shell scripting topic

[meleu]

@cyperghost Just to share some bash coding knowledge, I would like to make some comments about your bash coding philosophy :)

• the bash scripting language is an interpreted programming language
• if you google about "compiled vs intepreted language" and you realize that interpreted languaged tends to be slower.
• type man bash on your terminal, go the end of the bash man page and look at the first sentence in the BUGS section. ;-)

Why is @meleu trying to convince me that bash is slow if he loves bash?

Well, I love bash because it is widely used. If it wasn't for that I would have migrated to zsh (which is even more powerfull), but let's not go deep into this nerdy stuff...

I'm talking all those things because of your very good practice of checking if everything is really fine before running a command. In other languages, if you don't do these checkings, the program may crash. But when coding bash scripts (or any other shell language) it's a better yet practice to take advantage of every chance you have to optimize things.

I'm talking specifically for this part:

if [[ -e "/dev/shm/runcommand.info" ]]; then
    emupid="$(sed -n 4p /dev/shm/runcommand.info | tr -d '\\"' | tr '^$[]*.()|+?{}' '.')"
    emupid="$(pgrep -f "$emupid")" 
fi
 
if [ "$emupid" ]; then
    kill $emupid && sleep 9
fi
 

You're making bash check if the runcommand.info exists, but sed already does that.
You're getting the emulator's PID with pgrep, but pkill won't kill anything if there isn't a process matching the pattern.

That's why I would change all the logic above with this here:

emupid="$(sed -n 4p /dev/shm/runcommand.info | tr -d '\\"' | tr '^$[]*.()|+?{}' '.')"
[[ -n "$emu_command" ]] && pkill -f "${emupid}" && sleep 9

That's it. :-)

Cheers.

[lilbud]

@meleu Me after reading that whole post

[meleu]

@lilbud this topic was created exactly to avoid this reaction on other people's topics. :-)

[cyperghost]

@lilbud You're welcome to ask and post things affecting bash :)

[lilbud]

@cyperghost OK, I have very little experience with code and zero experience with bash.

Where in the hell do I start?

[meleu]

@lilbud at prompt. Type echo "Hello World". ;-)

[lilbud]

@meleu So...echo is like a print command?

[cyperghost]

@lilbud
You start with

cd ~
touch hello.sh && chmod +x hello.sh && echo 'echo -e "Hello World\nThis is my 1. code in bash"' > hello.sh
./hello.sh

[cyperghost]

@meleu Upss..
Are we not in lesson #2?

[meleu]

@cyperghost Me after reading your tutorial:

[lilbud]

@meleu This was my reaction

[cyperghost]

@meleu The interesting part is this [[ "$(pgrep -P $emupid)" ]] && kill $(pgrep -P $emupid) it worked flawless in my testing. I just called a bash within a bash and they were properly detected!

Mausberry shutdown script v 1.58

#!/bin/bash
 
#this is the GPIO pin connected to the lead on switch labeled OUT
GPIOpin1=23
 
#this is the GPIO pin connected to the lead on switch labeled IN
GPIOpin2=24
 
echo "$GPIOpin1" > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio$GPIOpin1/direction
echo "$GPIOpin2" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio$GPIOpin2/direction
echo "1" > /sys/class/gpio/gpio$GPIOpin2/value
while [ 1 = 1 ]; do
power=$(cat /sys/class/gpio/gpio$GPIOpin1/value)
if [ $power = 0 ]; then
sleep 1
else
 
# End Emulationstation if condition of running binary is true (v1.58)
# v1.0 07/21/17 by cyperghost - Inital run 
# v1.1 07/22/17 - Added chown command to set right user permission for creating es-shutdown
# v1.2 07/23/17 - Some small improvments, easier to maintain, removed echo, removed else branch 
# v1.5 07/27/17 - Great step to exit ES even if emulators is running by runcommand.sh are started
# v1.55 07/29/17 - all kudos go to @meleu for his alltime genious RegEx hack!
# v1.56 07/30/17 - All emulators will be detected. This is a full functional code equal to developing v1.7
# v1.58 08/02/17 - generel method: Use PPID to detect child PIDs now (SCUMMVM fix)
# v1.7 is in work flow - This will be cleaner and better coded and is better to maintain
# I just checked with SSH command - it saved my metadata! Maybe you need to extend sleeptimer!
# greetings @pjft for his famous favorits and @meleu for his RegEx sniplets and his constant help! 
 
