Regular expression for file path which doesn't allow parent directories

Question

I'm looking to write a regex for a file path that must start with some prefix. In this case it should start with '/tank/home/'. I also want to make sure that it contains no '/..' -- no jumping up to parent directories.

I spent a while fiddling around without coming up with anything quite right. I settled on using two regexes, the first which must match and the second which must not match:

'^/tank/home/'

'/\.\.(/.*)?$'

Does this do what I think it does? Is there an easier way?

This is in a bash script, for what it's worth.

Answer 1

You could use a negative lookahead to make sure that there aren't any /.. in the string:

^(?!.*/\.\..*)/tank/home.*$

Answer 2

You could use negative lookbehind too:

\/tank\/home\/([^\/]|?(<!\/..)\/)+$

Answer 3

You can expand Dav's regex to include an extra trailing slash:

^(?!.*/\.\./.*)/tank/home.*$

But... a better option might be to make sure that the result of the path is something that starts under /tank/home:

FILEPATH=$(readlink -f $YOURFILE)
[[ $FILEPATH =~ ^/tank/home/ ]] && echo "starts with /tank/home/"

Answer 4

'^/tank/home(?!.*/\.\.(/|$))/'

matches /tank/home/foo..bar but not /tank/home/.. or /tank/home/foo/../bar