full contents of the file
ipc.writeSTR(0x3380, tab.."COM1_-"); -- display delected radio on green bar com1
As mentioned, if all that's in the file is that single line, it's a whole lot simpler to just write that out combined with the input from your command (which is what would happen anyway after reading the contents of the file).
E.G. if the "When I say" contents of your command are something like "set [com1;com2;com3;nav1;nav2] to [120..130].[075:20..199,5]", the action could look like
Write (overwrite), 'ipc.writeSTR(0x3380, tab.."COM1_{CMDSEGMENT:1} {CMDSEGMENT:3}.{CMDSEGMENT:5}-"); -- display selected radio on green bar com1' to file 'H:\fs...
The comment (I.E. everything after "--") won't be required for the functioning of that snippet, so you could choose to leave that off.
is there an alternative to "Quick Input"
An alternative that does what?
If you're just trying to check the contents of a variable, you can use the "Write a Value to the Event Log" action, which outputs text to the log on VoiceAttack's main window.