Linux bash practice site

HI, I am preparing for OSCP and hence I am learning bash.
Can someone please suggest me a best place to practice bash(For linux).
Any online link would be helpfull

https://redd.it/10o0z6g
@r_bash

What is wrong with this noscript?

Trying to grep an array of strings from a file on a remote server but the noscript does seem to do it, I might be missing quotes or the use of array is wrong here?

PARAMS=(“abc” “xyz” “ijk”)
REMOTEFILE=“pathtoFile”
NODES=(“srv1” “srv2”)

for srv in “${NODES@}”
do
ssh $srv << EOF
grep -f “${PARAMS@}” $REMOTEFILE >/path/remotefile.txt
EOF
done

https://redd.it/10nxxc0
@r_bash

Cannot backup a directory with tar. When i am trying to run the noscript it says "Cannot stat: No such file or directory". What is the problem? How to resolve it? Or maybe there is some other way to backup a directory. Please help

https://redd.it/10o3h0k
@r_bash

How can I modify this bash command that will also output the content of the given file.
https://redd.it/10o2qi5
@r_bash

What is the fastest way to read groups of N lines from stdin / a pipe?

Im trying to figure out a good, efficient and reliable way to read groups of N lines at a time from stdin or (more generally) from a pipe. Id like to accomplish this without needing to save (or wait for) the entire contents of stdin into a variable. So far the only reliable way Ive found to do this involves something like:

nLines=8 # change as needed
while true; do
outCur="$(kk=0; while (( $kk < $nLines )); do read -r </dev/stdin || break; echo "$REPLY"; done)"
[ -z $outCur ] && break || echo "$outCur"
done # | <...>

That said, if reading the entire pipe, there are some options that are much faster than read. I wrote a little speedtest to test a few:

fgg() { while read -r; do echo "$REPLY"; done | wc -l; }
fhh() { cat | wc -l; }
fii() { head -n $1 | wc -l; }
fjj() { echo "$(</dev/stdin)" | wc -l; }
fkk() { wc -l </dev/stdin; }
fll() { mapfile -t inLines </dev/stdin; printf '%s\n' "${inLines@}" | wc -l; }
fmm() { inLines="$(</dev/stdin)"; echo "${inLines}" | wc -l; }

# note: fll and fmm dont meet the "dont save the full stdin to a variable" criteria

nLines=100000

for fun in fgg fhh "fii $nLines" fjj fkk fll fmm; do
declare -f "${fun% }"
echo
time seq 1 $nLines | $fun
echo
echo '----------------------------------'
echo
done

Which, on my test system, produces

fgg ()
{
while read -r; do
echo "$REPLY";
done | wc -l
}

100000

real 0m5.780s
user 0m3.655s
sys 0m4.306s

----------------------------------

fhh ()
{
cat | wc -l
}

100000

real 0m0.086s
user 0m0.077s
sys 0m0.028s

----------------------------------

fii ()
{
head -n $1 | wc -l
}

100000

real 0m0.085s
user 0m0.107s
sys 0m0.000s

----------------------------------

fjj ()
{
echo "$(</dev/stdin)" | wc -l
}

100000

real 0m0.124s
user 0m0.117s
sys 0m0.039s

----------------------------------

fkk ()
{
wc -l < /dev/stdin
}

1000001

real 0m0.085s
user 0m0.094s
sys 0m0.000s

----------------------------------

fll ()
{
mapfile -t inLines < /dev/stdin;
printf '%s\n' "${inLines[@]}" | wc -l
}

100000

real 0m2.241s
user 0m1.064s
sys 0m2.331s

----------------------------------

fmm ()
{
inLines="$(</dev/stdin)";
echo "${inLines}" | wc -l
}

100000

real 0m0.185s
user 0m0.180s
sys 0m0.039s

This suggests (on my test system) in a worst-case scenario (i.e., many many inputs and most of the time spend looping the `read` command), `read` is about 75x slower than optimal, loading the lines into an array is \~25x slower than optimal (+ more memory usage), and saving the full input into a (non-array) variable is \~2x slower than optimal (+ more memory usage).



From this test, using head -n in a loop seems like the obvious optimal answer, but when I try this I get....strange behavior...

seq 1 1000 | {
head -n 10
head -n 10
head -n 10
}

produces


0
1
2
3
4
5
6
7
8
9
284
285
286
287
288
289
290
291
292
293
540
541
542
543
544
545
546
547
548
549

Playing around with different sized input lines suggests that on every subsequent call after the 1st on the same pipe, head -n throws away the 1st kilobyte worth of input lines. Perhaps it is trying to "skip" reading a 1kb pipe header of some sort, but since it isnt at the start of the pipe it throws away data instead? If anyone knows how to stop head -n from doing this

please let me know. Or if there is some other quick way that I havent tested here please do suggest it.

