Bash: Bad Substitution

Answer :

The default shell (/bin/sh) under Ubuntu points to dash, not bash.

me@pc:~$ readlink -f $(which sh) /bin/dash 

So if you chmod +x your_script_file.sh and then run it with ./your_script_file.sh, or if you run it with bash your_script_file.sh, it should work fine.

Running it with sh your_script_file.sh will not work because the hashbang line will be ignored and the script will be interpreted by dash, which does not support that string substitution syntax.

I had the same problem. Make sure your script didnt have

#!/bin/sh  

at the top of your script. Instead, you should add

#!/bin/bash 

For others that arrive here, this exact message will also appear when using the env variable syntax for commands, for example ${which sh} instead of the correct $(which sh)