precedence version of this.
X<!>
-Unary "-" performs arithmetic negation if the operand is numeric. If
-the operand is an identifier, a string consisting of a minus sign
-concatenated with the identifier is returned. Otherwise, if the string
-starts with a plus or minus, a string starting with the opposite sign
-is returned. One effect of these rules is that -bareword is equivalent
+Unary "-" performs arithmetic negation if the operand is numeric,
+including any string that looks like a number. If the operand is
+an identifier, a string consisting of a minus sign concatenated
+with the identifier is returned. Otherwise, if the string starts
+with a plus or minus, a string starting with the opposite sign is
+returned. One effect of these rules is that -bareword is equivalent
to the string "-bareword". If, however, the string begins with a
non-alphabetic character (excluding "+" or "-"), Perl will attempt to convert
the string to a numeric and the arithmetic negation is performed. If the
pattern, substitution, or transliteration. The left argument is what is
supposed to be searched, substituted, or transliterated instead of the default
$_. When used in scalar context, the return value generally indicates the
-success of the operation. Behavior in list context depends on the particular
-operator. See L</"Regexp Quote-Like Operators"> for details and
-L<perlretut> for examples using these operators.
+success of the operation. The exceptions are substitution (s///)
+and transliteration (y///) with the C</r> (non-destructive) option,
+which cause the B<r>eturn value to be the result of the substitution.
+Behavior in list context depends on the particular operator.
+See L</"Regexp Quote-Like Operators"> for details and L<perlretut> for
+examples using these operators.
If the right argument is an expression rather than a search pattern,
substitution, or transliteration, it is interpreted as a search pattern at run
Binary "!~" is just like "=~" except the return value is negated in
the logical sense.
+Binary "!~" with a non-destructive substitution (s///r) or transliteration
+(y///r) is a syntax error.
+
=head2 Multiplicative Operators
X<operator, multiplicative>
to its C-style or. In fact, it's exactly the same as C<||>, except that it
tests the left hand side's definedness instead of its truth. Thus, C<$a // $b>
is similar to C<defined($a) || $b> (except that it returns the value of C<$a>
-rather than the value of C<defined($a)>) and is exactly equivalent to
-C<defined($a) ? $a : $b>. This is very useful for providing default values
-for variables. If you actually want to test if at least one of C<$a> and
-C<$b> is defined, use C<defined($a // $b)>.
+rather than the value of C<defined($a)>) and yields the same result as
+C<defined($a) ? $a : $b> (except that the ternary-operator form can be
+used as a lvalue, while C<$a // $b> cannot). This is very useful for
+providing default values for variables. If you actually want to test if
+at least one of C<$a> and C<$b> is defined, use C<defined($a // $b)>.
The C<||>, C<//> and C<&&> operators return the last value evaluated
(unlike C's C<||> and C<&&>, which return 0 or 1). Thus, a reasonably
# code
}
-The range operator also works on strings, using the magical auto-increment,
-see below.
+The range operator also works on strings, using the magical
+auto-increment, see below.
In scalar context, ".." returns a boolean value. The operator is
-bistable, like a flip-flop, and emulates the line-range (comma) operator
-of B<sed>, B<awk>, and various editors. Each ".." operator maintains its
-own boolean state. It is false as long as its left operand is false.
+bistable, like a flip-flop, and emulates the line-range (comma)
+operator of B<sed>, B<awk>, and various editors. Each ".." operator
+maintains its own boolean state, even across calls to a subroutine
+that contains it. It is false as long as its left operand is false.
Once the left operand is true, the range operator stays true until the
right operand is true, I<AFTER> which the range operator becomes false
-again. It doesn't become false till the next time the range operator is
-evaluated. It can test the right operand and become false on the same
-evaluation it became true (as in B<awk>), but it still returns true once.
-If you don't want it to test the right operand until the next
-evaluation, as in B<sed>, just use three dots ("...") instead of
+again. It doesn't become false till the next time the range operator
+is evaluated. It can test the right operand and become false on the
+same evaluation it became true (as in B<awk>), but it still returns
+true once. If you don't want it to test the right operand until the
+next evaluation, as in B<sed>, just use three dots ("...") instead of
two. In all other regards, "..." behaves just like ".." does.
