Programming Perl, 4th Edition

Specific Characters

As mentioned before, everything that’s not special in a pattern matches itself. That means an /a/ matches an “a”, an /=/ matches an “=”, and so on. Some characters, though, aren’t very easy to type in—and even if you manage that, they’ll just mess up your screen formatting. (If you’re lucky. Control characters are notorious for being out-of-control.) To fix that, regexes recognize the double-quotish character aliases listed in Table 5-10.

Table 5-10. Double-quotish character aliases

Escape	Meaning
\0	Null character (nul, null)
\a	Alarm (bel, alert)
\e	Escape (esc, escape)
\f	Form feed (ff, form feed)
\n	Newline (lf, line feed)
\r	Return (cr, carriage return)
\t	Tab (ht, horizontal tab)

Just as in double-quoted strings, patterns also honor the following five metasymbols:

\cX

A named ASCII control character, like \cC for Control-C, \cZ for Control-Z, \c[ for ESC, and \c? for DEL. The resulting ordinal must be 0–31 or 127.

\NNN

A character specified using its two- or three-digit octal code. The leading 0 is optional, except for values less than 010 (8 decimal) since (unlike in double-quoted strings) the single-digit versions are always considered to be references to strings captured by that numbered capture group within a pattern. Multiple digits are interpreted as the nth reference if you’ve captured at least n substrings earlier in the pattern (where n is considered as a decimal number). Otherwise, they are interpreted as a character specified in octal.

\x{HEXDIGITS}

A codepoint (character ...