Building Parameters Programmatically

With Arrays

Created: 2021-02-13

Updated: 2021-04-29

Some programs, like ffmpeg, can take a lot of command line parameters.

I had written a bash script that I wanted to be able to call with different parameters.

As I found out, when we use a variable in bash like this:

FORMAT='-qscale:v 2 -f rtsp'```

When we call it, it is interpreted like this:

```bash
-qscale:v (2, -f, rtsp)```

```bash
-qscale:v is passed 2, -f, and rtsp```

Thanks to this post for explaining to use arrays.

So to get the correct behavior

PARAMS=(-qscale:v)
PARAMS+=(2)
PARAMS+=(-f)
PARAMS+=(rtsp)

Or Simply

PARAMS=(-qscale:v 2 -f rtsp)

And to 'unpack':

"${PARAMS[@]}"

Which I found very similar to Python equivalent of:

PARAMS=['-qscale:v', '2', '-f', 'rtsp']
subprocess.Popen(['ffmpeg', *PARAMS])