Difference between \z and \Z and \a and \A in Perl

Question

Can you please tell me the difference between \\z and \\Z as well as \\a and \\A in Perl with a simple example ?

Answer 1

\z only matches the very end of the string.

\Z also matches the very end of the string, but if the string ends with a newline, then \Z also matches immediately before the newline.

So, for example, these five are true:

'foo' =~ m/foo\z/
'foo' =~ m/foo\Z/
"foo\n" =~ m/foo\Z/
"foo\n" =~ m/foo\n\z/
"foo\n" =~ m/foo\n\Z/

whereas this one is false:

"foo\n" =~ m/foo\z/

They both differ from $ in that they are not affected by the /m "multiline" flag, which allows $ to match at the end of any line.

\a denotes the alert (bell) character; it doesn't have any additional special meaning in a regex.

\A matches only at the start of a string. Like \z and \Z, and unlike ^, it's not affected by the /m "multiline" flag.

All of this is documented in perlre, the Perl regular expressions manual page: http://perldoc.perl.org/perlre.html.

Answer 2

The following indicates the positions at which the relevant regex patterns will match (␊ indicates a line feed):

\A                       \A is not affected by /m
^                        ^ without /m             ≡ \A
^/m  ^/m  ^/m            ^ with /m                ≡ \A|(?<=\n)
|    |    |
|    |    |
v    v    v
abc␊def␊ghi␊
   ^    ^    ^^
   |    |    ||___
   |    |    |    |
   $/m  $/m  $/m  $/m    $ with /m                ≡ (?=\n)|\z
             $    $      $ without /m             ≡ (?=\n\z)|\z
             \Z   \Z     \Z is not affected by /m ≡ (?=\n\z)|\z
                  \z     \z is not affected by /m

\a is equivalent to \x07, meaning it matches character 0x07 (BEL/BELL in ASCII and UNICODE).

This is documented in perlre.