The right operand is not evaluated while the operator is in the
"false" state, and the left operand is not evaluated while the
operator is in the "true" state. The precedence is a little lower
than || and &&. The value returned is either the empty string for
-false, or a sequence number (beginning with 1) for true. The
-sequence number is reset for each range encountered. The final
-sequence number in a range has the string "E0" appended to it, which
-doesn't affect its numeric value, but gives you something to search
-for if you want to exclude the endpoint. You can exclude the
-beginning point by waiting for the sequence number to be greater
-than 1.
+false, or a sequence number (beginning with 1) for true. The sequence
+number is reset for each range encountered. The final sequence number
+in a range has the string "E0" appended to it, which doesn't affect
+its numeric value, but gives you something to search for if you want
+to exclude the endpoint. You can exclude the beginning point by
+waiting for the sequence number to be greater than 1.
If either operand of scalar ".." is a constant expression,
that operand is considered true if it is equal (C<==>) to the current
As a scalar operator:
if (101 .. 200) { print; } # print 2nd hundred lines, short for
- # if ($. == 101 .. $. == 200) { print; }
+ # if ($. == 101 .. $. == 200) { print; }
next LINE if (1 .. /^$/); # skip header lines, short for
# next LINE if ($. == 1 .. /^$/);
To get lower-case greek letters, use this instead:
- my @greek_small = map { chr } ( ord("\N{alpha}") .. ord("\N{omega}") );
+ my @greek_small = map { chr } ( ord("\N{alpha}") ..
+ ord("\N{omega}") );
Because each operand is evaluated in integer form, C<2.18 .. 3.14> will
return two elements in list context.
=head2 Yada Yada Operator
X<...> X<... operator> X<yada yada operator>
-The yada yada operator (noted C<...>) is a placeholder for code.
-It parses without error, but when executed it throws an exception
-with the text C<Unimplemented>:
-
- sub foo { ... }
- foo();
-
- Unimplemented at <file> line <line number>.
-
-It takes no argument.
+The yada yada operator (noted C<...>) is a placeholder for code. Perl
+parses it without error, but when you try to execute a yada yada, it
+throws an exception with the text C<Unimplemented>:
+
+ sub unimplemented { ... }
+
+ eval { unimplemented() };
+ if( $@ eq 'Unimplemented' ) {
+ print "I found the yada yada!\n";
+ }
+
+You can only use the yada yada to stand in for a complete statement.
+These examples of the yada yada work:
+
+ { ... }
+
+ sub foo { ... }
+
+ ...;
+
+ eval { ... };
+
+ sub foo {
+ my( $self ) = shift;
+
+ ...;
+ }
+
+ do { my $n; ...; print 'Hurrah!' };
+
+The yada yada cannot stand in for an expression that is part of a
+larger statement since the C<...> is also the three-dot version of the
+range operator (see L<Range Operators>). These examples of the yada
+yada are still syntax errors:
+
+ print ...;
+
+ open my($fh), '>', '/dev/passwd' or ...;
+
+ if( $condition && ... ) { print "Hello\n" };
+
+There are some cases where Perl can't immediately tell the difference
+between an expression and a statement. For instance, the syntax for a
+block and an anonymous hash reference constructor look the same unless
+there's something in the braces that give Perl a hint. The yada yada
+is a syntax error if Perl doesn't guess that the C<{ ... }> is a
+block. In that case, it doesn't think the C<...> is the yada yada
+because it's expecting an expression instead of a statement:
+
+ my @transformed = map { ... } @input; # syntax error
+
+You can use a C<;> inside your block to denote that the C<{ ... }> is
+a block and not a hash reference constructor. Now the yada yada works:
+
+ my @transformed = map {; ... } @input; # ; disambiguates
+
+ my @transformed = map { ...; } @input; # ; disambiguates
=head2 List Operators (Rightward)
X<operator, list, rightward> X<list operator>
The following escape sequences are available in constructs that interpolate
and in transliterations.
-X<\t> X<\n> X<\r> X<\f> X<\b> X<\a> X<\e> X<\x> X<\0> X<\c> X<\N>
-
- \t tab (HT, TAB)
- \n newline (NL)
- \r return (CR)
- \f form feed (FF)
- \b backspace (BS)
- \a alarm (bell) (BEL)
- \e escape (ESC)
- \033 octal char (example: ESC)
- \x1b hex char (example: ESC)
- \x{263a} wide hex char (example: SMILEY)
- \c[ control char (example: ESC)
- \N{name} named Unicode character
-
-The character following C<\c> is mapped to some other character by
-converting letters to upper case and then (on ASCII systems) by inverting
-the 7th bit (0x40). The most interesting range is from '@' to '_'
-(0x40 through 0x5F), resulting in a control character from 0x00
-through 0x1F. A '?' maps to the DEL character. On EBCDIC systems only
-'@', the letters, '[', '\', ']', '^', '_' and '?' will work, resulting
-in 0x00 through 0x1F and 0x7F.
