Questions tagged [subshell]
The subshell tag has no usage guidance.
216
questions
4
votes
2
answers
784
views
I need to have each line of a file run in a subshell of its own
I have a script that works fine, but runs in series.
I would like to have the script take each line from a text file and run/spawn that line in a subshell and then move onto the next line and so on.
I ...
- 141
0
votes
1
answer
45
views
How can I detect if I am in subshell, in bash and ZSH?
This question is different from In Bash, how can I detect if I'm in a subshell? because it's not shell specific.
Let's say I open a terminal, which is zsh. I can go deep into that like this,
$ ...
- 26k
0
votes
2
answers
48
views
Passing a variable to subshell
Contrived example:
#!/usr/bin/bash
MYVAR=$(cat /somedir | grep -i myval)
Now I want:
#!/usr/bin/bash
BASEDIR=/somedir
MYVAR=$(cat [BASEDIR?] | grep -i myval)
How should variable be passed to ...
- 218
0
votes
1
answer
23
views
How does a trap affect external programs?
When a subshell is entered, traps that are not being ignored shall be set to the default actions
Source: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_28
Apparently,...
- 2,260
9
votes
2
answers
933
views
Can a script be run as a subshell?
Scripts typically start with a shebang such as #!/usr/bin/env bash, which specifies the shell to be used for execution. The execution behavior when the shebang is not present seems to be up to the ...
- 2,133
0
votes
1
answer
174
views
How to curl/wget a script, run it with arguments, and make its functions available locally?
This function will either use cURL or wGet to download a script and execute it with additional arguments:
wexec() {
url=$1
shift
if command -v "curl" >/dev/null 2>&1; ...
- 197
0
votes
1
answer
96
views
error handling in a bash subshell
I'm writing some bash code, and I'd like the script to exit if there's any error. The set -e trick works pretty well, but not with subshells. Here's a simplified example:
set -e
chmod a=r file.txt
x=`...
- 31
0
votes
1
answer
58
views
Bash: is it possible at all to trap SIGTERM (or other) in a subshell?
Consider multiple subshells, each writing its own log file. Consider that one subshell failed, leading to sending (using some mechanism) of SIGTERM to all the subshells. Upon reception of SIGTERM all ...
- 457
1
vote
1
answer
44
views
Bash: how to check if any subshell failed?
Consider this code:
job()
{
local id=$1
sleep $id
}
do_job_in_parallel()
{
local pids=()
# run subshells
for id in $(seq 4)
do
job $id &
pids=("${pids[@]}" $!)
...
- 457
0
votes
1
answer
148
views
Cannot Display Bash Functions within FZF Preview Window
How do I get the FZF Preview Window to Display Functions from my Current Bash Environment?
I want to list my custom bash functions using FZF, and view the code of a selected function in the FZF ...
- 195
2
votes
1
answer
182
views
Capture output of a command that get stuck
I am trying to use regex for capturing some text pattern in an ouput of a command and create an array list_mqs. The problem is that this previous command get stuck and never terminates. So, when I use ...
- 23
0
votes
0
answers
30
views
$(declare -p) keeps adding backslashes
From help declare:
-p display the attributes and value of each NAME
Just running declare -p works as expected. So does running it in a subshell with (declare -p).
However, when using echo &...
- 91
0
votes
1
answer
29
views
Unable to get multicharacter field in fzf preview
_select () {
apt-cache search '' | fzf \
--prompt='search: '\
--marker="M" \
--ansi \
--layout=reverse \
--cycle \
--multi \
--inline-info \
--preview "...
- 97
0
votes
1
answer
97
views
Why is /dev/null needed to run asynchronous jobs in busybox sh?
I'm curious why this special device is needed to fork the command and run it asynchronously in the minimal Busybox shell.
BusyBox v1.30.1 (Debian 1:1.30.1-4) built-in shell (ash)
Enter 'help' for a ...
- 17
0
votes
2
answers
48
views
bash "catch block" is not catching bad subshell
So I have this:
(
set -eo pipefail;
{
set -eo pipefail;
file_path="$(echo "$i" | jq -r '.file_path')"
if [[ -n "$file_path" ...
- 8,992
0
votes
2
answers
47
views
Bash use arguments returned from subshell in current shell
Sorry if the title is bad (it is already the best one I can think of).
Anyway, here is the line of code:
printf "%s\n" "$(echo a b "c d")
Simple code. Of course, I will ...
- 55
0
votes
1
answer
225
views
Bash, grep - why is a command with a caret not working in a subshell?
I'm trying to determine if a git add action has created any expected modifications, and the following works in an interactive shell
$ BASE_DIR=foo/bar/baz
$ git add "${BASE_DIR}"
$ git ...
- 229
1
vote
1
answer
63
views
Why do I need to disable=SC2031
Can you tell me, why I have to # shellcheck disable=SC2030 in the following script?
get_names_and_hosts(){
unset LOCAL_HOSTS
declare -a LOCAL_HOSTS
unset LOCAL_NAMES
declare -a LOCAL_NAMES
...
- 143
0
votes
2
answers
69
views
How to design reusable script handling temporary files lifecycle for other scripts
I need to create a reusable ("utility") script handling entire set of operations with temporary files for any of my other ("application") scripts:
creation
tracking of temporaries ...
- 63
1
vote
4
answers
120
views
How to use a value from sub shell in parent shell
I'm not used to linux scripting and this is the first time I'm working on it so I'm struggling with the following problem:
Code:
while [ $pct -gt 80 ]; do
flag=1;
ls -tr | while read file; do
...
10
votes
1
answer
884
views
Different behaviour of subshells and && in bash vs zsh
My understanding of running commands in subshells is that the current shell is forked, and the subshell then does a further fork and exec on the desired commands.
