Intro To 'cp' Command In Linux

2023-04-22 - By Robert Elder

I use the 'cp' command to copy files on my computer:

cp cat.jpg cat_copy1.jpg

I also use it to make copies of entire directories. If I try to make a copy of the directory 'all-photos' like this:

cp all-photos photos-backup-copy

I'll see an error message like this:

cp: -r not specified; omitting directory 'all-photos'

To copy directories, I need to use the '-r' flag:

cp -r all-photos photos-backup-copy

I can also use the '-p' flag to preserve permission and ownership information on the copied file:

ls -l

If we start with this file:

-rw-rwxr-- 1 mike   mike   1048576 Apr 23 21:35 dog.jpg

and run these two copy commands:

cp dog.jpg dog_copy1.jpg
sudo cp -p dog.jpg dog_copy2.jpg

and then re-run the ls command:

ls -l

the output is now this:

-rw-rwxr-- 1 robert robert 1048576 Apr 23 21:38 dog_copy1.jpg
-rw-rwxr-- 1 mike   mike   1048576 Apr 23 21:35 dog_copy2.jpg
-rw-rwxr-- 1 mike   mike   1048576 Apr 23 21:35 dog.jpg

this illustrates the difference when using the '-p' flag.

If you're not careful, you can overwrite an existing file when making a copy:

ls -l

total 1024
-rw-rwxr-- 1 robert robert 1048576 Apr 23 21:38 dog_copy1.jpg
-rw-rw-r-- 1 robert robert       0 Apr 23 21:45 empty.txt

cp empty.txt dog_copy1.jpg

ls -l

total 0
-rw-rwxr-- 1 robert robert 0 Apr 23 21:46 dog_copy1.jpg
-rw-rw-r-- 1 robert robert 0 Apr 23 21:45 empty.txt

As you can see above, the 'dog_copy1.jpg' file has been overwritten with the 'empty.txt' and the original data has been lost.

That's why I use the '-n' flag to prevent this from happening:

ls -l

total 1024
-rw-rwxr-- 1 robert robert 1048576 Apr 23 21:38 dog_copy1.jpg
-rw-rw-r-- 1 robert robert       0 Apr 23 21:45 empty.txt

cp -n empty.txt dog_copy1.jpg

ls -l

total 1024
-rw-rwxr-- 1 robert robert 1048576 Apr 23 21:47 dog_copy1.jpg
-rw-rw-r-- 1 robert robert       0 Apr 23 21:45 empty.txt

And that's why the 'cp' command is my favourite Linux command.

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