How to get a file directory path from file path?

dirname and basename are the tools you're looking for for extracting path components:

$ export VAR='/home/pax/file.c'
$ echo "$(dirname "${VAR}")" ; echo "$(basename "${VAR}")"
/home/pax
file.c

They're not internal Bash commands but they're part of the POSIX standard - see dirname and basename. Hence, they're probably available on, or can be obtained for, most platforms that are capable of running bash.

$ export VAR=/home/me/mydir/file.c
$ export DIR=${VAR%/*}
$ echo "${DIR}"
/home/me/mydir

$ echo "${VAR##*/}"
file.c

To avoid dependency with basename and dirname

On a related note, if you only have the filename or relative path, dirname on its own won't help. For me, the answer ended up being readlink.

fname='txtfile'    
echo $(dirname "$fname")                # output: .
echo $(readlink -f "$fname")            # output: /home/me/work/txtfile

You can then combine the two to get just the directory.

echo $(dirname $(readlink -f "$fname")) # output: /home/me/work