Sometimes, we do not just want to create or delete a file, we might need to rename one. Weirdly, Linux does not have anything that sounds like rename; however, the mv command (for move) does accomplish the functionality that we want. Similar to the cp command, it takes a source file and destination file as arguments, and looks like this:

reader@ubuntu:~$ ls -l
total 552
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 testdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 testfile
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:~$ mv testfile renamedtestfile
reader@ubuntu:~$ mv testdir/ renamedtestdir
reader@ubuntu:~$ ls -l
total 552
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 renamedtestdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 renamedtestfile
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:~$

As you can see, the mv command is really simple to use. It even works for directories, without needing a special option such as the -r we saw for cp and rm. It does, however, get a little more complex when we introduce wildcards, but don't worry about that for now. The commands we used in the preceding code are relative, but they work just as well fully qualified or mixed.

Sometimes, you'll want to move a file from one directory into another. If you think about it, this is actually a rename of the fully qualified file name! No data is being touched, but you just want to reach the file somewhere else. So, using mv umaskfile umaskdir/ will move the umaskfile into umaskdir/:

reader@ubuntu:~$ ls -l
total 16
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 renamedtestdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 renamedtestfile
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:~$ mv umaskfile umaskdir/
reader@ubuntu:~$ ls -l
total 16
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 renamedtestdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 renamedtestfile
drwxrwx--- 2 reader reader   4096 Aug 19 10:37 umaskdir
reader@ubuntu:~$ ls -l umaskdir/
total 0
-rw-rw---- 1 reader games 0 Aug  4 16:18 umaskfile
reader@ubuntu:~$

Finally, we have the ln command, which stands for linking. This is the Linux way of creating links between files, which are closest to the shortcuts that Windows uses. There are two types of links: symbolic links (also called soft links) and hard links. The difference is found deeper in the filesystem workings: a symbolic link refers to the filename (or directory name), whereas a hard link links to inode that stores the contents of the file or directory. For scripting, if you're using links, you're probably using symbolic links, so let's see those in action:

reader@ubuntu:~$ ls -l
total 552
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 renamedtestdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 renamedtestfile
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:~$ ln -s /var/log/auth.log 
reader@ubuntu:~$ ln -s /var/log/auth.log link-to-auth.log
reader@ubuntu:~$ ln -s /tmp/
reader@ubuntu:~$ ln -s /tmp/ link-to-tmp
reader@ubuntu:~$ ls -l
total 552
lrwxrwxrwx 1 reader reader     17 Aug 18 15:07 auth.log -> /var/log/auth.log
-rw-r--r-- 1 reader reader 550975 Aug 18 14:20 dpkg.log
lrwxrwxrwx 1 reader reader     17 Aug 18 15:08 link-to-auth.log -> /var/log/auth.log
lrwxrwxrwx 1 reader reader      5 Aug 18 15:08 link-to-tmp -> /tmp/
-rw-rw-r-- 1 reader reader     69 Jul 14 13:18 nanofile.txt
drwxrwxr-x 2 reader reader   4096 Aug  4 16:16 renamedtestdir
-rwxr-xr-- 1 reader reader      0 Aug  4 13:44 renamedtestfile
lrwxrwxrwx 1 reader reader      5 Aug 18 15:08 tmp -> /tmp/
drwxrwx--- 2 reader reader   4096 Aug  4 16:18 umaskdir
-rw-rw---- 1 reader games       0 Aug  4 16:18 umaskfile
reader@ubuntu:~$

We created two types of symbolic link using ln -s (which is short for --symbolic): to the /var/log/auth.log file first, and to the /tmp/ directory after. We are seeing two different ways of using ln -s: without a second argument, it creates the link with the same name as the thing we're linking to; otherwise, we can give our own name for the link as the second argument (as can be seen with the link-to-auth.log and link-to-tmp/ links). We can now read the contents of /var/log/auth.log by either interacting with /home/reader/auth.log or /home/reader/link-to-auth.log. If we want to navigate to /tmp/, we can now use either /home/reader/tmp/ or /home/reader/link-to-tmp/ in combination with cd. While this example isn't particularly useful in your day to day work (unless typing /var/log/auth.log instead of auth.log saves you tons of time), linking prevents duplicate copies of files while maintaining easy access.

Before continuing with the next part of this chapter, clean up the four links and the copied dpk.log file by using rm. If you're in doubt about how to do this, check out the man page for rm. A little tip: removing symbolic links is as simple as rm <name-of-link>!