Redirect script output to log file OR terminal by request

Question

I'm writing a bash script that I want by default to output everything into a log file. However, I also want the ability to output it to the calling terminal by request (e.g. parameter) INSTEAD of the log file (so tee is out I believe). Does anyone know of a simple way to do this?

It would be nice if the parameter could be a custom log file OR a reference to a calling terminal.

I'm thinking along the lines of this: (pseudo-code)

#!/bin/bash

if [ ! $1 ]; then
    OUT="default.log"
else
    OUT=$1
fi

#then do this to every call in the script
commands [param] [param] >> ${OUT}

I guess more of what I am asking is, is there an easy way to reference the current terminal for output to? So I could do ./script.sh, ./script.sh custom.log or script.sh TERMINAL?

Answer 1

Using /dev/stdout as a filename would do what you want.

Answer 2

I might go with something like this:

#!/bin/bash

if [[ $1 != --stdout ]]; then
    exec >> "${1:-default.log}"
fi

commands [param] [param]

Result: If the user passes --stdout then output goes to stdout, otherwise it goes to a log file. The user can pass the log file name on the command-line, and if they don't specify one it defaults to default.log.

The exec part is nice because it redirects all future output from your script. It saves you from having to add >> ${OUT} to every single command.