bash script to test user input using read command

Question

I'm trying to do something really simple: Give myself the ability to choose what to run on boot. This is on a Raspberry Pi so sometimes it will be headless, sometimes it won't. I thought a simple approach would just be to run a little script on boot (don't even know if this will work - haven't gotten that far yet) that either lets me mash the keyboard and start up the GUI or just time out and start a python script. But yeah, I'm failing at this simple task. The if statement always evaluates to true no matter what I try, and I've tried many, many things. Here is the iteration I want to use...

If I let it time out, the return value of the read command should be greater than 128. If I press something the return value should be zero. So...

#!/bin/bash

# this gives the user the chance to startx or leave it alone and let camera.py run
# we will give the user 5 seconds to make a choice

/bin/echo "Hit any key to startx, otherwise I will start camera.py."

if [[ "$(read -t 5 -n 1)" -eq 0 ]]; then
    /bin/echo "You want to startx!"
else
    /bin/echo "You want to start the python script!"
fi

The result I get is that it always evaluates to true. What am I doing wrong?

John1024 · Accepted Answer · 2015-04-23 20:40:24Z

1

Replace:

if [[ "$(read -t 5 -n 1)" -eq 0 ]]; then

With:

if read -t 5 -n 1; then

If you type a character, read returns and exit code of zero (true). If read reaches end-of-file or it times out, it returns an exit code greater than zero (false). if responds to exit codes. There is no need for any test ([[) commands.

edited Apr 23, 2015 at 20:40

answered Apr 23, 2015 at 20:37

John1024

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1 Comment

noobiestofjavanoobs Over a year ago

Oh my goodness, thank you! I have to wait 8 minutes before I can hit the check mark, though.

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