How can I write something into a file on an non-interactive shell?

I am relatively new to bash. I am trying to write something into a file using bash and Java.

In the interactive mode it works fine.

echo "Hello World" > new_file

But when I am, e.g. trying to execute this with help of the Java runtime nothing happens.

runtime.exec('echo "Hello World" > new_file');

doesn't work, while

runtime.exec('touch new_file');

works just fine.

Why is that and how can I make it work? Thanks in advance!

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What is @SOMETHING@ assigned to variable

Trying to read a bash noscript and I'm baffled with this construction. Never seen that before. Can some1 explain that to me?

https://redd.it/zd1rnx
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quotes from command output are treated as literal characters?

i'm trying to build a noscript that opens a dialog box with radio buttons, each button being assigned a name. these names can contain spaces, so obviously i try to quote the output from the array which contains the names.

when i run my current attempt, being

for n in ${!list@}; do
printf "$n "
printf "\"${list$n}\" "
done

it works as intended. it outputs the index of the name, followed by the name itself, in quotes.

giving it list=(test1 test2 "test 3") outputs 0 "test1" 1 "test2" 2 "test 3" which is exactly what i need.

so when i wrap this in a nice $() and use that as arguments for kdialog (or a quick testing noscript that loops through all cli arguments) i would expect the shell to treat the quoted parts as single arguments, rather than treating the quotes as literal characters. so when i make a noscript "test.sh" which contains

#!/usr/bin/bash
for item in $@; do
echo $item
done

and run it like this /test.sh $(for n in ${!list[@]}; do printf "$n "; printf "\"${list[$n]}\" "; done) i would expect to see

0
"test1"
1
"test2"
2
"test 3"

as output but instead i get

0
"test1"
1
"test2"
2
"test
3"

which leads me to believe that the shell is treating the quotes as literal. which sounds an awful lot like it's designed that way.

so is this supposed to happen? and is there a way around it?

i've already checked, single quotes don't work either.

https://redd.it/zd7axm
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Help with homebrew and bash

Hi everyone, I've changed my shell to the homebrew bash after installing homebrew in zsh. When I use "brew" it tells me that the command is not found. Is there some way to use both the homebrew bash and also be able to access homebrew while inside that bash?
Currently I am using the /opt/homebrew/bin/bash and it will not allow me to use the “brew” command.

Thank you!

https://redd.it/zdfrfp
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I trained an AI to understand and fix command-line errors

https://redd.it/zeafv1
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Bash syntax - why?

Hi folks,

I just came across the bash syntax for a switch statement. It's... surprising.

Are there any resources online that explain how this syntax came to existence, and why it is still in use today?

https://redd.it/zeepuh
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Hey y’all i’m super new to bashing and i’m curious on where to start. I know nothing about bash but i was going to ask if y’all have any resources to help me get started with it? thank you!



https://redd.it/zem5a0
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Here’s a playlist of 7 hours of music with NO VOCALS I use to focus when I’m coding /learning . Post yours as well if you also have one!

Spotify | Apple | Youtube | Amazon

https://redd.it/zelzee
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Replace hostname

Hi All,

I am planning to replace existing hostname by making simple interactive noscript

#!/bin/bash
echo "Set Hostname"
read name1
name='cat /proc/sys/kernel/hostname'
sed -i 's/$name/$name1/g' /etc/hostname
hostname $name1

The issue here is - it changes hostname. I exit and log back in. I see new hostname. But nothing gets changed in /etc/hostname file. reboot and I am back to old hostname.

​

What am I missing here?

https://redd.it/zexcn4
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Finding a 5 digit code for a locked zip file

As the noscript states, I am looking to create a noscript that goes through 0 to 99999 and once it finds the right code it unlocks and unzips the contents. I know the use of a for loop and it will be slow but that's nothing to worry about for my noscript. The locked file is using 7-zip.

https://redd.it/zey4h8
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Reading stdin of a parent process from within a child process?

# edit: Excellent solution by oh5nxo

{
coproc {
while read -sn1 -u3 line # original stdin
do
echo "coproc got $line" >&4 # original stdout
done
}
} 3<&0 4>&1 # hackery to "ship" stdin and stdout into coprocess
while sleep 1
do
echo "toplevel doing other things"
done

[https://www.reddit.com/r/bash/comments/zeyt4f/comment/iz9el4q/?utm\_source=share&utm\_medium=web2x&context=3](https://www.reddit.com/r/bash/comments/zeyt4f/comment/iz9el4q/?utm_source=share&utm_medium=web2x&context=3)

# Objective:

Reading `stdin` of the parent process ongoing from within a coproc child process.

