recursively trying to clear content of files

mnt_schred · 11-23-2013, 05:58 AM

In order to find shared photo's which I lost but others might have, I would like to sent people a zip with my photo's. I first wanted to send a list, but I realized that when I send them directory with subdirectories with emtpy files they can just copy their photo's over my files with 'overwrite none'. Then, after deleting the empty files, I can synchronize their photo's with mine.

I know I can empty files with cat /dev/null > filename
and I know I can list all .jpg files recuresively with .find -type '*.jpg'
but when I execute this command:

find . -name '*.jpg' -exec cat /dev/null > "{}" \;

nothing happens...
what am I doing wrong?

Madhu Desai · 11-23-2013, 08:09 AM

Interesting question... a quick google got these results:

Code:

find . -name '*.jpg' -exec /bin/bash -c "> '{}'" \;
find . -name '*.jpg' -exec dd if=/dev/null of="{}" \;

mnt_schred · 11-23-2013, 10:11 AM

I still don't get why the cat method wouldn't work though.. But this works!
I've used iname instead to also include files with capitals in the extension and added a few other filetypes; my final command is:

find . \( -iname \*.jpg -o -iname \*.mpg -o -iname \*.mov -o -iname \*.avi -o -iname \*.png \) -exec /bin/bash -c "> '{}'" \;

Thanks!

ntubski · 11-23-2013, 11:04 AM

Quote:

Originally Posted by mnt_schred

I still don't get why the cat method wouldn't work though..

Redirections (">") are handled by the shell, so when you say

Code:

find . -name '*.jpg' -exec cat /dev/null > "{}" \;

The shell does this

Code:

# execute find with the following arguments
find . -name *.jpg -exec cat /dev/null ;
# with output redirected to a file called {}

The arguments between -exec and ; are what find executes; obviously cat /dev/null produces nothing useful so you get an empty file called {}.

To handle the redirection the way you want, you to quote it to protect from the outer shell, and tell find to use a shell to interpret the quoted command:

Code:

find . -name '*.jpg' -exec /bin/bash -c "cat /dev/null > '{}'" \;

which means

Code:

# execute find with the following arguments
find . -name *.jpg -exec /bin/bash -c cat /dev/null > '{}' ;

Although, as you can see from mddesai's suggestion, cat and /dev/null aren't strictly needed.