Regular paths for bash do not work in termux app.
I tried:
/usr/bin/bash
and
/bin/bash
Also 'whereis' command gives the following output:
$ whereis bash bash:
/data/data/com.termux/files/usr/bin/bash
But this path also is not correct. So, I have to run every bash script with the word 'bash' before it. And cannot run bash scripts without it.