X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlop.pod;h=70fef4565b83ecf3bf4acde0d83383e2c85ad9fe;hb=a6a714bd63c892b02b99c5d9a11e90c9a061423b;hp=3c84e608019577152a60d6e74ec8237770c16025;hpb=84393cd974926732d8916ade7acf62979478deb1;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlop.pod b/pod/perlop.pod index 3c84e60..70fef45 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 ++($foo = '99'); # prints '100' @@ -196,7 +196,7 @@ C<$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. @@ -299,7 +299,9 @@ 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 "<=>" (or any other numeric comparison) +returns undef. Binary "eq" returns true if the left argument is stringwise equal to the right argument. @@ -307,8 +309,9 @@ 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. @@ -707,7 +710,7 @@ 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. @@ -795,7 +798,7 @@ 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. @@ -848,9 +851,11 @@ 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: @@ -858,7 +863,7 @@ 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++; @@ -876,6 +881,7 @@ 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: @@ -885,6 +891,13 @@ 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, @@ -938,7 +951,7 @@ 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 @@ -997,13 +1010,14 @@ 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. @@ -1324,7 +1338,7 @@ 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 @@ -1378,7 +1392,7 @@ 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 @@ -1828,8 +1842,8 @@ 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