The "while" loop works just like in 'C'.
More normal is the second example below.... Do something or process the lines that are "not blank", rather than find the first one.

Note that /^\s$/ means a regex that starts at the beginning to the end of the input and comprises all 5 white space characters
[ \t\f\r\n]

#!/usr/bin/perl -w
use strict;

my $firstNonBlankLine;
while ($firstNonBlankLine = <DATA>, $firstNonBlankLine !~ /\S/){}

print $firstNonBlankLine;

=prints
This first non-"blank" line
=cut

__DATA__



This first non-"blank" line

this is second non-blank line
[download]

Second Example:
Perhaps to print all the non-blank lines...

#!/usr/bin/perl -w
use strict;

while (<DATA>)
{
   print if !/^\s$/;
}

=prints
This first non-"blank" line
this is second non-blank line
=cut

__DATA__



This first non-"blank" line

this is second non-blank line
[download]