Your question could use more details. I'll assume you're reading a list from a file, editing it, and writing it back to the same file.
open FILE, "myfile.txt" or die "Couldn't open for read!";
# stick all lines of file into an array of strings
@lines = <FILE>;
close FILE;
open FILE, ">myfile.txt" or die "Couldn't open for write!";
foreach $line (@lines)
{
# create a list of words in each line
@words = split ' ', $line;
# editing code goes here
if( $words[1] eq "posp" )
{
$words[0] = "edited";
}
# editing is done, now write the line to the file
print FILE $_." " foreach( @words );
print FILE "\n";
}
close FILE;
