shell scripting topic

cyperghost

My new project is a portable device with 4,3" screen and I2S soundmodule.
It has a foldable screen build in and if you open it you activate an trigger....
As it is still useable with HDMI I have two /boot/config.txt

One force activates HDMI and BCM sound
The other deactivaes HDMI, activates SDTV and uses I2S sound

So I coded a bash script that would exchange the the boot files in depence to the sensors.

I've build in a LED that show status. If SDTV config is already active and the foldable monitor is open then it will boot
If the SDTV config is active and the monitor is closed then LED will blink for a few seconds ... at this time you have the chance to open the LED screen. If not the config for HDMI will be exchanged and a reboot is forced.....

So here is my code
Bash is really a powerfull language, the functions call are super easy ;)

This one is dedicated to you... because it wasn't possible without your help

I hope you find some time to read the code and give opinion to the structure. Are the intenions setted right, are there some things in general to improve. This is not for puplic usage so if I set a file I know that I need it and I would not check .....

https://ghostbin.com/paste/kqqcq

meleu

@cyperghost dude, your coding style really improved! :-)

I did a quick look and have two or three comments about the coding (didn't focused on the logic). Will do soon. I'm on the phone now.

meleu

@cyperghost Looks like a ghost got your code! I was going to make my comments now and the code isn't there.

cyperghost

@meleu Sorry ;)
I setted wrong timer - this will be alive for 7 days now. I'm just busy :( But I hope to come back soon with a RetroAchivments link to you ;)
https://pastebin.com/LyA4dTwN

Neustart > reboot
Blinkschleife > loop for blinking
Befehle > commands
Wahl > selection
Abfrage Hallsensor > request hall sensors

Just to understand the comments a bit ;)

meleu

@cyperghost I've created a gist for your script: https://gist.github.com/meleu/0ea0b96ccafdbd0a432cb5a59a8c1835

We can comment there! ;-)

meleu

@cyperghost I've just noticed that I don't receive notifications on a gist comment...

I answered some of your questions there. :-)

cyperghost

@meleu I created a new GIST ;)

meleu

@cyperghost and I answered your questions there too. ;)

cyperghost

@meleu
Thank you for all your help.... I've something for you

inkey() { char="" ; stty -icanon min 0 time 1 ; char=`dd count=1 2>/dev/null` ; }

I hope you find that usefull ;)
source - Unix Linux Forums

meleu

@cyperghost Not sure what would be the purpose of that crazy function. I never programmed in Basic and don't know what INKEY$ does... :-)

bash lovers, I've found this doc and liked it: https://github.com/progrium/bashstyle

I didn't like every tip/recommendation there, but found it useful.

lilbud

This post is more of a forewarning

Don't use climate on the raspberry pi. This program is made to simplify several terminal commands to one or two words, sounds good in theory. But it auto runs and takes up resources. My Pi was sitting idle with climate running and it was at 80 Celsius (176 fahrenheit)

cyperghost

@meleu You can interrupt loops with that.
But I have to test if this is working with keypads also. If yes you can trigger events by keypad press and don't need enter key

In BASIC (afaik) you wrote it like this.... ucase is a function for uppercase characters so you dont use check for "q" and "Q".

Retro: Do loop was introduced in QBasic in 1991, former there were just if-then clauses and the goto/gosub command - really spooky

REM inkey function for basic
REM in anicient basic $ for charstrings is obligatory 
PRINT "Press Q to quit"
DO : LOOP UNTIL UCASE$(INKEY$)="Q"

!/bin/bash
# Demo do show function inkey
inkey() { char="" ; stty -icanon min 0 time 1 ; char=`dd count=1 2>/dev/null` ; }

# ---- main -----
echo "Press some keys and I will show you keybuffer after 3 seconds"
sleep 3 && inkey
echo "You wrote \"$char\""

meleu

@cyperghost be careful using this. It keeps your terminal busy and then you will be unable to input something to a simple read.

