Speeding file read and pattern search

hi,

i have very big files named outfile1 to outfile4 and i want to grep "test" in all files so i developed a code "program1.pl" its working fine but run time is very high (for 4 files its taking 10.7 sec ) if i run this for more (>100) big files its running for longtime, so i want to speed up .. can any one suggest me to improve speed for this ..

######### program1.pl ##########
#!/usr/bin/perl
open (INFILE, "> grepfile" );
foreach ($i = 1; $i< 5; $i++) {
$outfile = "outfile$i" ; # outfile1 .. outfile4
open ( OUTFILE, $outfile) ;
while (<OUTFILE> ) {
if ($_ =~ /test/ ) {
print "$_ \n";
print INFILE "line: $_ ";
}
}
close(OUTFILE);
}
close (INFILE);
#########################################

hi Zenthar,
thank you for your post,
actually the time is taking for opening the files. the time taken for grep in a file line by line pattern match or array pattern match is same ( means no much difference), i need a help to avoid the time consuming for file opening. even i used split command to split large files into small for processing and using fork function to process individually , even grepping paralleled for multiple files, their also i found splitting files consuming much time than processing in each big files. is their way to get referrence of line number in a file and that reference should be used for pattern match instead of opening a files ..