Programming

$o_dups{$1} = 1 if /^\w+\t.{19}\t([^,]+),/;

$o_dups{$1} = 1 if /^\w+\t.{19}\t([^,]+),/;

$o_dups{$1}=1 # set the value in the o_dups hash for the match capture ($1) to true 
 if /^\w+\t.{19}\t([^,]+),/;#if the regex matches

/^ # beinning of line
\w+# one or more "word" characters, (ie. alphanumeric + "_")
 \t # a litteral tab
.{19} # any 19 characters
\t # a literal tab again
([^,]+) # A series of non "," chars in brackets so capture this as the first capture ($1 above)
,#followed by a comma
/ #End match