Check this script (I just added one single line at the end of your demo):

#!/bin/bash -
inkey() { char="" ; stty -icanon min 0 time 1 ; char=`dd count=1 2>/dev/null` ;}

# ---- main -----
echo "Press some keys and I will show you keybuffer after 3 seconds"
sleep 3 && inkey
echo "You wrote \"$char\""

read -p "Type something: " var

And here is the error I've found:

$ bash inkey.sh
Press some keys and I will show you keybuffer after 3 seconds
asdfgYou wrote "asdfg"
Type something: inkey.sh: linha 10: read: erro de leitura: 0: Resource temporarily unavailable

$ # and it messed my terminal even outside the script, look...

$ read -p "Type something: " var
Type something: -bash: read: erro de leitura: 0: Resource temporarily unavailable

"erro de leitura" (pt_BR) == "reading error" (en)

After this tests I used git to push some commits to one of my repos and when git asked my github username I've got that same error "Resource temporarily unavailable".

The good thing is that you can "fix" your terminal using the reset command (yes, just type reset and then <ENTER>).

I don't know the details of that stty command, but I think it's the responsible for the mess.

Summing up: use that inkey trick very carefully. Maybe performming a reset command after using inkey function is a good idea. :-)

Cheers!

cyperghost

@meleu Wow you are really master meleu

#!/bin/bash
# RESET is mandotary for releasing terminal from being busy
# inkey function demo
inkey() { char="" ; stty -icanon min 0 time 1 ; char=`dd count=1 2>/dev/null` ; }

# ---- main -----

echo "Press some keys and I will show you keybuffer after 3 seconds"
sleep 3
inkey && reset # <-- this is mandotary
echo "You wrote \"$char\""

read -p "Type something: " var
echo $var

I think this function is just a dirty trick. Thanks for looking deeper in. Just did a few simple tests with that.

meleu

@cyperghost talking about indentations in this thread to not messing that other.

@meleu ;) How about the indentations?

it really improved, I just would like to make one little note.

This snippet here

until [[ "${console[idx]}" == "$1" ]]
    do
       idx=$(( $idx + 1 ))
    done

Could be better indented this way:

until [[ "${console[idx]}" == "$1" ]]
do
    idx=$(( $idx + 1 ))
done

It's a more common practice.

I'm glad to see you improving your coding style! :-)

Cheers!

cyperghost

@meleu About your newest ES-termination code.
Is tty is setting the trigger to start the service? Don't get me wrong I thought tty is just the terminal like ssh ;) Can you please explain?

cyperghost

@meleu
Is there no annother approach?
systemd is very complicated?
Can we export a function call to shell that would end ES?
Can we use an alias ... as it can't be used from scripts - is there annother way?

meleu

@cyperghost There are as many approaches as creativity allows. I just tried to find a way to encompass as many use cases as possible. The explanation for how it works can be complex, but the steps to make it work is not.

Using an alias has its limitations, but it's an option.

cyperghost

@meleu Hello brother ;)
Yes I know it's maybe easy for me and you but take a look here
https://retropie.org.uk/forum/topic/12930/
I suggested the first solution (yours)
but it didn't work, so I used the "old" way.....

I bought now one of these mausberry devices to test ;)
It's really hard to test without the device.

AFAIK an alias can't be called within a script. So you may export the bash function with export -f func_call. But how this works? Do you have a clue?

meleu

@cyperghost said in shell scripting topic:

@meleu Hello brother ;)
Yes I know it's maybe easy for me and you but take a look here
https://retropie.org.uk/forum/topic/12930/
I suggested the first solution (yours)
but it didn't work, so I used the "old" way.....

I'll try to find what he made wrong. I think it was my fault: I didn't give really clear instructions for inexperienced Linux users.

I bought now one of these mausberry devices to test ;)
It's really hard to test without the device.

Oh yeah! Let's break that infinite loop!!

AFAIK an alias can't be called within a script.

I thought you were talking about creating an alias for shutdown command, making it call the killes.sh script before actually shutdown. But this approach has limitations.

So you may export the bash function with export -f func_call. But how this works? Do you have a clue?

When you export something in a shell (functions or variables) only the child shells will know the respective variable/function.

A good way would be to add this function and the export command to one of these files:

~/.profile
~/.bash_profile
~/.bashrc
/etc/profile
create a file at /etc/profile.d/ directory (btw, did you notice that you have a /etc/profile.d/10-retropie.sh on your RetroPie? :) )

But this approach also has its limitations...