How can I clear the contents of every file in a subdirectory without changing ownership / permissions?

Question

I can find the list of files using something like:

find /path/to/files -type f

And I can clear the contents of a single file with any of:

> filename

echo -n > filename

cat /dev/null > filename

You can do something like this with commands that don't involve output redirection:

find /path/to/files -type f -exec file '{}' \;

However this does not work:

find /path/to/files -type f -exec echo -n > '{}' \;

I can't seem to construct a command using find's -exec or | xargs to pipe the file list into one of these commands that will clear the files. How can I do this?

Solution 1

find /path/to/files -type f -exec /bin/sh -c "> '{}'" ';' should do what you want; see find(1) for details on how exec works in detail, but this invocation runs the command once, putting the filename where {} is.

You can also tell xargs to only pass a single filename to the command, or use find /path -type f | while read file; do echo -n > "$file"; done to do that at the shell level.

Solution 2

Just for fun, here's another option:

find /path/to/files -type f -exec dd if=/dev/null of={} \;

Comments

[Daniel Pittman]

Sorry, I should have noticed that wouldn't work - I didn't think about it, just copied it from your example. The update shows how to fix that; invoking a single shell command. Using the "| while read file; do" version would also work smoothly.

[Dave Forgac]

Nice! I was trying to think of a way to avoid the redirection.

[Eduardo B.]

This one works! Straightforward approach.

[Hashim Aziz]

This was perfect for me.

[Hashim Aziz]

Out of interest, what is of={} ` doing here? I understand of` is dd's output file, but the braces and the following backslash are what are throwing me off.

[Gordon Davisson]

@Hashim The {} is part of the syntax for find's -exec primary; it basically means "put filepath/name here", so you get of=path/to/file. The backslash makes the shell pass the following ; to find as an argument, rather than treating it as a delimiter ending the command. And the ; is, again, part of the -exec syntax that indicates the end of the command to execute. Compare with @DanielPittman's answer, which uses {} the same way (but in a different context), and puts ; in single-quotes (which has the same effect as escaping it).