Some say premature optimization is the root of all programming evils (but then they must not have ever used COBOL). Overly concise code is generally a bad idea in production, too. However, I think that without hurting clarity it's always better to remove code to fix a problem rather than moving it around. This can often be done simply for off-by-one errors.

foreach $line ( @fileData ) {
    $linenumber++;
    if ( $line =~ m/^1$/) {
        print "$linenumber\n";
    }
}
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Then there's the issue of idiomatic usage, which may or may not lead one to use $_, implicit matching against $_, or 'for' instead of 'foreach', depending one their views. This leads to code about as legible as the previous for many Perl coders, but I think it's fair to call it a matter of preference.

for ( @fileData ) {
    $linenumber++;
    if ( m/^1$/ ) {
        print "$linenumber\n";
    }
}
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Which shouldn't be confused at all with golf, which does hinder legibility somewhat.

$l++,/^1$/&&print$l.$/for@f;
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