How does /bin/bash -c differ from executing a command directly?

Question

I'm curious why the commmand:

for f in `/bin/ls /mydir | sort | tail -n 10`; do echo $f; done;

Outputs the last ten files in /mydir, but

/bin/bash -c "for f in `/bin/ls /mydir | sort | tail -n 10`; do echo $f; done;"

Outputs "syntax error near unexpected token '[file in /mydir]'"

Answer 1

You are using double-quotes, so the parent shell is interpolating backticks and variables before passing the argument to /bin/bash.

Thus, your /bin/bash is receiving the following arguments:

-c "for f in x
y
z
...
; do echo ; done;"

which is a syntax error.

To avoid this, use single quotes to pass your argument:

/bin/bash -c 'for f in `/bin/ls /mydir | sort | tail -n 10`; do echo $f; done;'