open(MYFILE, ">file1");

Note: notice the '>' character before the filename, this means write mode

open(MYFILE, ">>file1");

Note: notice the '>>' character before the filename, this means append mode

if ( open(MYFILE, ">file1") ) {
    print "SUCCESS: the file was opened sucessfully";
}

open(MYFILE, "file1") || die("ERROR: unable to open file file1\n");
@input = <MYFILE>;
print (@input);

Note: we use the die function to abort if we cannot open the file

## Open the file in Read-Only mode
open(DATAFILE, "file1") || die("ERROR: unable to open file file1\n");

## The file contents will be destroyed
open(WRITEFILE, ">file2") || die("ERROR: unable to open file file2\n");

## The contents will not be destroyed, the data will be appended to the file
open(APPENDFILE, ">>file3") || die("ERROR: unable to open file file2\n");

$line = <DATAFILE>;
while ($line ne "") {
   print WRITEFILE ($line);
   print APPENDFILE ($line);
}

open(DATAFILE, "+>file1") || die("ERROR: unable to open file file1\n");

Note: this options allows you to overwrite portions of a file, it is mainly used with seek and tell which enable you to skip to the middle of a file

open(STDERR, ">c:/perl/error.log") || die("ERROR: unable to open error logfile\n");

open(STDOUT, ">c:/perl/program.log") || die("ERROR: unable to open program logfile\n");

if ( -e "file1") {
   open(MYFILE, "file1") || die("ERROR: unabl;e to open file file1");
} else {
   print "ERROR: file does not exists";
}

Note: check that the file exists

if ( (-e "file1") && (-w "file1") ) {
   open(MYFILE, "file1") || die("ERROR: unabl;e to open file file1");
} else {
   print "ERROR: file does not exists or is not writeable ";
}

Note: check that the file exists and is writeable

print "File size: " . (-s "c:/perl/error.log") . " bytes";

Note: obtain the size of a file

## Reading into an variable
while ($data = <>) {         ## when finished a null string will be passed terminating the loop
   print ($data);
}

## Reading into an array
@array = <>;                 ## you can now process the array as you wish

## The commandline would be as follows
perl_program file1 file2 file3

Note: the code above will read all 3 files that were passed as arguments.

## Perl command to run
perl_prog hello world

## The array @argv will contain the arguments passed
print("@argv");

## Access each argument individually
print ("First argument passed: $argv[0]");
print ("Second argument passed: $argv[1]");
print ("Third argument passed: $argv[2]");

open (MESAAGE, "| mail paul.valle@datadisk.co.uk");
print MESSAGE ("Hello how is the website coming along?");
close (MESSAGE);

Note: The call to open establishes a pipe to the command "mail paul.valle@datadisk.co.uk", the file variable MESSAGE is now associated with this pipe. The call to print add the line to the message to be sent. The call to close closes the pipe and the mail program can then send the mail message.

open (STDOUT, ">file1") || die("ERROR: open STDOUT failed");
open (STDERR, ">&SDOUT") || die ("ERROR: open STDERR failed");

$| = 1;                           ## turn buffering off for STDOUT
select (STDERR);                  ## change the default file to STDERR (normal default file is STDOUT)
$| = 1;                           ## turn buffer off for STDERR

print STDOUT ("Line One\n");
print STDERR ("Line Two\n");

close(STDOUT);
close(STDERR);

select (STDERR);                  ## This becomes the new default file

while ($line = <>) {
   print ($line);
   if (eof) {                       ## the eof returns a non-zero value, thus executing the if statement
      print ("------ END OF FILE CONTENTS -------\n");
   }
}

Note: you can use the eof() function as well, so you could do eof(MYFILE)

seek(MYFILE, 0, 0);           ## skip to beginning of file
seek(MYFILE, 0, 2);           ## skip to the end of the file

seek(MYFILE, 80, 1);          ## skip forward 80 bytes
seek(MYFILE, -80, 1);         ## skip backward 80 bytes

files_deleted = unlink ("file1", "file2");     ## delete the files file1 and file2, returns number of
                                               ## files acutally deleted

link("/u/pvalle/file1", "/u/pvalle/file2");    ## create a hard link

$timelist = gmtime(time());
print $timelist;

$timelist = localtime(time());
print $timelist;