Here is a string `"Hello, world!^["' that containing escape character. How can I remove escape character from this string? Let's get start it.
Note: raw escape char cannot see in web browser, so in this article I use two-bytes string `^[' as a single-byte escape char.
First way, put escape char literally in regexp.
my $str = "Hello, world!^[";
$str =~ s/^[//;
This is ok, but this way isn't copy-and-paste friendly.
Second way, use octal/hex char instead of raw escape sequence.
my $str = "Hello, world!^[";
$str =~ s/\x1B//; # \x1B is escape char
my $str = "Hello, world!^[";
$str =~ s/\033//; # \033 is escape char
These are also ok, but I think `\x1B' and `\033' are bit unreadable.
Third way, use POSIX character class `[[:print:]]'.
my $str = "Hello, world!^[";
$str =~ s/[^[:print:]]//;
Good. This is more readable than second way.
POSIX character classes looks like `[:name:]'. `[:' and `:]' are delimiter. `name' is self-descriptive. POSIX character classes are only available in bracketed character class. So valid regexp has continuous brackets looks like `[[:print:]]'.
POSIX character classes are just sets of characters, similar to a bracketed character class like `[aiueo]'. You can use POSIX character classes with any other parts of normal characters and meta characters.
/[[:alpha:]]/; # matches all of alphabet characters, same as [a-zA-Z].
/[cntrl[:cntrl:]]/; # matches control characters and five lower case alphabets `c', `n', `t', `r', `l'.
/[^[:print:]]/; # negation of [[:print:]], matches all non-printable characters.
For more details, see perlre and perlrecharclass.
Kensuke Kaneko (@kyanny)