-
-B<NOTE>: Unlike C and other languages, Perl has no \v escape sequence for
-the vertical tab (VT - ASCII 11), but you may use C<\ck> or C<\x0b>.
+X<\t> X<\n> X<\r> X<\f> X<\b> X<\a> X<\e> X<\x> X<\0> X<\c> X<\N> X<\N{}>
+X<\o{}>
+
+ Sequence Note Description
+ \t tab (HT, TAB)
+ \n newline (NL)
+ \r return (CR)
+ \f form feed (FF)
+ \b backspace (BS)
+ \a alarm (bell) (BEL)
+ \e escape (ESC)
+ \x{263a} [1,8] hex char (example: SMILEY)
+ \x1b [2,8] restricted range hex char (example: ESC)
+ \N{name} [3] named Unicode character or character sequence
+ \N{U+263D} [4,8] Unicode character (example: FIRST QUARTER MOON)
+ \c[ [5] control char (example: chr(27))
+ \o{23072} [6,8] octal char (example: SMILEY)
+ \033 [7,8] restricted range octal char (example: ESC)
-The following escape sequences are available in constructs that interpolate
+=over 4
+
+=item [1]
+
+The result is the character specified by the hexadecimal number between
+the braces. See L</[8]> below for details on which character.
+
+Only hexadecimal digits are valid between the braces. If an invalid
+character is encountered, a warning will be issued and the invalid
+character and all subsequent characters (valid or invalid) within the
+braces will be discarded.
+
+If there are no valid digits between the braces, the generated character is
+the NULL character (C<\x{00}>). However, an explicit empty brace (C<\x{}>)
+will not cause a warning.
+
+=item [2]
+
+The result is the character specified by the hexadecimal number in the range
+0x00 to 0xFF. See L</[8]> below for details on which character.
+
+Only hexadecimal digits are valid following C<\x>. When C<\x> is followed
+by fewer than two valid digits, any valid digits will be zero-padded. This
+means that C<\x7> will be interpreted as C<\x07> and C<\x> alone will be
+interpreted as C<\x00>. Except at the end of a string, having fewer than
+two valid digits will result in a warning. Note that while the warning
+says the illegal character is ignored, it is only ignored as part of the
+escape and will still be used as the subsequent character in the string.
+For example:
+
+ Original Result Warns?
+ "\x7" "\x07" no
+ "\x" "\x00" no
+ "\x7q" "\x07q" yes
+ "\xq" "\x00q" yes
+
+=item [3]
+
+The result is the Unicode character or character sequence given by I<name>.
+See L<charnames>.
+
+=item [4]
+
+C<\N{U+I<hexadecimal number>}> means the Unicode character whose Unicode code
+point is I<hexadecimal number>.
+
+=item [5]
+
+The character following C<\c> is mapped to some other character as shown in the
+table:
+
+ Sequence Value
+ \c@ chr(0)
+ \cA chr(1)
+ \ca chr(1)
+ \cB chr(2)
+ \cb chr(2)
+ ...
+ \cZ chr(26)
+ \cz chr(26)
+ \c[ chr(27)
+ \c] chr(29)
+ \c^ chr(30)
+ \c? chr(127)
+
+Also, C<\c\I<X>> yields C< chr(28) . "I<X>"> for any I<X>, but cannot come at the
+end of a string, because the backslash would be parsed as escaping the end
+quote.
+
+On ASCII platforms, the resulting characters from the list above are the
+complete set of ASCII controls. This isn't the case on EBCDIC platforms; see
+L<perlebcdic/OPERATOR DIFFERENCES> for the complete list of what these
+sequences mean on both ASCII and EBCDIC platforms.
+
+Use of any other character following the "c" besides those listed above is
+discouraged, and some are deprecated with the intention of removing
+those in Perl 5.16. What happens for any of these
+other characters currently though, is that the value is derived by inverting
+the 7th bit (0x40).
+
+To get platform independent controls, you can use C<\N{...}>.
+
+=item [6]
+
+The result is the character specified by the octal number between the braces.
+See L</[8]> below for details on which character.
