>
> Got it so far.
>
> open CHECKFILE, "< file.in" or die qq(Cannot open file "file.in": $!);
> @filecontent = <INFILE>;
> foreach $line (@filecontent) {
> print " $line";
> }
> close (INFILE);
>
>
> The input file (list of files) looks something like this:
>
> P: 1 N: 11222
> P: 2 N: 22333
> P: 3 N: 33444
> P: 4 N: 44555
>
> How can I output just from the above code?
>
Have you tried using a match operator? Mastering the use of m// and
regexps in general is going to be critical path to enjoying Perl
programming.
First:
Read: perldoc perlop
Second:
if (my ($name) = $line =~ m/.*N: (\d+)$/) {
...do something with $name....
}
That's complex, so let's look at that bit by bit:
if (...something...) {
...do something with $name...
}
That should be self-evident. As to the ...something...
my ($name) = ...a match operation...
Remember, that when called in a list context, match operators will
return (quoting from perlop) "a list consiting of the subexpressions
matched by the parentheses in the pattern i.e. ($1, $2, $3 .. )"
So, by putting the $name inside a parentheses, it has been 'promoted'
from a scalar to a list-of-one, forcing the match operation to be
evaluated in a list context. As to the match operation ...
$line =~ m/.*N: (\d+)$/
That says:
search the string $line for any number of characters of any flavor
(could be zero), followed by a capital N, followed by a colon,
followed by one blank, followed by (and remember this part) one or
more digits, followed by the end-of-line.
So, that would match lines like:
My Mother Sucks Eggs N: 12345
P: 1 N: 11111
But would not match lines like:
P: 2 N: 22222c
The rain in spain falls mainly on the plain
So, if the match fails, it evaluates to undef, $name gets set to
undef, the if() block does not execute, no output is produced, nobody
gets soup.
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