Common file operations in perl part 1

Perl empowers the user with several useful functions for interacting with and manipulating files. In this atricle I'll talk about & demonstrate file copy, move, rename, delete operations. modify file permissions/ownerships & also about the stat function using which we can get some useful information about files.

I'll not take too much time explaining the syntax & usage of each of the functions since we can understand the usage from the function name itself but I'll talk a bit about the stat function.

So, the stat function is basically a thirteen element array & the array elements store information about different attributes of the file. Here is the list of elements:

0 Device number of file system
1 Inode number
2 File mode (type and permissions)
3 Number of (hard) links to the file
4 Numeric user ID of file.s owner
5 Numeric group ID of file.s owner
6 The device identifier (special files only)
7 File size, in bytes
8 Last access time since the epoch
9 Last modify time since the epoch
10 Inode change time (not creation time!) since the epoch
11 Preferred block size for file system I/O
12 Actual number of blocks allocated

To sum up the file manipulation operations, I've written the following perl script:

root@buntu:~# cat fileop.pl
#!/usr/bin/perl -w

use File::Copy;
use File::stat;

$file_name = "oldfile";
$copy = "oldfile_copy";
$second_copy = "oldfile_copy2";
$old_name = "oldfile";
$new_name = "newfile";
$new_path = "/tmp";

if ( -e $file_name )
 {
        ##copy file contents##

        copy ($file_name, $copy) || die "couldn't copy file $!";
        copy ($file_name, $second_copy) || die "couldn't copy file $!";
        copy ("$file_name", "${file_name}.bkp") || die "couldn't take a backup copy $!";

        ##copy file contents to the screen i.e STDOUT##

        copy ($file_name, \* STDOUT ) || die "couldn't print file to stdout  $!";

        ##move a file##

        move ("$old_name", "$new_path/") || die "couldn't move file $!";

        ##rename a file##

        rename ("$new_path/$old_name", "$new_path/$new_name") || die "couldn't rename file $!";

        ##list file & delete it##
        system ("ls /root/oldfile_copy2");
        unlink $second_copy ;

        ##change ownership & permissions##
        $uid = "1000" ;
        $gid = "1000" ;
        chown $uid, $gid, "$copy" ;
        chmod 0777, "$copy" ;

        system ("ls -l $copy") ;


        ##using stat function##

        $file_size = (stat ($copy))->size;
        $file_owner = (stat ($copy))->uid;

        print "file is owned by user with uid ", $file_owner, " size of the file is: ",  $file_size , " bytes \n"  ;

 }


The output of the execution of the script is as follows:

root@buntu:~# ./fileop.pl
this is a test file
/root/oldfile_copy2
-rwxrwxrwx 1 sa sa 20 Dec  6 21:52 oldfile_copy
file is owned by user with uid 1000 size of the file is: 20 bytes

This script performs the following tasks in order:

• copies a file
• prints the contents of the file to the screen
• moves & renames the file
• deletes a copy of the file
• changes permissions of a copy of the file
• uses stat function to get size of the file & the uid of the file owner & prints them