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 a
very old (pre-5.6.0) version of Perl.
A useful idiom for C-like scanners is C. You can
combine several regexps like this to process a string part-by-part,
doing different actions depending on which regexp matched. Each
regexp tries to match where the previous one leaves off.
$_ = <<'EOL';
$url = URI::URL->new( "http://example.com/" );
die if $url eq "xXx";
EOL
LOOP: {
print(" digits"), redo LOOP if /\G\d+\b[,.;]?\s*/gc;
print(" lowercase"), redo LOOP
if /\G\p{Ll}+\b[,.;]?\s*/gc;
print(" UPPERCASE"), redo LOOP
if /\G\p{Lu}+\b[,.;]?\s*/gc;
print(" Capitalized"), redo LOOP
if /\G\p{Lu}\p{Ll}+\b[,.;]?\s*/gc;
print(" MiXeD"), redo LOOP if /\G\pL+\b[,.;]?\s*/gc;
print(" alphanumeric"), redo LOOP
if /\G[\p{Alpha}\pN]+\b[,.;]?\s*/gc;
print(" line-noise"), redo LOOP if /\G\W+/gc;
print ". That's all!\n";
}
Here is the output (split into several lines):
line-noise lowercase line-noise UPPERCASE line-noise UPPERCASE
line-noise lowercase line-noise lowercase line-noise lowercase
lowercase line-noise lowercase lowercase line-noise lowercase
lowercase line-noise MiXeD line-noise. That's all!
=item C?msixpodualngc>
X X
This is just like the C/> search, except that it matches
only once between calls to the C operator. This is a useful
optimization when you want to see only the first occurrence of
something in each file of a set of files, for instance. Only C
patterns local to the current package are reset.
while (<>) {
if (m?^$?) {
# blank line between header and body
}
} continue {
reset if eof; # clear m?? status for next file
}
Another example switched the first "latin1" encoding it finds
to "utf8" in a pod file:
s//utf8/ if m? ^ =encoding \h+ \K latin1 ?x;
The match-once behavior is controlled by the match delimiter being
C; with any other delimiter this is the normal C operator.
In the past, the leading C in C?> was optional, but omitting it
would produce a deprecation warning. As of v5.22.0, omitting it produces a
syntax error. If you encounter this construct in older code, you can just add
C.
=item C/I/msixpodualngcer>
X X X X X
X X X X X X
X X X X X
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 (non-destructive) option is used then it runs the
substitution on a copy of the string and instead of returning the
number of substitutions, it returns the copy whether or not a
substitution occurred. The original string is never changed when
C is used. 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<$_>
variable is searched and modified. Unless the C option is used,
the string specified must be a scalar variable, an array element, a
hash element, or an assignment to one of those; that is, some sort of
scalar lvalue.
If the delimiter chosen is a single quote, no variable interpolation is
done on either the I or the I. Otherwise, if the
I contains a C<$> that looks like a variable rather than an
end-of-string test, the variable will be interpolated into the pattern
at run-time. If you want the pattern compiled only once the first time
the variable is interpolated, use the C option. If the pattern
evaluates to the empty string, the last successfully executed regular
expression is used instead. See L for further explanation on these.
Options are as with C with the addition of the following replacement
specific options:
e Evaluate the right side as an expression.
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 when using a character allowed in identifiers. If single quotes
are used, no interpretation is done on the replacement string (the C
modifier overrides this, however). Note that Perl treats backticks
as normal delimiters; the replacement text is not evaluated as a command.
If the I is delimited by bracketing quotes, the I has
its own pair of quotes, which may or may not be bracketing quotes, for example,
C or C<< s/bar/ >>. A C will cause the
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:
s/\bgreen\b/mauve/g; # don't change wintergreen
$path =~ s|/usr/bin|/usr/local/bin|;
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-cnt
$_ = 'abc123xyz';
s/\d+/$&*2/e; # yields 'abc246xyz'
s/\d+/sprintf("%5d",$&)/e; # yields 'abc 246xyz'
s/\w/$& x 2/eg; # yields 'aabbcc 224466xxyyzz'
s/%(.)/$percent{$1}/g; # change percent escapes; no /e
s/%(.)/$percent{$1} || $&/ge; # expr now, so /e
s/^=(\w+)/pod($1)/ge; # use function call
$_ = 'abc123xyz';
$x = s/abc/def/r; # $x is 'def123xyz' and
# $_ remains 'abc123xyz'.
# expand variables in $_, but dynamics only, using
# symbolic dereferencing
s/\$(\w+)/${$1}/g;
# Add one to the value of any numbers in the string
s/(\d+)/1 + $1/eg;
# Titlecase words in the last 30 characters only
substr($str, -30) =~ s/\b(\p{Alpha}+)\b/\u\L$1/g;
# 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.
$program =~ s {
/\* # Match the opening delimiter.
.*? # Match a minimal number of characters.
\*/ # Match the closing delimiter.
} []gsx;
s/^\s*(.*?)\s*$/$1/; # trim whitespace in $_,
# expensively
for ($variable) { # trim whitespace in $variable,
# cheap
s/^\s+//;
s/\s+$//;
}
s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields
Note the use of C<$> instead of C<\> in the last example. Unlike
B, we use the \> form only in the left hand side.
Anywhere else it's $>.
Occasionally, you can't use just a C to get all the changes
to occur that you might want. Here are two common cases:
# put commas in the right places in an integer
1 while s/(\d)(\d\d\d)(?!\d)/$1,$2/g;
# expand tabs to 8-column spacing
1 while s/\t+/' ' x (length($&)*8 - length($`)%8)/e;
=back
=head2 Quote-Like Operators
X
=over 4
=item C/>
X X X<'> X<''>
=item C<'I'>
A single-quoted, literal string. A backslash represents a backslash
unless followed by the delimiter or another backslash, in which case
the delimiter or backslash is interpolated.
$foo = q!I said, "You said, 'She said it.'"!;
$bar = q('This is it.');
$baz = '\n'; # a two-character string
=item C/>
X