+
+If a character that isn't an octal digit is encountered, a warning is raised,
+and the value is based on the octal digits before it, discarding it and all
+following characters up to the closing brace. It is a fatal error if there are
+no octal digits at all.
+
+=item [7]
+
+The result is the character specified by the three digit octal number in the
+range 000 to 777 (but best to not use above 077, see next paragraph). See
+L</[8]> below for details on which character.
+
+Some contexts allow 2 or even 1 digit, but any usage without exactly
+three digits, the first being a zero, may give unintended results. (For
+example, see L<perlrebackslash/Octal escapes>.) Starting in Perl 5.14, you may
+use C<\o{}> instead which avoids all these problems. Otherwise, it is best to
+use this construct only for ordinals C<\077> and below, remembering to pad to
+the left with zeros to make three digits. For larger ordinals, either use
+C<\o{}> , or convert to something else, such as to hex and use C<\x{}>
+instead.
+
+Having fewer than 3 digits may lead to a misleading warning message that says
+that what follows is ignored. For example, C<"\128"> in the ASCII character set
+is equivalent to the two characters C<"\n8">, but the warning C<Illegal octal
+digit '8' ignored> will be thrown. To avoid this warning, make sure to pad
+your octal number with C<0>s: C<"\0128">.
+
+=item [8]
+
+Several of the constructs above specify a character by a number. That number
+gives the character's position in the character set encoding (indexed from 0).
+This is called synonymously its ordinal, code position, or code point). Perl
+works on platforms that have a native encoding currently of either ASCII/Latin1
+or EBCDIC, each of which allow specification of 256 characters. In general, if
+the number is 255 (0xFF, 0377) or below, Perl interprets this in the platform's
+native encoding. If the number is 256 (0x100, 0400) or above, Perl interprets
+it as as a Unicode code point and the result is the corresponding Unicode
+character. For example C<\x{50}> and C<\o{120}> both are the number 80 in
+decimal, which is less than 256, so the number is interpreted in the native
+character set encoding. In ASCII the character in the 80th position (indexed
+from 0) is the letter "P", and in EBCDIC it is the ampersand symbol "&".
+C<\x{100}> and C<\o{400}> are both 256 in decimal, so the number is interpreted
+as a Unicode code point no matter what the native encoding is. The name of the
+character in the 100th position (indexed by 0) in Unicode is
+C<LATIN CAPITAL LETTER A WITH MACRON>.
+
+There are a couple of exceptions to the above rule. C<\N{U+I<hex number>}> is
+always interpreted as a Unicode code point, so that C<\N{U+0050}> is "P" even
+on EBCDIC platforms. And if L<C<S<use encoding>>|encoding> is in effect, the
+number is considered to be in that encoding, and is translated from that into
+the platform's native encoding if there is a corresponding native character;
+otherwise to Unicode.
+
+=back
+
+B<NOTE>: Unlike C and other languages, Perl has no C<\v> escape sequence for
+the vertical tab (VT - ASCII 11), but you may use C<\ck> or C<\x0b>. (C<\v>
+does have meaning in regular expression patterns in Perl, see L<perlre>.)
+
+The following escape sequences are available in constructs that interpolate,
but not in transliterations.
X<\l> X<\u> X<\L> X<\U> X<\E> X<\Q>
\u uppercase next char
\L lowercase till \E
\U uppercase till \E
- \E end case modification
\Q quote non-word characters till \E
+ \E end either case modification or quoted section
If C<use locale> is in effect, the case map used by C<\l>, C<\L>,
C<\u> and C<\U> is taken from the current locale. See L<perllocale>.
If Unicode (for example, C<\N{}> or wide hex characters of 0x100 or
beyond) is being used, the case map used by C<\l>, C<\L>, C<\u> and
-C<\U> is as defined by Unicode. For documentation of C<\N{name}>,
-see L<charnames>.
+C<\U> is as defined by Unicode.
All systems use the virtual C<"\n"> to represent a line terminator,
called a "newline". There is no such thing as an unvarying, physical
interpolated if the name is enclosed in braces C<@{*}>, but special
arrays C<@_>, C<@+>, and C<@-> are interpolated, even without braces.
-You cannot include a literal C<$> or C<@> within a C<\Q> sequence.
-An unescaped C<$> or C<@> interpolates the corresponding variable,
-while escaping will cause the literal string C<\$> to be inserted.
-You'll need to write something like C<m/\Quser\E\@\Qhost/>.
+For double-quoted strings, the quoting from C<\Q> is applied after
+interpolation and escapes are processed.
