Program Input and Output

Using Filehandles

• Once a filehandle has been opened, it is available for use.
• To write to a filehandle, use the print operator.
• print has an optional first argument to specify a desired file handle. If you leave off this first argument, it defaults to STDOUT.
• Example:
  

  # Open a log file for writing, overwrite each time
  $theFile = "/etc/passwd";
  unless ( open ( LOGFILE, ">$theFile" ) ) {
      die "I can't seem to open $theFile.\nError was $!\n";
  }
  
  print LOGFILE "Program GeeWiz up and running\n";
  

• To read from a filehandle, use the <FILEHANDLE> construct.
• Example:
  

  # Open the unix password file for reading
  $theFile = "/etc/passwd";
  unless ( open ( PASSWORD, "$theFile" ) ) {
      warn "I can't seem to open $theFile.  Continuing anyway.\n";
  }
  
  while ( defined ( $theLine = <PASSWORD> ) ) {
      print $theLine;
  }