* Can't use root
* Can't block the parent process
* Can't use `read` in the parent process because even if it's not blocking for long it's very messy and defeats the purpose of having an unhindered co-running process (see: `read` examples below).

# What I have:

ParentPid=$$
coproc {
exec 1>/proc/$ParentPid/fd/1 2>/proc/$ParentPid/fd/2
printf '\n%s\n' 'COPROC reading...' 2>&1
while true; do
read -n 1
printf 'KEY: >%q<\n' "$REPLY"
done
}

# Output should look like:

...the following when `asdf` is typed or sent into `stdin` of the parent process:

KEY: >a<
KEY: >s<
KEY: >d<
KEY: >f<

# Example output if something isn't working:

asdf

# Solutions that don't work:

/dev/stdin>/proc/$!/fd/0
# bash: /dev/stdin: Permission denied

/dev/stdin>&"${COPROC[1]}"
# bash: /dev/stdin: Permission denied

/proc/$$/fd/0>&"${COPROC[1]}"
# bash: /proc/13852/fd/0: Permission denied

# ___Inside coproc process___
exec /proc/$ParentPid/fd/0>&0
/bin/bash: line 3: exec: /proc/16449/fd/0: cannot execute: Permission denied

Works but blocks the parent process:

while true; do
read -s -n 1
echo -n "$REPLY" >&"${COPROC[1]}"
done

Works but it's sloppy, can leak text onto the tty and lags input if "do other things" takes too long:

while true; do
read -s -t 0.1 -n 999
echo -n "$REPLY" >&"${COPROC[1]}"
# do other things
sleep 0.5
done

Completely at the end of my rope on how to solve this, any help is greatly appreciated.

Big thank you,

https://redd.it/zeyt4f
@r_bash

what is this? !::=::\

Running env in bash in cygwin terminal shows this in my environment variables and I am ashamed to say I don't have any idea what it does or what it's for:

!::=::\

Any ideas?

https://redd.it/zf48j3
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I'm preparing for the LPIC-1 exam and I cannot figure out why the correct answers to this question are the marked ones. Can someone help me?
https://redd.it/zf6nte
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Why is the output in a different order?

declare -A beatles
beatles=(
singer=John
bassist=Paul
drummer=Ringo
guitarist=George
)

# Loop as written in the O'Reilly book

for musician in singer bassist drummer guitarist
do
echo "The ${musician} is ${beatles$musician}."
done
echo

# My way

for i in "${!beatles@}"
do
printf '%s\n' "The $i is ${beatles${i}}."
done

https://redd.it/zf7g2o
@r_bash

Hello guys! Im writing to here with the last hope. Im doing my first semester in uni and I have to write a bash noscript and I cant do it, I’Ve seen a lot of videos but I just simply dont understand it. I have 15 hours to make it so please, if anyone can help, help!

My homework is called Letter/Email Script (idk whice one, im not native english).
The denoscription to is:
“The program runs in the background and monitors incoming mail, if the subject of the mail is a certain pre-specified text (argument), then the
takes the contents of the letter as the sh shell noscript, executes it, and captures its output and sends it back to the sender. Don't disturb others during rehearsals”

I translated the dinoscription with google so Idk how accurate is it. :(

https://redd.it/zfdik9
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I'm writing a file manager in pure BASH

https://redd.it/zfiqrq
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Losing my mind trying to add to my startup noscript

Hi folks! I am working on setting up Robot Operating System on Ubuntu 22.04LTS. I need to add an echo line to my startup noscript, so that when I open my terminal it will automatically run a source command to setup the source for ROS.

I can't figure out how to do this - i've just been told that stuff about ~/.bashrc, which I opened in vim. I looked at it and i don't see where I would add the echo line. If anyone can provide advice, or point me towards a helpful resource, I'd greatly appreciate it.

Thanks in advance!

https://redd.it/zfh9p0
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Spoof MAC address to random Apple vendor and Change to random IP according to current network ID