+
+ "abc\Qfoo\tbar$s\Exyz"
+
+is equivalent to
+
+ "abc" . quotemeta("foo\tbar$s") . "xyz"
+
+For the pattern of regex operators (C<qr//>, C<m//> and C<s///>),
+the quoting from C<\Q> is applied after interpolation is processed,
+but before escapes are processed. This allows the pattern to match
+literally (except for C<$> and C<@>). For example, the following matches:
+
+ '\s\t' =~ /\Q\s\t/
+
+Because C<$> or C<@> trigger interpolation, you'll need to use something
+like C</\Quser\E\@\Qhost/> to match them literally.
Patterns are subject to an additional level of interpretation as a
regular expression. This is done as a second pass, after variables are
optimizations, but none would be triggered in the above example if
we did not use qr() operator.)
-Options are:
+Options (specified by the following modifiers) are:
m Treat string as multiple lines.
s Treat string as single line. (Make . match a newline)
modifier has is not propagated, being restricted to those patterns
explicitly using it.
+Several other modifiers to control the character set semantics were
+added for 5.14 that, unlike the ones listed above, may not be used
+after the final pattern delimiter, but only following a C<"(?"> inside
+the regular expression. (It is planned in 5.16 to make them usable in
+the suffix position.) These are B<C<"a">>, B<C<"d">>, B<C<"l">>, and
+B<C<"u">>. They are documented in L<perlre/Extended Patterns>.
+
See L<perlre> for additional information on valid syntax for STRING, and
for a detailed look at the semantics of regular expressions.
Options are as described in C<qr//>; in addition, the following match
process modifiers are available:
- g Match globally, i.e., find all occurrences.
- c Do not reset search position on a failed match when /g is in effect.
+ g Match globally, i.e., find all occurrences.
+ c Do not reset search position on a failed match when /g is in effect.
If "/" is the delimiter then the initial C<m> is optional. With the C<m>
you can use any pair of non-whitespace characters
as delimiters. This is particularly useful for matching path names
that contain "/", to avoid LTS (leaning toothpick syndrome). If "?" is
-the delimiter, then the match-only-once rule of C<?PATTERN?> applies.
+the delimiter, then a match-only-once rule applies,
+described in C<m?PATTERN?> below.
If "'" is the delimiter, no interpolation is performed on the PATTERN.
When using a character valid in an identifier, whitespace is required
after the C<m>.
the pattern matched.
The C</g> modifier specifies global pattern matching--that is,
-matching as many times as possible within the string. How it behaves
-depends on the context. In list context, it returns a list of the
+matching as many times as possible within the string. How it behaves
+depends on the context. In list context, it returns a list of the
substrings matched by any capturing parentheses in the regular
-expression. If there are no parentheses, it returns a list of all
+expression. If there are no parentheses, it returns a list of all
the matched strings, as if there were parentheses around the whole
pattern.
In scalar context, each execution of C<m//g> finds the next match,
returning true if it matches, and false if there is no further match.
-The position after the last match can be read or set using the pos()
-function; see L<perlfunc/pos>. A failed match normally resets the
+The position after the last match can be read or set using the C<pos()>
+function; see L<perlfunc/pos>. A failed match normally resets the
search position to the beginning of the string, but you can avoid that
-by adding the C</c> modifier (e.g. C<m//gc>). Modifying the target
+by adding the C</c> modifier (e.g. C<m//gc>). Modifying the target
string also resets the search position.
=item \G assertion
You can intermix C<m//g> matches with C<m/\G.../g>, where C<\G> is a
-zero-width assertion that matches the exact position where the previous
-C<m//g>, if any, left off. Without the C</g> modifier, the C<\G> assertion
-still anchors at pos(), but the match is of course only attempted once.
-Using C<\G> without C</g> on a target string that has not previously had a
-C</g> match applied to it is the same as using the C<\A> assertion to match
-the beginning of the string. Note also that, currently, C<\G> is only
-properly supported when anchored at the very beginning of the pattern.
+zero-width assertion that matches the exact position where the
+previous C<m//g>, if any, left off. Without the C</g> modifier, the
+C<\G> assertion still anchors at C<pos()> as it was at the start of
+the operation (see L<perlfunc/pos>), but the match is of course only
+attempted once. Using C<\G> without C</g> on a target string that has
+not previously had a C</g> match applied to it is the same as using
+the C<\A> assertion to match the beginning of the string. Note also
+that, currently, C<\G> is only properly supported when anchored at the
+very beginning of the pattern.
