The only prob I have now is, when applied to my real data a ">" sign is missing at the beginning ... and one is too much at the end.

The reason for this is the way the records are being split. The first record (and only the first) will have a leading ">", and all records except for the last will have a trailing ">". Now, if you happen to not print out the first record (because it doesn't match) the initial ">" will be missing from the output file. Similarly, if you happen to not print the last record, there will be a stray ">" from the previous record.

The proper way to handle those corner cases would be to always remove any leading or trailing ">"s, and always add a new one for output: 

...
# scan second file
while (<>) {
    s/^>//;  # remove leading  '>'
    s/>$//;  # remove trailing '>'

    print ">$_" if /^([\w\d]+)/ && $names{$1};
    #  add ^
}

[download]

(This way, you also no longer need to allow a leading ">" in the regex (the >? part). )

In reply to Re^3: awk 2 perl oneliner by almut
in thread awk 2 perl oneliner by space_agent

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.