espid="$(pgrep -f "/opt/retropie/supplementary/.*/emulationstation([^.]|$)")"
if [[ -e "/dev/shm/runcommand.info" ]]; then
    emupid="$(sed -n 4p /dev/shm/runcommand.info | tr -d '\\"' | tr '^$[]*.()|+?{}' '.')"
    emupid="$(pgrep -f "$emupid")" 
fi
 
if [[ "$emupid" ]]; then
    [[ "$(pgrep -P $emupid)" ]] && kill $(pgrep -P $emupid)
    kill $emupid
    sleep 4
fi    
 
if [[ "$espid" ]]; then
   touch /tmp/es-shutdown && chown pi:pi /tmp/es-shutdown
   kill $espid
   exit
fi
# End Emulationstation if condition of running binary is true (v1.58)
 
sudo poweroff
fi
done
 

[meleu]

@cyperghost OMG, this -P is a key for a strong solution. Will post something when the kids go to bed! ;)

[cyperghost]

@meleu You would rather use pkill -P
as pgrep and pkill are using same synthax
But I stay to the basics and this is the PID number :D

I think it's now your turn to rearange and optimize the code a bit. You can also check your outfindings with the ES PID Detector - it now offers PIDs detected via PPID - it's a serious helper for such usecases.

[meleu]

@cyperghost
actually there's no need for what I was thinking. Your solution is really nice. :)

Maybe some code polishing can be made, but it worked flawlessly on my tests with ScummVM. Nice finding, bro!

[cyperghost]

@meleu Thank you mate. Was a nice piece of work anyway but pathed with pitfalls.
You should write some more tutorials - could be a good guidance.
But for now ... good night

[meleu]

@cyperghost said in shell scripting topic:

Was a nice piece of work anyway but pathed with pitfalls.

You gave me an idea!

[meleu]

@cyperghost
This is logically the same script, I just cleaned up the code (and bumped the version to v1.59): https://ghostbin.com/paste/adsrw

And this one is the PID detector: https://ghostbin.com/paste/f8tmt

Cheers!

[cyperghost]

Mausberry Shutdown Script 1.595

by @meleu and @cyperghost

Final version for PowerBlock users is here!

Mausberry users may get development to v1.7x

#!/bin/bash
# End Emulationstation if condition of running binary is true (v1.59)
# v1.0 07/21/17 by cyperghost - Inital run 
# v1.1 07/22/17 - Added chown command to set right user permission for creating es-shutdown // cyperghost
# v1.2 07/23/17 - Some small improvments, easier to maintain, removed echo, removed else branch // cyperghost
# v1.5 07/27/17 - Great step to exit ES even if emulators is running by runcommand.sh are started // meleu
# v1.55 07/29/17 - all kudos go to @meleu for his alltime genious RegEx hack! // meleu
# v1.56 07/30/17 - All emulators will be detected. // meleu
# v1.58 08/02/17 - generel method: Use PPID to detect child PIDs now (ScummVM fix) // cyperghost
# v1.59 08/03/17 - nothing new, just polishing the code // meleu
# v1.595 11/14/17 - Inserted newest emucall detection // meleu
# I just checked with SSH command - it saved my metadata! Maybe you need to extend sleeptimer!
# greetings @pjft for his famous favorits and @meleu for his RegEx sniplets and his constant help! 
 
#this is the GPIO pin connected to the lead on switch labeled OUT
GPIOpin1=23
 
#this is the GPIO pin connected to the lead on switch labeled IN
GPIOpin2=24
 
echo "$GPIOpin1" > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio$GPIOpin1/direction
echo "$GPIOpin2" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio$GPIOpin2/direction
echo "1" > /sys/class/gpio/gpio$GPIOpin2/value
 
while true; do
    power="$(cat /sys/class/gpio/gpio$GPIOpin1/value)"
    if [[ "$power" == 0 ]]; then
        sleep 1
    else
        # emucall="$(sed -n 4p /dev/shm/runcommand.info | tr -d '\\"' | tr '^$[]*.()|+?{}' '.')"
        emucall="$(sed '4!d; s/\([\\"]\|[[:alnum:]_]\+=[^ ]* \)//g; s/[][(){}^$*.|+? ]/\\&/g' /dev/shm/runcommand.info)"
        if [[ -n "$emucall" ]]; then
            emupid="$(pgrep -f "$emucall" | tr '\n' ' ')"
            pkill -P "$(echo $emupid | tr ' ' ',')"
            kill "$emupid"
            sleep 4
        fi    
 
        espid="$(pgrep -f "/opt/retropie/supplementary/.*/emulationstation([^.]|$)")"
        if [[ -n "$espid" ]]; then
            touch /tmp/es-shutdown && chown pi:pi /tmp/es-shutdown
            kill "$espid"
            exit
        fi
        # End Emulationstation if condition of running binary is true
 
        sudo poweroff
    fi
done
 

[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.