File management

File management

Perl has very robust mechanisms for dealing with file input/output. The operators are similar to the forms of redirection you use on the command line, including > < >> | etc. The syntax is

 
	open(FILEHANDLE,FILENAME); 
	close(FILEHANDLE);

FILEHANDLEs aren't denoted a special character like $ @ %, and are not strings, so that's one reason to quote all your strings in a program.
the FILENAME is a string, special formats are below.
open returns 1 on success, 0 on failure

Conventions for opening files
"FILE"	open FILE for input also "<FILE"
"> FILE"	open FILE for output, creating if necessary
">> FILE"	open FILE for appending
"+> FILE"	open FILE with read/write access
"\| CMD"	open a pipe to CMD
"CMD \|"	open a pipe from CMD

Note the CMD can be an arbitrary bourne shell command, including its own pipes, redirection, etc.

Now that we have a filehandle, we need to read or write to it. The read operator is < >, as in

 
	# in a scalar context, read one line 
	$line = <FILEHANDLE>; 
	# in an array context, read the entire file (careful - this can take 
	#   lots of memory!) 
	@lines = <FILEHANDLE>;

To print to a FILEHANDLE, print takes an optional first argument which is the filehandle. How does it distinguish the first argument from the list of scalars to print? (warning - loss of beauty ahead) print takes a list as an argument (which as you'll remember is denoted by commas), so the first argument does not have a comma.

 
	print(FILEHANDLE "your","list","here");

Example

 
	# get ready to send the mail 
	if ( ! open(MAIL,"| $sendmail $recipient") ) { 
	    &error("Could not start mail program"); 
	}

The National Center for Supercomputing Applications
University of Illinois at Urbana-Champaign

johnsonb@ncsa.uiuc.edu

Last modified: June 19, 1997

Retrieved by Memoweb from http://www.ncsa.uiuc.edu/General/Training/PerlIntro/files.html at 08/02/99