One way is to loop over the indices of the array rather than the array items. 

for( my $i = 0; $i <= $#lines; $i++ ) {
    if ( $lines[$i] =~ s/^SY(?= )/CN/ ) {
        if ( defined $lines[$i+1] ) {
            $lines[$i+1] =~ s/^SY(?= )/  /;
        }
     }
}

[download]

Another way is to join all the lines into one large string and do replacements.

Still another way would be to use a flag variable to say when the previous line matched. 

my $previous_line_matched = 0;
foreach my $line ( @lines ) {
    if ( $previous_line_matched ) {
        $line =~ s/^SY(?= )/  /;
    }
    if ( $line =~ s/^SY(?= )/CN/ ) {
        $previous_line_matched = 1;
        next;
    }
    $previous_line_matched = 0;
}

[download]

In reply to Re: Modifying 'next' in foreach loop by kyle
in thread Modifying 'next' in foreach loop by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.