This operator quotes (and possibly compiles) its I<STRING> as a regular
expression. I<STRING> is interpolated the same way as I<PATTERN>
-in C<m/I<PATTERN>/>. If C<"'"> is used as the delimiter, no interpolation
-is done. Returns a Perl value which may be used instead of the
+in C<m/I<PATTERN>/>. If C<"'"> is used as the delimiter, no variable
+interpolation is done. Returns a Perl value which may be used instead of the
corresponding C</I<STRING>/msixpodualn> expression. The returned value is a
normalized version of the original pattern. It magically differs from
a string containing the same characters: C<ref(qr/x/)> returns "Regexp";
that contain C<"/">, to avoid LTS (leaning toothpick syndrome). If C<"?"> is
the delimiter, then a match-only-once rule applies,
described in C<m?I<PATTERN>?> below. If C<"'"> (single quote) is the delimiter,
-no interpolation is performed on the I<PATTERN>.
+no
variable interpolation is performed on the I<PATTERN>.
When using a delimiter character valid in an identifier, whitespace is required
after the C<m>.
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 interpolation is
+If the delimiter chosen is a single quote, no variable interpolation is
done on either the I<PATTERN> or the I<REPLACEMENT>. Otherwise, if the
I<PATTERN> contains a C<$> that looks like a variable rather than an
end-of-string test, the variable will be interpolated into the pattern
A character range may be specified with a hyphen, so C<tr/A-J/0-9/>
does the same replacement as C<tr/ACEGIBDFHJ/0246813579/>.
For B<sed> devotees, C<y> is provided as a synonym for C<tr>. If the
-I<SEARCHLIST> is delimited by bracketing quotes, the I<REPLACEMENTLIST> has
-its own pair of quotes, which may or may not be bracketing quotes;
-for example, C<tr[aeiouy][yuoiea]> or C<tr(+\-*/)/ABCD/>.
+I<SEARCHLIST> is delimited by bracketing quotes, the I<REPLACEMENTLIST>
+must have its own pair of quotes, which may or may not be bracketing
+quotes; for example, C<tr[aeiouy][yuoiea]> or C<tr(+\-*/)/ABCD/>.
Characters may be literals or any of the escape sequences accepted in
-double-quoted strings. But there is no interpolation, so C<"$"> and
-C<"@"> are treated as literals. A hyphen at the beginning or end, or
+double-quoted strings. But there is no variable interpolation, so C<"$">
+and C<"@"> are treated as literals. A hyphen at the beginning or end, or
preceded by a backslash is considered a literal. Escape sequence
details are in L<the table near the beginning of this section|/Quote and
Quote-like Operators>.
Note that C<tr> does B<not> do regular expression character classes such as
C<\d> or C<\pL>. The C<tr> operator is not equivalent to the C<L<tr(1)>>
-utility. If you want to map strings between lower/upper cases, see
-L<perlfunc/lc> and L<perlfunc/uc>, and in general consider using the C<s>
-operator if you need regular expressions. The C<\U>, C<\u>, C<\L>, and
-C<\l> string-interpolation escapes on the right side of a substitution
-operator will perform correct case-mappings, but C<tr[a-z][A-Z]> will not
-(except sometimes on legacy 7-bit data).
+utility. C<tr[a-z][A-Z]> will uppercase the 26 letters "a" through "z",
+but for case changing not confined to ASCII, use
+L<C<lc>|perlfunc/lc>, L<C<uc>|perlfunc/uc>,
+L<C<lcfirst>|perlfunc/lcfirst>, L<C<ucfirst>|perlfunc/ucfirst>
+(all documented in L<perlfunc>), or the
+L<substitution operator C<sE<sol>I<PATTERN>E<sol>I<REPLACEMENT>E<sol>>|/sE<sol>PATTERNE<sol>REPLACEMENTE<sol>msixpodualngcer>
+(with C<\U>, C<\u>, C<\L>, and C<\l> string-interpolation escapes in the
+I<REPLACEMENT> portion).
Most ranges are unportable between character sets, but certain ones
signal Perl to do special handling to make them portable. There are two
But, even for portable ranges, it is not generally obvious what is
included without having to look things up. A sound principle is to use
only ranges that begin from and end at either ASCII alphabetics of equal
-case (C<b-e>, C<b-E>), or digits (C<1-4>). Anything else is unclear
+case (C<b-e>, C<B-E>), or digits (C<1-4>). Anything else is unclear
(and unportable unless C<\N{...}> is used). If in doubt, spell out the
character sets in full.
the quoted material, and all lines following the current line down to
the terminating string are the value of the item.
+Prefixing the terminating string with a C<~> specifies that you
+want to use L</Indented Here-docs> (see below).
+
The terminating string may be either an identifier (a word), or some
quoted text. An unquoted identifier works like double quotes.
There may not be a space between the C<< << >> and the identifier,
=back
+=over 4
+
+=item Indented Here-docs
+
+The here-doc modifier C<~> allows you to indent your here-docs to make
+the code more readable:
+
+ if ($some_var) {
+ print <<~EOF;
+ This is a here-doc
+ EOF
+ }
+
+This will print...
+
+ This is a here-doc
+
+...with no leading whitespace.
+
+The delimiter is used to determine the B<exact> whitespace to
+remove from the beginning of each line. All lines B<must> have
+at least the same starting whitespace (except lines only
+containing a newline) or perl will croak. Tabs and spaces can
+be mixed, but are matched exactly. One tab will not be equal to
+8 spaces!
+
+Additional beginning whitespace (beyond what preceded the
+delimiter) will be preserved:
+
+ print <<~EOF;
+ This text is not indented
+ This text is indented with two spaces
+ This text is indented with two tabs
+ EOF
+
+Finally, the modifier may be used with all of the forms
+mentioned above:
+
+ <<~\EOF;
+ <<~'EOF'
+ <<~"EOF"
+ <<~`EOF`
+
+And whitespace may be used between the C<~> and quoted delimiters:
+
+ <<~ 'EOF'; # ... "EOF", `EOF`
+
+=back
+
It is possible to stack multiple here-docs in a row:
print <<"foo", <<"bar"; # you can stack them
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