File Access

File input / output

• There's no prefix character for file handles.

Functions

open

open ( FILEHANDLE, FILENAME )

• Open a file for input and / or output
• Return values, 1 : success, 0 : failure

close

close ( FILEHANDLE )

• Close the file

Filename format

"FILE"     # Open FILE for input
"< FILE"   # Open FILE for input
"> FILE"   # Open FILE for output, creating it 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

Examples

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

if (open(DAT, "data.txt)) {   # Open the file for reading.
    $first_line=<DAT>;        # Read the first line.
    @raw_data=<DAT>;          # Read the rest of the file into an array.
    close(DAT);
}

if (open(DAT,">>data.txt")) {    # Open the file for appending.
    print DAT "More info\n";     # Append the string to the file.
    close(DAT);
}

if (open(DAT,">data.txt")) {    # Open the file for writing (overwriting).
    print DAT "$Some info\n";   # Write the string to file.
    close(DAT);
}

while (<DAT>) {  # Assigns each line in turn to $_
    print $_;    # Print the line to standard output.
}

File functions

unlink

unlink( FILENAME )

• Delete the file
  

File test operators

-r    readable
-x    executable
-e    exists
-d    directory
-t    is a tty
-T    text file                 

if (! -e "myfile") {  # If the file does not exist
    statements;
}