Is there something like w3school but for bash? or any other shell?

I'm looking for an online resource for learning shell noscripting. I dont really find youtube lessons helpful so written material works better for me. Books could also work tbh but no video plz :D

https://redd.it/z68zbh
@r_bash

I'm currently taking a Google Cloud Course that includes Qwiklabs. I've been tasked with translating one of the labs into a linux bash noscript. I've done that but i'd like someone who knows what they're doing to take a look at it before i turn it in. I'd really appreciate it. Thanks in anticipation.

I'm currently a big noob trying to wrap my head around tech. please be nice

https://redd.it/z6ala6
@r_bash

What does this noscript do? I need to explain what this noscript does for a question on my classwork but my teacher isn't satisfied with my answer. Can anyone provide some insight into what exactly is happening with this noscript?
https://redd.it/z6c7x0
@r_bash

Getopts to allow only 1 option

How can I make getopts to allow only one option?

while getopts ":ab" option
do
case $option in
a)
echo "test1"
;;
b)
echo "test2"
;;
esac
done

This is an example loop, running the noscript

./noscript.sh -a -b

will return both a and b cases. How can I make it to show an error message instead?

https://redd.it/z6hq3c
@r_bash

printf with colour using variable

I thought i was being clever using printf with colour variables to save me typing out the colour i'd like, but apparently shellcheck doesn't like that

for instance...

red="\e1;31m%s\e[0m\n"
green="\e[1;32m%s\e[0m\n"
yellow="\e[1;33m%s\e[0m\n"

and then

printf "$red" "string of sorts in red colour"

Since it complains, is there another way, or just suppress and ignore it (i've been ignoring it up until now since i discovered shellcheck, and never run into any problems)? Thought i'd ask just in case it does fluff something up i'm unaware of.

[https://redd.it/z6vhvv
@r_bash

eval vs source

I recently discovered that you can get functionality similar to eval ... with source <(...).

There is some difference in functionality - mostly that eval can be used within some code statement whereas source <(...) requires complete statements. e.g. in someFunction $(eval $someCode) the eval ... cant be replaced with source <(...). The flip side of this is that source <(...) will evaluate everything between the paranthesies, whereas eval will stop evaluating at pipes/newlines/semicolons.

Any other considerations regarding these two that are worth knowing?

Side note: I'm not advocating using these for "general noscripting", but there are some situations where they are useful. Examples of what Id call "reasonable usage" for both are:

eval ...

for nn in $(eval echo {$start..$end..$skip}); do
    <...>
done

Yes, I know you can do

nn=$start
while [ $nn -le $end]; do
    <...>
    nn=$((( $nn + $skip )))
done

but its just an example

source <(...)

# passing an array to a noscript
declare -p arrayName | noscript.sh

# in noscript.sh
source <(cat)

https://redd.it/z6wm7f
@r_bash

New to Bash

Hey everyone...

I'm super new to bash noscripting, I'm working through a class currently and I am stuck. I need help, I'm trying to isolate a particular word and print out the results.

Would I be using awk then pipe and wc? For example, this particular scenario involves searching for individuals who are creating a loss of profit. I need to isolate the people responsible and print it to a new evidence file. I think I just don't have enough practice to understand it yet, any help would be appreciated! If you are curious and want to see the exact code DM me for it.

https://redd.it/z6zq0g
@r_bash

This is my first bash noscript! What do you think? You plug in your droplet ip, your domain and your gitlab info and in 5 minutes your web app is live at https://yourdomain, and all future commits to main are automatically deployed. Included templates for new django, flask and fastApi projects!
https://github.com/johnsyncs/ezinnit

https://redd.it/z74xq9
@r_bash

hfetch, a simple and minimal system information tool written in bash. with fortune
https://redd.it/z776ux
@r_bash

associative array order

I've noticed, while playing around with associative arrays, that when I append keys/values, the appended pairs stay in the order I added them in stdout, unlike the key/value pairs I declared the array with. If that's the case, can I take advantage of that in order to control the way associative arrays are displayed?

https://redd.it/z7bcmb
@r_bash

Script to detect change in URL redirection:

I've been hesitant to submit this in fear that I have re-invented the wheel here, but please tell me if I have.