Thanks in advance.

https://redd.it/10odhbo
@r_bash

Random Joke generator

Small bash file to tell a random joke. (100+ available!)

&#x200B;

\#!/bin/bash

\#mmartin.,29/01/23, Purpose:Print a random joke

awk '

BEGIN{ srand() }

rand() * NR < 1 {

line = $0

}

END { print line }' \~/Documents/VariousTexts/jokes.txt

exit

&#x200B;

Download from my github

github.com/myklmar/noscripts with jokes.txt file.

https://redd.it/10oc0a4
@r_bash

GitHub - awesome-lists/awesome-bash: A curated list of delightful Bash noscripts and resources.
https://github.com/awesome-lists/awesome-bash

https://redd.it/10ozsm8
@r_bash

How can I execute bash commands from a string ?

Something like this:

cmd="Hello World! | cat -"
$cmd

https://redd.it/10p316j
@r_bash

Thank you

I don’t post much but I do lurk around looking to learn. From beginner to expert questions everyone is very helpful. Just wanted to say thank you to the community.

BTW will be cross posting to r/commandline because they are a great community as well.

https://redd.it/10p3tia
@r_bash

How to filer partial matches that do not end in certain characters

first time posting, forgive me


Basically I want to filter output to go from something like this:


mate-desktop-common
gedit
gedit:i386


to this


mate-desktop-common
gedit:i386


How would I do that?

https://redd.it/10p6duw
@r_bash

exit terminal without closing the program / headless mode

Hi there!I run this noscript:

#! /bin/sh.
waydroid session stop
weston --width=555 --height=875 -Swayland-droid & WAYLAND_DISPLAY=wayland-droid waydroid show-full-ui

The goal is to open weston, which will start waydroid in that window size. Everything works fine, but I'd like to hide or exit the terminal and only show the weston window. (Like headless mode)? How could I achieve this?

https://redd.it/10pd91w
@r_bash

How do you copy the folder structure of a folder and paste it in a new folder?

How do you copy the folder structure of a folder and paste it in a new folder? I have a folder with a lot of subfolders that contains a lot of subfolders, and I would like to copy the folder structure so I don't have to do it manually. Is there any command for this?

https://redd.it/10ppmtr
@r_bash

Print just first lines beginning with "> " via sed doesn't work

Hi! Here is my input file:

#

> Check file types and compare values
> Returns 0 if the condition evaluates to true, 1 if it evaluates to false
> More information: https://www.gnu.org/software/bash/manual/bash.html#index-test

- Test if a given variable [is equal/not equal to the specified string:

[ "${string value: variable}" {string value: ==|!=} "{string value: string}" ]

Here is my noscript:

#!/usr/bin/env bash

declare file="/home/emilyseville7cfg/Documents/mine/other/cli-pages/common/.btldr"

sed -nE '/^>/ {
h

:denoscription
N
H
/> (Aliases|See also|More information):/! bdenoscription
s/^.*\n//
x
p
Q
}' "$file"

I wanna print just all lines beginning with `> ` but not including `(Aliases|See also|More information):` at the beginning. I expect such lines to be in the pattern buffer at the end of the noscript but surprisingly I get this output:

> Check file types and compare values
> Check file types and compare values
> Returns 0 if the condition evaluates to true, 1 if it evaluates to false
> Check file types and compare values
> Returns 0 if the condition evaluates to true, 1 if it evaluates to false
> More information: https://www.gnu.org/software/bash/manual/bash.html#index-test

Note that hold space should contain `> More information: https://www.gnu.org/software/bash/manual/bash.html#index-test` at the end of the noscript.

My idea was to condense all lines starting with an angle bracket in the pattern space excluding the last one containing `(Aliases|See also|More information):`. What am I missing to implement what I want?

[https://redd.it/10pwd8q
@r_bash

Can I do -this- using a bash noscript?

I have a fee Lua driver files that use libraries. I need to provide context for any use of these libraries in the file so that all the logic is contained in one file. Can I accomplish that using a bash noscript? All files will be stored locally.

https://redd.it/10qdrc8
@r_bash

Bash noscript to invoke conda environment

I'm trying to write a bash noscript for executing a set of commands to activate my conda env


#!/bin/csh

source ~/.cshrc

module load anaconda3/4.2.0

source <path>/conda.csh

conda activate myenv1

however post the noscript execution, I expect myenv1 to be activated but that fails to happen, why is that? and what can I do to fix it?

https://redd.it/10qn164
@r_bash