Re: tonight's meeting

[Steven Pritchard <steve@silug.org>]

Jay Link said:
> Since you might not make it tonight, how about giving us all another
> Perl regex lesson?  :-)

Sure, why not.

> The following construction takes the second word in a string from
> <STDIN> and makes it the entirety of the string. It works, but I only half
> understand it.
> 
> $_ =~ s/^([^ ]+) +([^ ]+).*/$2/;

OK, first of all, "$_ =~" is not necessary.  s/// operates on $_ by
default.

Next, here's how I'd probably write that:

    s/^(\S+)\s+(\S+).*$/$2/;

Since "[^ ]" means "not a space", in perl you may as well use \S,
which means "not a whitespace character", since that's probably what
you really mean.  Ditto for "\s" instead of " " ("whitespace
character" instead of a literal space).  So, here's what the left-hand
side breaks down to:

    ^      anchor at the beginning of the line/string
    (\S+)  one or more ("+") non-whitespace characters("\S"), assign
           it to $1 since it is the first grouped expression (in
           parentheses)
    \s+    one or more whitespace characters ("\s")
    (\S+)  assign the next series of one or more non-whitespace
           characters to $2
    .*     everything else (literally any number ("*") of any
           character ("."))
    $      anchor at the end of the line/string

Of course, the right-hand side replaces all of that with whatever is
in $2.

Steve
-- 
steve@silug.org           | Southern Illinois Linux Users Group
(618)398-7320             | See web site for meeting details.
Steven Pritchard          | http://www.silug.org/
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