Examples:
Notice that the final match matched C<q> instead of C<p>, which a match
without the C<\G> anchor would have done. Also note that the final match
-did not update C<pos>
-- C<pos> is only updated on a C</g> match. If the
+did not update C<pos>
. C<pos> is only updated on a C</g> match. If the
final match did indeed match C<p>, it's a good bet that you're running an
older (pre-5.6.0) Perl.
regexp tries to match where the previous one leaves off.
$_ = <<'EOL';
- $url = URI::URL->new( "http://example.com/" ); die if $url eq "xXx";
+ $url = URI::URL->new( "http://example.com/" ); die if $url eq "xXx";
EOL
LOOP:
{
- print(" digits"), redo LOOP if /\G\d+\b[,.;]?\s*/gc;
- print(" lowercase"), redo LOOP if /\G[a-z]+\b[,.;]?\s*/gc;
- print(" UPPERCASE"), redo LOOP if /\G[A-Z]+\b[,.;]?\s*/gc;
- print(" Capitalized"), redo LOOP if /\G[A-Z][a-z]+\b[,.;]?\s*/gc;
- print(" MiXeD"), redo LOOP if /\G[A-Za-z]+\b[,.;]?\s*/gc;
- print(" alphanumeric"), redo LOOP if /\G[A-Za-z0-9]+\b[,.;]?\s*/gc;
- print(" line-noise"), redo LOOP if /\G[^A-Za-z0-9]+/gc;
- print ". That's all!\n";
+ print(" digits"), redo LOOP if /\G\d+\b[,.;]?\s*/gc;
+ print(" lowercase"), redo LOOP if /\G[a-z]+\b[,.;]?\s*/gc;
+ print(" UPPERCASE"), redo LOOP if /\G[A-Z]+\b[,.;]?\s*/gc;
+ print(" Capitalized"), redo LOOP if /\G[A-Z][a-z]+\b[,.;]?\s*/gc;
+ print(" MiXeD"), redo LOOP if /\G[A-Za-z]+\b[,.;]?\s*/gc;
+ print(" alphanumeric"), redo LOOP if /\G[A-Za-z0-9]+\b[,.;]?\s*/gc;
+ print(" line-noise"), redo LOOP if /\G[^A-Za-z0-9]+/gc;
+ print ". That's all!\n";
}
Here is the output (split into several lines):
- line-noise lowercase line-noise lowercase UPPERCASE line-noise
- UPPERCASE line-noise lowercase line-noise lowercase line-noise
- lowercase lowercase line-noise lowercase lowercase line-noise
- MiXeD line-noise. That's all!
+ line-noise lowercase line-noise UPPERCASE line-noise UPPERCASE
+ line-noise lowercase line-noise lowercase line-noise lowercase
+ lowercase line-noise lowercase lowercase line-noise lowercase
+ lowercase line-noise MiXeD line-noise. That's all!
+
+=item m?PATTERN?
+X<?> X<operator, match-once>
=item ?PATTERN?
-X<?>
-This is just like the C</pattern/> search, except that it matches only
-once between calls to the reset() operator. This is a useful
+This is just like the C<m/PATTERN/> search, except that it matches
+only once between calls to the reset() operator. This is a useful
optimization when you want to see only the first occurrence of
-something in each file of a set of files, for instance. Only C<??>
+something in each file of a set of files, for instance. Only C<m??>
patterns local to the current package are reset.
while (<>) {
- if (?^$?) {
+ if (m?^$?) {
# blank line between header and body
}
} continue {
- reset if eof; # clear ?? status for next file
+ reset if eof; # clear m?? status for next file
}
-This usage is vaguely deprecated, which means it just might possibly
-be removed in some distant future version of Perl, perhaps somewhere
-around the year 2168.
+The match-once behaviour is controlled by the match delimiter being
+C<?>; with any other delimiter this is the normal C<m//> operator.
+
+For historical reasons, the leading C<m> in C<m?PATTERN?> is optional,
+but the resulting C<?PATTERN?> syntax is deprecated, will warn on
+usage and may be removed from a future stable release of Perl without
+further notice.