#!/usr/bin/env bash

# Script to be placed in /etc/cron.d/cron.hourly

###############################################################################################################
# Ignore below comment, it's just for shellcheck. (Must appear before any instructions.) #
# shellcheck disable=SC1090 # Can't follow non-constant source #
# shellcheck disable=SC2034 # Yea, I have some unused variables #
###############################################################################################################

requiredPackages=(
alsa-utils
coreutils
curl
wc
wget
zenity
)

noscriptBasename=$(basename "${0}") # Could also user ${BASH_SOURCE[0]} here.
kibibyte="1024"
mebibyte="$(( kibibyte * kibibyte ))"
###############################################################################################################
########################################### Configuration Variables: ##########################################
###############################################################################################################

### Inputs: Wikipedia example ######################################################################################
user="user"
workingDir="/home/${user}/${noscriptBasename}"
audioOutputDevice="plughw:CARD=NVidia,DEV=3" # Get list of available devices with: aplay -L | grep "CARD"
maxLogSize="$((1 * mebibyte))" #bytes
notificationSound="${workingDir}/notify.wav"
urlToWatch="https://en.wikipedia.org/wiki/Redirect_page" # Will redirect to https://en.wikipedia.org/wiki/URL_redirection
notificatonTitle="Redirect change"
notificationMsg="Page now points somewhere new!" # String will be followed by redirect URL and location noscript is run from.
subredditsInput="${workingDir}/subreddits" # If present, is a sourced bash noscript that should define a ${subreddits[@]} array.

### Outputs: ##################################################################################################
logFile="${workingDir}/${noscriptBasename}.log"
lastRedirectFile="${workingDir}/lastRedirect"
subredditList="${workingDir}/subreddits.list"
website="${workingDir}/${noscriptBasename}.html"
sharedMemory="/dev/shm/${noscriptBasename}.shm"
namedPipe="/dev/shm/${noscriptBasename}.pipe"

###############################################################################################################
################## No need to modify anything below this line unless changing functionality ###################
###############################################################################################################
version="4" #Version 4 outputs to subreddits.list instead of subreddits.
version="5" #Version 5 reads subreddit array from subreddits file.

# Defines checkError(), which simply converts an exit code to a string denoscription.
# https://old.reddit.com/r/linuxquestions/comments/6nuoaq/how_can_i_look_up_exit_status_codes_reliably/
if [ -f "/home/${user}/.adms/ADMS-OS/noscripts/CommonScripts/error" ]; then
source "/home/${user}/.adms/ADMS-OS/noscripts/CommonScripts/error"
fi

###############################################################################################################
################################# Ideas for extending functionality: ##########################################
###############################################################################################################
# TODO: Should I install required packages if missing ???
###############################################################################################################
# Do I really want to make a distro indepandent check here?
# A lot is already done in "/home/${user}/noscripts/CommonScripts/packages"
# But no, I really don't....
# for package in

"${requiredPackages[@]}"; do
# :
# done
###############################################################################################################
# TODO: Should we use a named pipe for communication with subprocess instead ???
###############################################################################################################
# Would have to re-do a lot of logic for this route.
# if [ ! -p "${namedPipe}" ]; then
# mkfifo -m "a=rw" "${namedPipe}" #Man page literally says "not a=rw", but what does that mean?
# fi
###############################################################################################################
# TODO: Use array of URL's for tracking multiple websites.
###############################################################################################################
# Don't actually need this at all right now, but maybe one day...
###############################################################################################################

