Question

Could someone answer how many processes are created in each case for the commands below as I dont understand it :

The following three commands have roughly the same effect:

1. rm $(find . -type f -name '*.o')
2. find . -type f -name '*.o' | xargs rm
3. find . -type f -name '*.o' -exec rm {} \;

Answer 1

1. Exactly 2 processes – 1 for rm, the other for find.
2. 3 or more processes. 1 for find, another for xargs, and one or more rm. xargs will read standard input, and if it reads more lines than can be passed as parameters to a program (There is a maximum value named ARG_MAX).
3. Many processes, 1 for find and another one for each file ending in .o for rm.

In my opinion, option 2 is the best, because it handles the maximum parameter limit correctly and doesn’t spawn too many processes. However, I prefer to use it like this (with GNU find and xargs):

find . -type f -name '*.o' -print0 | xargs -0 rm

This terminates each filename with a \0 instead of a newline, since filenames in UNIX can legally contain newlines. This also handles spaces in filenames (much more common) correctly.