Re^2: About a piece of code

[Marshall]

This is skipping lines which only have a new line char at the start. m/^\s*$/ is a better way of saying a line with only white space characters because it allows any number of non-printing whitespace characters on the line. Whitespace is \n\f\s\f\r Update: oof..goof should be \n\f\s\t\r order doesn't matter, but there are 5 of these white space critters and I goofed! Ooops!

m/^\n/ and next; ... }
This is sort of a "cheater" way to execute the "next" if the match is true. Sometimes this is a good idea, sometimes not. I would probably code it like this:

next if m/^\s*$/;     #skip/re-prompt for blank lines
#or
if (m/^\s*$/)  #very unlikely that I would write this
{              #but, it means the same as above
   next;
}
I would not write the below. This is obfuscated bad code.
Because it obscures the "if" nature of the statement.
m/^\s*$/ and next;

[jwkrahn]

Whitespace is \n\f\s\f\r Update: oof..goof should be \n\f\s\t\r order doesn't matter,

\s is not a whitespace character.   In a regular expression it is a character class that includes the characters [ \t\n\r\f] and in a double quoted string it is the character s.

[Marshall]

\s is the single space ' ' character. In your set [ \t\n\r\f] that thing right before the \t is \s.

Oooh I see now... in a character set [\s\t\f\r\n], \s means a single space.
in a regex \s means all of the chars in this set: [\s\t\f\r\n]. Yep, confusing!!
\s has a context dependent meaning. Such as it is.

[jwkrahn]

\s is not a single character in a regular expression, it is the character class [ \t\n\r\f].   See perlre.

$ perl -le'
 use Data::Dumper;
 $Data::Dumper::Useqq = 1;
 print Dumper grep /\s/, map chr, 0 .. 255;
'
$VAR1 = "\t";
$VAR2 = "\n";
$VAR3 = "\f";
$VAR4 = "\r";
$VAR5 = " ";

In a double quoted string it is just the character "s".

$ perl -le'
 use Data::Dumper;
 $Data::Dumper::Useqq = 1;
 print Dumper "\s";
'
$VAR1 = "s";

[JadeNB]

I think that, since the common regex wisdom involves replacing a literal space in an /x-modified regex with \s, it's easy to think of \s as a replacement for a literal space—but, if you actually want a literal space (rather than just a single whitespace character) in such a regex, but outside a character class, then what you want is '\' (i.e., an escaped space).