File Handles
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What are They Handles To?
These handles can be associated with files, pipes or socket
connections (depending on how your version of Perl was built). The
most common use, is a handle to a file.
Built-in File Handles
There are three built-in file handles that you get for free:
STDIN, STDOUT and STDERR. These
are the familiar stdin, stdout and
stderr that C programmers have come to know and love.
Creating File Handles
You can "create" a file handle with the open()
function call, as in:
<![CDATA[
# open $log for reading
open (LOG_FILE, $log) or die "Can't open $log: $!\n";
# the same as above
open (LOG_FILE, "<$log") or die "Can't open $log: $!\n";
# create file and write to it
open (LOG_FILE, ">$log") or die "Can't open $log: $!\n";
# create file and write and read
open (LOG_FILE, "+>$log") or die "Can't open $log: $!\n";
# append to existing file
open (LOG_FILE, ">>$log") or die "Can't open $log: $!\n";
open (LOG_FILE, "| output-pipe-command") or
die "Can't open pipe: $!\n"; # set up output pipe filter
open (LOG_FILE, "input-pipe-command |") or
die "Can't open pipe: $!\n"; # set up input pipe filter
]]>
The convention is to use all uppercase characters for file handles.
Using File Handles
Some examples of using file handles include:
<![CDATA[
# Read a line from the keyboard (or stdin).
$answer = <STDIN>;
# Write a line to a file on disk.
print LOF_FILE ("Fatal error in I/O sub-system. " .
"System going down\n");
# Read in all the contents of a file into an array.
@contents = <RIGHTEOUS_DATA>; # array context
]]>
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Last Modified: $Date: 1997/05/02 07:17:38 $