I tried a variation of your suggestion, with an added print debug line:
use strict;
use warnings;

open FILE1, '<', 'file1' or die ($!);

my %file1 = map { split '\|', $_ } <FILE1>;
## we now have A1=>'dog' in hash

close FILE1;

for(sort keys %file1){
  print "$_\n";
  print join('|',$_,$file1{$_}),'|',"\n";
}

[download]
and got:
Odd number of elements in hash assignment at combine2.pl line 6, <FILE1> line 3.
Use of uninitialized value in join or string at combine2.pl line 13.

||
A1
A1|dog|
A3
A3|bird|
cat
cat|
|

file1 is:
A1|dog|
A2|cat|
A3|bird|

In reply to Re^2: combining 2 files with a comon field by jjohhn
in thread combining 2 files with a comon field by jjohhn

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.