-=item s/PATTERN/REPLACEMENT/msixpogce
+=item s/PATTERN/REPLACEMENT/msixpogcer
X<substitute> X<substitution> X<replace> X<regexp, replace>
-X<regexp, substitute> X</m> X</s> X</i> X</x> X</p> X</o> X</g> X</c> X</e>
+X<regexp, substitute> X</m> X</s> X</i> X</x> X</p> X</o> X</g> X</c> X</e> X</r>
Searches a string for a pattern, and if found, replaces that pattern
with the replacement text and returns the number of substitutions
made. Otherwise it returns false (specifically, the empty string).
+If the C</r> (non-destructive) option is used then it will perform the
+substitution on a copy of the string and return the copy whether or not a
+substitution occurred. The original string will always remain unchanged in
+this case. The copy will always be a plain string, even if the input is an
+object or a tied variable.
+
If no string is specified via the C<=~> or C<!~> operator, the C<$_>
variable is searched and modified. (The string specified with C<=~> must
be scalar variable, an array element, a hash element, or an assignment
specific options:
e Evaluate the right side as an expression.
- ee Evaluate the right side as a string then eval the result
+ ee Evaluate the right side as a string then eval the result.
+ r Return substitution and leave the original string untouched.
Any non-whitespace delimiter may replace the slashes. Add space after
the C<s> when using a character allowed in identifiers. If single quotes
s/Login: $foo/Login: $bar/; # run-time pattern
($foo = $bar) =~ s/this/that/; # copy first, then change
+ ($foo = "$bar") =~ s/this/that/; # convert to string, copy, then change
+ $foo = $bar =~ s/this/that/r; # Same as above using /r
+ $foo = $bar =~ s/this/that/r
+ =~ s/that/the other/r; # Chained substitutes using /r
+ @foo = map { s/this/that/r } @bar # /r is very useful in maps
$count = ($paragraph =~ s/Mister\b/Mr./g); # get change-count
s/%(.)/$percent{$1} || $&/ge; # expr now, so /e
s/^=(\w+)/pod($1)/ge; # use function call
+ $_ = 'abc123xyz';
+ $a = s/abc/def/r; # $a is 'def123xyz' and
+ # $_ remains 'abc123xyz'.
+
# expand variables in $_, but dynamics only, using
# symbolic dereferencing
s/\$(\w+)/${$1}/g;
produces warnings if the STRING contains the "," or the "#" character.
-=item tr/SEARCHLIST/REPLACEMENTLIST/cds
+=item tr/SEARCHLIST/REPLACEMENTLIST/cdsr
X<tr> X<y> X<transliterate> X</c> X</d> X</s>
-=item y/SEARCHLIST/REPLACEMENTLIST/cds
+=item y/SEARCHLIST/REPLACEMENTLIST/cdsr
Transliterates all occurrences of the characters found in the search list
with the corresponding character in the replacement list. It returns
string specified with =~ must be a scalar variable, an array element, a
hash element, or an assignment to one of those, i.e., an lvalue.)
+If the C</r> (non-destructive) option is used then it will perform the
+replacement on a copy of the string and return the copy whether or not it
+was modified. The original string will always remain unchanged in
+this case. The copy will always be a plain string, even if the input is an
+object or a tied variable.
+
A character range may be specified with a hyphen, so C<tr/A-J/0-9/>
does the same replacement as C<tr/ACEGIBDFHJ/0246813579/>.
For B<sed> devotees, C<y> is provided as a synonym for C<tr>. If the
c Complement the SEARCHLIST.
d Delete found but unreplaced characters.
s Squash duplicate replaced characters.
+ r Return the modified string and leave the original string
+ untouched.
If the C</c> modifier is specified, the SEARCHLIST character set
is complemented. If the C</d> modifier is specified, any characters
tr/a-zA-Z//s; # bookkeeper -> bokeper
($HOST = $host) =~ tr/a-z/A-Z/;
+ $HOST = $host =~ tr/a-z/A-Z/r; # same thing
+
+ $HOST = $host =~ tr/a-z/A-Z/r # chained with s///
+ =~ s/:/ -p/r;
tr/a-zA-Z/ /cs; # change non-alphas to single space
+ @stripped = map tr/a-zA-Z/ /csr, @original;
+ # /r with map
+
tr [\200-\377]
[\000-\177]; # delete 8th bit
warning B<Can't find string terminator "END" anywhere before EOF...>.
Additionally, the quoting rules for the end of string identifier are not
-related to Perl's quoting rules -- C<q()>, C<qq()>, and the like are not
+related to Perl's quoting rules. C<q()>, C<qq()>, and the like are not
supported in place of C<''> and C<"">, and the only interpolation is for
backslashing the quoting character:
Processing of C<\Q>, C<\U>, C<\u>, C<\L>, C<\l>, C<\E>,
and interpolation happens (almost) as with C<qq//> constructs.