#Does not try to handle race-conditions, but I don't think it should not be a problem.
declare -A globalState;

function setGlobalState()
{
local -r varName="${1}"
local -r varValue="${2}"

if [ ${#} -eq 2 ]; then
globalState["${varName}"]="${varValue}"
fi

printf "# Using associative array for easy addition of new variables\n" | sudo tee "${sharedMemory}" > /dev/null
declare -p globalState | sudo tee -a "${sharedMemory}" > /dev/null
}

function getGlobalState()
{
local -r varName="${1}"
local -r varType="${2}"
local success=true
if [ -f "${sharedMemory}" ]; then
source "${sharedMemory}"
if [ ${#} -ge 1 ]; then
if [[ "${globalState[${varName}]}" != "" ]]; then
printf "%s" "${globalState[${varName}]}"
else
success=false
fi
fi
else
success=false
fi

if ! ${success}; then
if [[ ${varType} == "bool" ]]; then
printf "false";
elif [[ ${varType} == "int" ]]; then
printf "0";
elif [[ ${varType} == "string" ]]; then
printf "";
fi
return 1
fi
return 0
}


function cleanupSharedMemory()
{
if [ -f "${sharedMemory}" ]; then
sudo rm -vf "${sharedMemory}"
fi
}

setGlobalState "ring" "false"

dateFmt="+%Y.%m.%d_%I:%M%P"
#dateFmt="+%Y-%m-%d_%H:%M:%S.%3N"
function getDateTimeStamp()
{
date "${dateFmt}"
}

function getLogSize()
{
wc -c "${logFile}" | cut -f 1 -d ' '
}

function getLogLength()
{
wc -l "${logFile}" | cut -f 1 -d ' '
}

function log()
{
local -r extFmt="${1}"
printf "%s | ${extFmt}\n" "$(getDateTimeStamp)" "${@:2}" | tee -a "${logFile}"
}

function truncateLog()
{
local -r percentToKeep="${1}"

local -r logSize="$(getLogSize)"
local -r numLinesStart="$(getLogLength)"
# shellcheck disable=SC2155 # Masking return values by declaring and assigning together.
local numLines="$(echo "scale=0; ${numLinesStart} * ${percentToKeep}" | bc)"
numLines="${numLines%.*}" #Round down to nearest int.

# shellcheck disable=SC2005 # It's not a useless echo! It's not! I love echo...
echo "$(tail "-${numLines}" "${logFile}" 2> /dev/null)" > "${logFile}"

log "Trimmed output size: %b -> %b" "${logSize}" "$(getLogSize)"
log "Trimmed output size: %b -> %b" "${numLinesStart}" "$(getLogLength)"
}

printf -v dividerVar "<%.0s>%.0s" {1..80}
function divider()
{
printf "%b\n" "${dividerVar}">> "${logFile}"
}



function ringer()
{
local -r startVolume=$(amixer get Master | grep -o "[0-9]*%" | head -1) #Record current volume level
# shellcheck disable=SC2034 # The variable ${uid} is used when testing as cron job.
local -r uid=$(id -u "${user}")
local ring=true #Should always be true fist call.
if [[ "$(getGlobalState "ring")" != "${ring}" ]]; then
printf "Ringer was called with incorrect ring state! Check logical flow!\n"
fi

while ${ring}; do
amixer set Master 20% > /dev/null #I use headphones, and I don't want to blast out my eardrums

# Ok, weird one. Audio will not play over

same device user is using, so we need to specify a different one.
# So, if user is using laptop speakers, we can play though properly equipped external HDMI montior.
# Also, the audio is muted for the first second of play, so we will play the sound twice, but hear it once.
sudo -H -i -u "${user}" "aplay" -D "${audioOutputDevice}" "${notificationSound}" "${notificationSound}"

