shell scripting topic

meleu

Answering your questions on this nerdy thread.

@cyperghost said in Mausberry Shutdown Script Doesn't Save Metadata:

@meleu
About using variables? You see I'm avoiding these and use just a bunch of them...
Is there any difference? Speed up? Memory usage?

I know it's better for clear code reading.... but is that effcient?

It was just for clear code reading. Each variable have a meaningful name. In such a small script the impact on performance is null. But to be honest, using emupid didn't cause any impact on code reading too. :)

About avoiding variables and using the same command two or more times, that would cause impact on performance.

Example:

[[ "$(pgrep -P $emupid)" ]] && kill $(pgrep -P $emupid)

Using a variable for $(pgrep -P $emupid) is preferable in this case.

We (programmers) should always think where (and when) our code is supposed to be executed when deciding about "Memory Usage vs. Processing Usage". Some questions we should keep in mind when coding:

The system has a good amount of RAM?
The system has a good CPU power?
The system has usually several users/processes sharing resources?
How often will my code run?
How long will my code remain running?

There are more questions, obviously.

By the way, those last 2 question are the ones that bother me so much about that infinite loop! We are looping to check a file content every single second just to execute a command to SHUT DOWN THE WHOLE SYSTEM! In my head the thought is: "this script is wasting 99.99999% of its CPU time slice!". Specially because there are ways to make a script do nothing (just wait) while that file doesn't change!

But... Well... I don't have that f!@#%ing mausberry switch, so there's no need for me to worry about it. Those guys who have it are happy with our current solution... Let's play some games! :D

This subject would be a good nerdy chat while drinking some Caipirinhas when you come to Rio.

Sano

Hi guys, sorry, wasn't here for a while.
I've read @meleu last post and I just checked "things", as I'm also not fond of the infinite loop. That said, I don't use mausberry or gpio either.

Did you take a look at the gpio util from wiringpi ?
http://wiringpi.com/the-gpio-utility/

I found this option in the doc, that may help (if I understood your need) :

gpio wfi <pin> rising/falling/both

This causes GPIO to perform a non-busy wait on a single GPIO pin until it changes state to that indicated.

cyperghost

@meleu I have to say thank you for your detailed explanation. I'm currently on holidays ... so I'm a bit quieter in this forum for couple of days. I think during these days a few things will change to ES ...
But I take my portable Pi to the airport with a copy of Terranigma on it (I deeply hope that I will save humankind during may holiday)...

We are looping to check a file content every single second just to execute a command to SHUT DOWN THE WHOLE SYSTEM! In my head the thought is: "this script is wasting 99.99999% of its CPU time slice!".

I understand you... about the inotify thing...
But without the real hardware it's a bit a pain ... but it's solvable imho
Maybe a chmod to the exported GPIO files will help.

  echo "$GPIOpin1" > /sys/class/gpio/export
  echo "in" >/sys/class/gpio/$GPIOpin1/direction
  chmod 660 /sys/class/gpio/$GPIOpin1/direction
  chmod 660 /sys/class/gpio/$GPIOpin1/value

This subject would be a good nerdy chat while drinking some Caipirinhas when you come to Rio.

Oh yes :) It's all about games ... As I told you it's more likely to expand to the eastern hemisphere but never say never and if I'm on buisness journey I'll surly come back to your offer.

@Sano
Welcome to this thread

Yes I told also to use gpio-control. wPi is also a solution but I think this approach is an overkill to just monitor ONE Gpio. I use wPi in my work as it got's powerfull IRQ functions but you have to load a whole C programm to just monitor ONE GPIO and I think that's not attentend to be called "effective".

Also think about you have to compile the thing and I think this approach isn't user friendly anymore. So way meleu want it to do is really nice. It comes very far to RT processing!

cyperghost

@meleu

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?