Accepting name of changed file in fswatch with xargs in osx

In osx I am trying to detect when a new file is added to a folder, then execute a script to process that new file. Seems simple, right?

I am doing this:

fswatch  -0  ~/motion-detection | xargs -0 -n1 -I {} ./detectmotion.sh

which will call the shell script detectmotion.sh which consists of:

echo "File added: " $1

for now, at least. I just want to pass the filename of the changed file to detectmotion.sh

I get a blank for $1

Can anyone see what I am doing wrong here?

Thanks in advance!

Solution

It is expected to be empty because you are not passing the argument to the script detectmotion.sh which you got from xargs. It should have been

fswatch  -0  ~/motion-detection | xargs -0 -n1 -I {} ./detectmotion.sh "{}"

Remember that the -I {} flag in xargs represents a place-holder for the value pipe-lined to xargs. So in your attempt as part of the question, you are just storing the value in the place-holder({}) and not actually passing it to the script to make it useful.

So I modified the command so that you are actually passing the received value to the script which can now be printed when accessed as $1 inside the script.

Quoting from the man xargs page for -I

-I replace-str
     Replace  occurrences  of  replace-str  in the initial-arguments with names read from 
     standard input.  Also, unquoted blanks do not terminate input items; instead the 
     separator is the newline character.  Implies -x and -L 1.

In our case the replace-str being used as {}.