# This version works if run by user directly (i.e. Not as cron job)
# aplay -D "${audioOutputDevice}" "${notificationSound}" "${notificationSound}" > /dev/null

amixer set Master "${startVolume}" > /dev/null #Reset volume to what it was before
sleep 1
ring=$(getGlobalState "ring" "bool")
done
setGlobalState "ring" "false"
}

function popup()
{
local -r website="${1}"
local -r width=400
local -r height=200
local -r noscript="${notificatonTitle}"
local -r message="${notificatonMsg}\n${1}\nThis dialoge was created by: $(realpath "${BASH_SOURCE[0]}")"

zenity \
--warning \
--text="${message}" \
--noscript="${noscript}" \
--width="${width}" \
--height="${height}"
}

function checkReDirect()
{
local -r lastRedirect="$( < "${lastRedirectFile}" )"
local currentRedirect=""

currentRedirect="$(curl -ILs -o /dev/null -w "%{url_effective}" "${urlToWatch}")"
curlCode="${?}"
if [ "${curlCode}" -ne 0 ]; then
if [[ "${ERROR_SOURCED}" == "true" ]]; then
log "$(checkError "curl" "${curlCode}")"
else
log "Error! curl failed with ${curlCode}"
fi
return
elif [[ "${currentRedirect}" == "${lastRedirect}" ]]; then
log "Executing: %b ( No news... )" "$(realpath "${BASH_SOURCE[0]}")"
return
else # This isn't needed since other cases do early return ...
log "Executing: %b ( NEWS!! )" "$(realpath "${BASH_SOURCE[0]}")"
listSubreddits
wget "${currentRedirect}" -O "${website}" # Grab page for analysis

redirectEnding=${lastRedirect%/} # Remove trailing slash if present
redirectEnding=${redirectEnding##*/} # Remove everything up to last slash (Shoud be left with last section of URL)

noscriptSuggestion="$(grep -o "<noscript>.*</noscript>" "${website}")" #TODO: Find better way to parse html
noscriptSuggestion="${noscriptSuggestion#*>}" # Strip off <noscript>
noscriptSuggestion="${noscriptSuggestion%<*}" # Strip off </noscript>
log "Title Suggestion: ${redirectEnding} - ${noscriptSuggestion}"

log "Opening %s\n" "${currentRedirect}"
printf "%s" "${currentRedirect}" > "${lastRedirectFile}"


setGlobalState "ring" "true"
ringer & # Non-blocking so it will keep ringing until killed.
ringerPID=${!} # Keep this as global variable.

#Attempt to open URL in default web-broswer
if command -v gnome-open > /dev/null; then
gnome-open "${currentRedirect}" &
[ -f "${subredditList}" ] && [ -s "${subredditList}" ] && gnome-open "${subredditList}" &
elif command -v xdg-open > /dev/null; then
xdg-open "${currentRedirect}" &
[ -f "${subredditList}" ] && [ -s "${subredditList}" ] && xdg-open "${subredditList}" &
elif command -v gio > /dev/null; then
gio open "${currentRedirect}" &
[ -f "${subredditList}" ] && [ -s "${subredditList}" ] && gio open "${subredditList}" &
fi

popup "${currentRedirect}" # Blocking command. Once popup is closed, we will kill the ringer.
setGlobalState "ring" "false" # Seems /dev/shm is the way to communicate with background processes.
printf "Popup closed. Waiting for ringer to end. [pid=%s]\n" "${ringerPID}"
wait "${ringerPID}"
printf "Ringer ended.\n"
fi
}

function listSubreddits()
{
# Maybe one of these subreddit will care about the URL change
if [ -f "${subredditsInput}" ]; then
# Expected format is simply to define an array named ${subreddits[@]}
# You can form that array however you want. Keep it simple, or go nuts.
source "${subredditsInput}"
fi

for subreddit in "${subreddits[@]%\/}"; do # Normalize sub names

by removing trailing slash if present.
subreddit="${subreddit##*\/}" # Normalize sub names by removing any subreddit prefix.
printf "https://old.reddit.com/r/%s\n" "${subreddit}"
done > "${subredditList}"
}