# CREATED BY: Zerodark875
# PROOF OF CONCEPT

if [[ $(id -u) -ne 0 ]]; then
echo "Need root. Quiting."
exit 1
fi

if [[ -z ${1} ]]; then
echo "Usage: ${0} [network_device]\nExample: ${0} eth0"
exit 2
fi

net_dev=${1}
current_ip=$(ip addr show ${net_dev} | grep -w inet | awk -F' ' {'print$2'} | cut -f1 -d'/')
network_id=$(echo ${current_ip} | awk -F'.' {'print$1"."$2"."$3'})
current_mac=$(ip link show ${net_dev} | grep -w ether | awk -F" " {'print $2'})
apple_mac_addresses=$(macchanger --list=Apple | cut -f3 -d" " | awk {'if ($1 != ""){print$1}'})
apple_mac_address_length=$(wc -l<<<${apple_mac_addresses})
picked_apple_mac_address=$(expr $(expr ${RANDOM} % ${apple_mac_address_length}) + 1)
vendor_id=$(echo ${apple_mac_addresses} | awk -v line=${picked_apple_mac_address} -F" " {'print$line'})

final_mac_address="${vendor_id}:$(expr $(expr ${RANDOM} % 89) + 10):$(expr $(expr ${RANDOM} % 89) + 10):$(expr $(expr ${RANDOM} % 89) + 10)"
final_ip="${network_id}.$(expr $(expr ${RANDOM} % 254) + 1)"

echo "Generating new ip and Mac address with Apple as vendor ID ;)"
echo "Current IP: ${current_ip} Current MAC: ${current_mac}"
echo ${final_ip} ${final_mac_address}

echo -n "Apply changes to the machine? (N/y):"
read choice
c=$(awk {'print tolower($0)'} <<< ${choice})
if [[ ${c} == "y" ]]; then
echo "Changing mac address to ${final_mac_address}"
ip link set ${net_dev} down
macchanger -m ${final_mac_address} ${net_dev}
ip link set ${net_dev} up
echo "Mac address changed. Waiting 5 seconds for new IP from DHCP server then we change it again"
sleep 5
current_ip=$(ip addr show ${net_dev} | grep -w inet | awk -F' ' {'print$2'} | cut -f1 -d'/')
echo "Deleting current IP ${current_ip}"
ip addr del ${current_ip}/24 dev ${net_dev}
echo "Adding new IP ${final_ip}"
ip addr add ${final_ip}/24 dev ${net_dev}
fi

https://redd.it/zfreok
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clustercli command not found, but the command works under the user ?!

Hi,

I'm trying to add some commands to the bash noscript, and it does not seem to be work for some reason.

So I run this command whichi works fine if run manually.

su - mwp_admin
(in mwp_admin) clustercli -a config -i ~/inventory -t v-cluster -s airgap
(in mwp_admin) export KUBECONFIG=~/v-cluster"_config"
(in mwp_admin) kubectl exec -it v5-virtio-cuvnf-0 -n smcu2 -c cuvnf-container bash -- netstat -anp | grep sctp > result.csv

I wanted to add this to a shell noscript and run it. So I wrote this noscript, but its throwing error.

su - mwp_admin -c "clustercli -a config -i ~/inventory -t v-cluster -s airgap;export KUBECONFIG=~/v-cluster\"_config"\;kubectl exec -it v5-virtio-cuvnf-0 -n smcu2 -c cuvnf-container bash;netstat -anp | grep sctp > result.csv"

Error :

bash: clustercli: command not found

Any thoughts ?

https://redd.it/zfuwat
@r_bash

Reset terminal but keep scrollback buffer

Sometimes a program messes up the the terminal, and I have generally used reset to get things back into a normal state if I don't want to completely close the terminal window.

However this also tends to wipe/delete/clear the scroll back buffer.

Is there a way get the terminal back to default settings without wiping the scrollback history?

I know of the clear utility (and it has -x), but I'm not sure if it does the same reseting as reset. None of the options to reset(1) really seem to indicate to me reinitializing the terminal but keeping scroll history.

Thanks for any info.

https://redd.it/zg069a
@r_bash

Consult a “.txt” file and search if a certificate of a given URL its about to expire in certain year

Hi! I wanted to know if you guys would be able to help me on this exercise :)
I’m new on shell noscripting and I know only the basics of it.
However, I have this exercise in which I have to write 2 noscripts.

-The first one requires me to ask the user for an URL, and as an output, provide the expiration dates of a certificate, as well as automatically put that information on a .txt file named “dates.txt”

So far I have been able to do this first noscript and it runs well, where I’m having a little bit of trouble is on the second one.

-The second one asks me for this:

Consult the dates.txt file and search if the certificate of the given URL its about to expire in the 2018.

b) Create an "if/else" statement.
IF the cat command isn't empty (enddate/expiration date of the certificates is 2018), then you must save the information of expire of the URL in a "renew.txt" file assing the text "certificate will expire soon"
ELSE: echo "Nothing to do"

This is the part where I’m having a little bit of trouble with and I wanted to know if you could help me do it, thanks!

https://redd.it/zgakf1
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