+Processing of C<\N{...}> is also done here, and compiled into an intermediate
+form for the regex compiler. (This is because, as mentioned below, the regex
+compilation may be done at execution time, and C<\N{...}> is a compile-time
+construct.)
+
However any other combinations of C<\> followed by a character
are not substituted but only skipped, in order to parse them
as regular expressions at the following step.
X<regexp, parse>
Previous steps were performed during the compilation of Perl code,
-but this one happens at run time--although it may be optimized to
+but this one happens at run time, although it may be optimized to
be calculated at compile time if appropriate. After preprocessing
described above, and possibly after evaluation if concatenation,
joining, casing translation, or metaquoting are involved, the
while (($_ = <STDIN>) ne '0') { ... }
while (<STDIN>) { last unless $_; ... }
-In other boolean contexts, I< C< E<lt>filehandleE<gt> > > without an
-explicit C<defined> test or comparison elicit a warning if the
+In other boolean contexts, C<< <filehandle> >> without an
+explicit C<defined> test or comparison elicits a warning if the
C<use warnings> pragma or the B<-w>
command-line switch (the C<$^W> variable) is in effect.
except that it isn't so cumbersome to say, and will actually work.
It really does shift the @ARGV array and put the current filename
into the $ARGV variable. It also uses filehandle I<ARGV>
-internally
--<> is just a synonym for <ARGV>, which
+internally
. <> is just a synonym for <ARGV>, which
is magical. (The pseudo code above doesn't work because it treats
<ARGV> as non-magical.)
use integer;
-you may tell the compiler that it's okay to use integer operations
-(if it feels like it) from here to the end of the enclosing BLOCK.
-An inner BLOCK may countermand this by saying
+you may tell the compiler to use integer operations
+(see L<integer> for a detailed explanation) from here to the end of
+the enclosing BLOCK. An inner BLOCK may countermand this by saying
no integer;
which lasts until the end of that BLOCK. Note that this doesn't
-mean everything is only an integer, merely that Perl may use integer
-operations if it is so inclined. For example, even under C<use
-integer>, if you take the C<sqrt(2)>, you'll still get C<1.4142135623731>
-or so.
+mean everything is an integer, merely that Perl will use integer
+operations for arithmetic, comparison, and bitwise operators. For
+example, even under C<use integer>, if you take the C<sqrt(2)>, you'll
+still get C<1.4142135623731> or so.
Used on numbers, the bitwise operators ("&", "|", "^", "~", "<<",
and ">>") always produce integral results. (But see also
printf "%.20g\n", 123456789123456789;
# produces 123456789123456784
-Testing for exact equality of floating-point equality or inequality is
-not a good idea. Here's a (relatively expensive) work-around to compare
+Testing for exact floating-point equality or inequality is not a
+good idea. Here's a (relatively expensive) work-around to compare
whether two floating-point numbers are equal to a particular number of
decimal places. See Knuth, volume II, for a more robust treatment of
this topic.
Here is a short, but incomplete summary:
- Math::Fraction big, unlimited fractions like 9973 / 12967
- Math::String treat string sequences like numbers
- Math::FixedPrecision calculate with a fixed precision
- Math::Currency for currency calculations
- Bit::Vector manipulate bit vectors fast (uses C)
- Math::BigIntFast Bit::Vector wrapper for big numbers
- Math::Pari provides access to the Pari C library
- Math::BigInteger uses an external C library
- Math::Cephes uses external Cephes C library (no big numbers)
- Math::Cephes::Fraction fractions via the Cephes library
- Math::GMP another one using an external C library
+ Math::Fraction big, unlimited fractions like 9973 / 12967
+ Math::String treat string sequences like numbers
+ Math::FixedPrecision calculate with a fixed precision
+ Math::Currency for currency calculations
+ Bit::Vector manipulate bit vectors fast (uses C)
+ Math::BigIntFast Bit::Vector wrapper for big numbers
+ Math::Pari provides access to the Pari C library
+ Math::BigInteger uses an external C library
+ Math::Cephes uses external Cephes C library (no big numbers)
+ Math::Cephes::Fraction fractions via the Cephes library
+ Math::GMP another one using an external C library
Choose wisely.
https://perl5.git.perl.org / perl5.git / blobdiff