bash-verbosity-handling

Purpose:

Allows your script to accept varying levels of verbosity flags and give appropriate feedback via file descriptors.

Example usage:

sh-4.2$ ./verbosity-handling.sh 
Verbosity level set to: 2
This would not display 3
This would not display 4
This would not display 5
sh-4.2$ ./verbosity-handling.sh -v
Verbosity level set to: 3
This would display 3
This would not display 4
This would not display 5
This message is seen at verbosity level 3 and above.
sh-4.2$ ./verbosity-handling.sh -vv
Verbosity level set to: 4
This would display 3
This would display 4
This would not display 5
This message is seen at verbosity level 3 and above.
This message is seen at verbosity level 4 and above.
sh-4.2$

You could also use a command substitution inside of the descriptor redirection, to prepend a string to the debug output, such as this:

(( "$v" <= "$maxverbosity" )) && eval exec "$v> >( xargs -I{} printf '[Debug.%s] %s\n' "\$v" "{}" >&2 )"

or

(( "$v" <= "$maxverbosity" )) && eval exec "$v> >( sed 's/^/[Debug.$v] /' >&2 )"

The downside to these is that the external commands are slower to run than a builtin, and can result in the output getting out of order.