###############################################################################################################
############ Script Start #####################################################################################
###############################################################################################################

divider

# To list hourly noscripts that run.
# sudo run-parts --report --test /etc/cron.hourly
# If started as root, then re-start as "${user}": (https://askubuntu.com/a/1105580)
if [ "$(id -u)" -eq 0 ]; then
log "Refusing to run as root!"
#exit; #Don't run as root.
exec sudo -H -u "${user}" bash -c "${0}" "${@}" #Force run as user.
echo "This is never reached."
fi

# ${DISPLAY} is typically unset when root sudo's to user.
if [ -z "${DISPLAY+unset}" ]; then
export DISPLAY=":0.0"
fi

log "Running as \${USER}=${USER} id=$(id -u). Script version = ${version}"

function exitCron()
{
printf "Exiting due to interrupt\n" >> "${logFile}"
if [ -n "${ringerPID}" ] && ps -p "${ringerPID}" > /dev/null; then
kill -15 "${ringerPID}"
fi

# unset traps.
trap - SIGHUP
trap - SIGINT
trap - SIGQUIT
trap - SIGTERM

cleanupSharedMemory
exit 1
}

#Don't think this is nessesary, but just make sure we exit each process when told to.
trap exitCron SIGHUP SIGINT SIGQUIT SIGTERM

if [ ! -d "${workingDir}" ]; then
mkdir -p "${workingDir}"
fi

# For loop will excute once every 600 seconds (10 minutes) for an hour
# shellcheck disable=SC2034 # Not using variable ${i}
for i in {0..3599..600}; do
checkReDirect
#break; #Uncomment to run once for testing.
sleep 600;
done

logSize="$(getLogSize)"
#Trim log length by about 10% if we have gone over ${maxLogSize}.
if (( "${logSize}" > "${maxLogSize}" )); then
truncateLog "0.90"
fi

cleanupSharedMemory

###############################################################################################################
# References:
#
# Check if variable is empty or unset:
# https://stackoverflow.com/questions/3601515/how-to-check-if-a-variable-is-set-in-bash
# https://www.cyberciti.biz/faq/unix-linux-bash-noscript-check-if-variable-is-empty/
#
# Send variable to background process:
# https://stackoverflow.com/questions/13207292/bash-background-process-modify-global-variable
#
# Limit log size keeping last n lines:
# https://unix.stackexchange.com/questions/310860/how-do-you-keep-only-the-last-n-lines-of-a-log-file
#
###############################################################################################################

https://redd.it/z7endd
@r_bash

Press ctrl z and type bg from a bash noscript automatically

So i have a timer i run from telegram connected to my pc. Do anyone know if there is a possibility to automatically stop the noscript and ”automatically” put it under ”jobs” without ”&” when started.
Currently i have to manually press ctrl z and then type bg

https://redd.it/z7avv4
@r_bash

pass to xargs

Hello I'm trying to process the output of \.

I run: mynoscript * to process all files in the current directory.

The output should be the full path of *.

This is what I have (not working):

echo ${@:1} | tr '\n' '\0' | xargs -0 -I "%" realpath "%"

can someone help?

https://redd.it/z7r0aj
@r_bash

How to make tests in .bashrc so they execute as fast as possible?

I am using this snippet from an AskUbuntu post in my own .bashrc, but would like to improve it so it works also in a tmux session:

if "$color_prompt" = yes ; then
# when system is accessed via SSH, hostname with light grey background
if [ $(pstree -s $$) = *sshd* ]; then sshbg="[\03348;5;7m\"; fi
# when used as root, change username to orange and '#' to red for prompt
if $(id -u) -eq 0 ; then usercol="[\03338;5;3m\"; hashcol="[\03338;5;1m\"; else usercol="[\03338;5;2m\"; fi
# bash PS1 prompt
PS1="${usercol}\u[$(tput sgr0)\]@[$(tput sgr0)\][\03338;5;4m\${sshbg}\h[$(tput sgr0)\]:[$(tput sgr0)\][\03338;5;6m\\w[$(tput sgr0)\]${hashcol}\\$ [$(tput sgr0)\]"
unset sshbg rootcol hashcol
fi

I can test similar to line 3 above if pstree -s $$ returns tmux: server, and if it does, I can test [[ $(pstree -s $(pgrep "tmux: client")) = *sshd* ]] to get the desired result.

