# open a file for reading in the current directory
open(FILEHANDLE,"< some_file");

# open a file for reading using the full path (always a good idea)
open(FILEHANDLE,"< /home/my_user/some_file");

# open a file for writing
open(FILEHANDLE,"> /home/my_user/some_file");

# append to the end of a file
open(FILEHANDLE,">> /home/my_user/some_file");

# and it's always a good idea to check for failures ($! contains the error message)
open(FILEHANDLE,"< /home/my_user/some_file") || die "Can't read file: $!";

# be polite and close the file when you're done :)
close(FILEHANDLE);