, C, C, C, C @@ -1398,7 +1428,7 @@ as C<"\\\t"> (since TAB is not alphanumeric). Note also that: may be closer to the conjectural I of the writer of C<"\Q\t\E">. Interpolated scalars and arrays are converted internally to the C and -C<.> catentation operations. Thus, C<"$foo XXX '@arr'"> becomes: +C<.> catenation operations. Thus, C<"$foo XXX '@arr'"> becomes: $foo . " XXX '" . (join $", @arr) . "'"; @@ -1449,8 +1479,8 @@ 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 +1541,7 @@ 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 +1618,8 @@ 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 +1747,7 @@ 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 @@ -1796,22 +1827,6 @@ operation you intend by using C<""> or C<0+>, as in the examples below. See L for information on how to manipulate individual bits in a bit vector. -=head2 Strings of Character - -A literal of the form C is parsed as a string composed -of characters with the specified ordinals. This provides an alternative, -more readable way to construct strings, rather than use the somewhat less -readable interpolation form C<"\x{1}\x{14}\x{12c}\x{fa0}">. This is useful -for representing Unicode strings, and for comparing version "numbers" -using the string comparison operators, C, C, C etc. - -If there are two or more dots in the literal, the leading C may be -omitted. - -Such literals are accepted by both C and C for doing a version -check. The C<$^V> special variable also contains the running Perl -interpreter's version in this form. See L. - =head2 Integer Arithmetic By default, Perl assumes that it must do most of its arithmetic in @@ -1832,8 +1847,8 @@ integer>, if you take the C, you'll still get C<1.4142135623731> or so. Used on numbers, the bitwise operators ("&", "|", "^", "~", "<<", -and ">>") always produce integral results. (But see also L.) However, C still has meaning for +and ">>") always produce integral results. (But see also +L.) However, C still has meaning for them. By default, their results are interpreted as unsigned integers, but if C is in effect, their results are interpreted as signed integers. For example, C<~0> usually evaluates to a large