while( <> ) {
  chomp;
  if( tr/IMO//c ) {
    s/([^IMO]+)/[-->$1<--]/g;
    print "File: $ARGV, Line $.: $_\n";
  }
}

##</code><code>##

$ ./nonimo.pl filename1.txt filename2.txt

##</code><code>##

perl -lnE 'if(tr/IMO//c){s/([^IMO]+)/[-->$1<--]/g; say "$ARGV-$.: $_"}' file1.txt file2.txt fileXX.txt