So far, I have:

if "$color_prompt" = yes ; then
# when system is accessed via SSH, hostname with light grey background
if [ $(pstree -s $$) = *sshd* ]; then
sshbg="[\03348;5;7m\"
elif [ $(pstree -s $$) = *"tmux: server"* ]; then
if [ $(pstree -s $(pgrep "tmux: client")) = *sshd* ]; then
sshbg="[\03348;5;7m\"
fi
fi
# when used as root, change username to orange and '#' to red for prompt
...

Is there any better, especially faster way? Since it generates PS1, I would like it to be as fast as possible to not be annoying.

https://redd.it/z8033h
@r_bash

read command removes empty lines

#!/usr/bin/env bash
ls ??-??.json | while IFS= read -r line; do ./noscripts/add-missing-strings.js "$line"; done

What I have already tried:-played with ifs-read -r-started questioning if the problem is really here and not in the .js

All files - https://github.com/RDKRACZ/for-reddit/tree/main/noscripts

https://redd.it/z8955d
@r_bash

Is there any way to have a "longterm history" in addition to the normal history?

I like to keep a record of all the commands I have run on my VPS, because it's a good reference for how I installed or configured something many months ago. So I have my

HISTFILESIZE=10000, and HISTSIZE=10000

along with

export PROMPTCOMMAND="history -a; history -c; history -r;$PROMPTCOMMAND"

to keep the history file up to date after each command. But my command item numbers are in the 5000's now, so it's a little inconvenient to search through such a long history when I'm looking for something I just used a few days ago. Is there any way to to write to a file like .historylong in addition to my normal history? That way I could keep my normal history shorter and only reference the "indefinite history" when needed. And would there be any way to have .historylong displayed with a command line number that I could use in the infrequent times that I want to run something from long ago like:

!4573

https://redd.it/z8vubd
@r_bash

Why does sed delete the file's content when an output redirection is performed on the file, and not when using the append >> redirection?

For example, assume file.txt has the following content:

This is an example.

When I invoked the following command sed '/s/example/EXAMPLE/' file.txt > file.txt, the file's content was deleted.

But invoking this command sed '/s/example/EXAMPLE/' file.txt >> file.txt, produces the following output:

This is an example.
This is an EXAMPLE.

Isn't the output of sed produced on the stdout, and then the redirection operator redirects that output and rewrites the file?

https://redd.it/z8x9c8
@r_bash

Any way to keep the path context while running bash noscripts in other bash noscripts?

Im trying to make a noscript that will automate the process for running a server for a game "Unturned". My noscript only has this line of code:

su - steam -c "./Steam/steamapps/common/U3DS/ServerHelper.sh +LanServer/MyServer"

where it runs a file as the steam user in the steam user home directory, which inside that file, the last line runs:

./UnturnedHeadless.x8664 -batchmode -nographics "$@"

which SHOULD run the Unturned_Headless.x86_64 file, but doesnt, instead giving this error:

./Steam/steamapps/common/U3DS/ServerHelper.sh: line 18: ./UnturnedHeadless.x8664: No such file or directory

that file that its looking for being in the same folder as ServerHelper.sh . Im guessing that this is due it somehow not keeping the context of what dir its in while running the ServerHelper.sh file. Anyone know how i could fix it? (also, sorry if im making any dumb mistakes, ive never done any bash noscripting before)

https://redd.it/z8wzei
@r_bash