I see strange behaviour when running ...
- 101
1
vote
0
answers
19
views
Queue interactive commands and attend to then in sequence
I want to have a script that adds commands to some kind of queue. I then want to run those commands interactively one at a time. More commands should be able to be added to the queue while I'm ...
- 11
0
votes
1
answer
192
views
How to pass more than one argument from `find -exec` to a `bash -c` sub-shell?
Is there a way to pass more than one argument from find -exec to a bash -c sub-shell?
Given this working invocation which searches all videos matching a glob pattern (eg "*dogs.mp4) and then ...
- 1,565
7
votes
1
answer
552
views
Why wait in this script is not executed after all subshells?
In this script, that pulls all git repositories:
#!/bin/bash
find / -type d -name .git 2>/dev/null |
while read gitFolder; do
if [[ $gitFolder == *"/Temp/"* ]]; then
...
- 499
0
votes
0
answers
33
views
How to know all subshells are executed and finished? [duplicate]
I have this script to pull all of the git repositories on my machine:
#!/bin/bash
find / -type d -name .git 2>&- |
while read gitFolder; do
if [[ $gitFolder == *"/Temp/"* ]]; ...
- 499
1
vote
1
answer
101
views
Subshell (subprocess/child process) with its own $BASHPID not listed by `ps`
I don't understand the following:
mkfifo p;
$ (>p ps -f | >>p echo $BASHPID) &
[1] 983527
$ cat p
983529
PID PPID C STIME TTY TIME CMD
981815 165343 0 19:57 pts/27 00:...
- 260
0
votes
2
answers
376
views
Example of subshell without child-shell process
I just recently learned that "subshell" is not the same as "child shell process" (see for example What is the exact difference between a "subshell" and a "child ...
- 260
1
vote
1
answer
417
views
Setting a trap for INT doesn't work in a subshell
$ bash -c "trap \"echo INT\" INT; sleep 3" & pid=$!; sleep 1; kill -INT $pid; wait
[1] 27811
INT
[1]+ Done bash -c "trap \"echo INT\" INT; ...
- 3,093
0
votes
2
answers
565
views
bash: assign to variable using a subshell, but exit main script if assignment fails
I'd like to have a bash script that has allows me to call a function to see if some data is contained in a file, and if it isn't fail the main script, kind of like the following, which is simplified ...
- 1,569
2
votes
2
answers
556
views
Capture stdout of a crashing program and shell's "segfault error" message
I have a compiled program main.bin that is supposed to print:
hello world
another line
This program generates a segmentation fault right after printing the first line.
If I run it in the shell (zsh), ...
- 333
1
vote
1
answer
354
views
Killing `sleep` in a subshell
In bash, I'm observing that calling kill on a sleeping process won't kill it if I start out with a subshell. Can you help me understand why?
function foo () {
# Start a loop with `sleep` in the ...
- 367
0
votes
1
answer
770
views
Parenthesis and curly brackets not working as expected in cron
I have set the following crontab for the root user:
root@curie:/usr/home/username # crontab -l
# /etc/crontab - root's crontab for FreeBSD
#
# $FreeBSD: release/10.0.0/en_US.ISO8859-1/books/handbook/...
- 11
0
votes
2
answers
481
views
Difference between $0 and $SHELL?
I am currently playing CTF in OverTheWire website . I was stuck on 32nd Level [ https://overthewire.org/wargames/bandit/bandit33.html ] to get password for next Level . Command to access Level 32 - ...
- 9
1
vote
1
answer
290
views
zsh: Halt when command not found
I want to stop the zsh script running when it encounters a command not found error.
I know of command_not_found_handler, but this function only allows me to print a message, not halt the parent shell.
...
- 1,413
0
votes
2
answers
311
views
How to get caller function call method in bash
Based on the following code below, is it possible to obtain the value of $caller_method from the pseudocode function below whether a function's caller has made a function call normally eg: mytest 1 or ...
- 375
0
votes
1
answer
616
views
How can a subshell return data in a variable (not file) and output distinct logs at the same time?
Say I've got the following javascript:
const something = doSomething();
function doSomething() {
console.log("About to do something");
const a = ...
1
vote
2
answers
2k
views
continue: only meaningful in a `for', `while', or `until' loop
I have a loop that checks for certain criteria for whether or not to skip to the next iteration (A). I realized that if I invoke a function (skip) that calls continue, it is as if it is called in a ...
- 561
1
vote
0
answers
151
views
How to return a value from a job?
I want to spin up some jobs within a script to do some work in parallel. I will know when the work is done by counting the number of active jobs. The issue I'm having is that I want to also return a ...
- 2,345
0
votes
0
answers
206
views
How to display banner text inside the subshell along with the results of whatever is being run in subshell
I'm trying to figure out how to display text inside a subshell along with the results of whatever is being run in the subshell, i.e: test=$(sudo echo foo)
I've already set up a lecture_file so that a ...
0
votes
2
answers
168
views
Check if the script was already run in the current shell session
I have a script that's interactive if started without arguments, and I'd like it to print an ASCII-art logo the first time it's run in the current shell session. Is this possible to detect somehow?
I ...
- 219
0
votes
0
answers
538
views
Capturing output of sudo commands run over ssh (without password prompt)?
If I run this command, the output is what I expect, listing the directory /root on my server.
~ bash -c "ssh -t myserver 'sudo ls /root'"
Enter passphrase for key '/home/james/.ssh/ed25519':...
- 719
0
votes
1
answer
562
views
How are sudo permissions granted across parent/children processes?
I was having a look at how sudo grants work across parent/children processes, however, I'm confused.
If I open a terminal (emulator, in a graphic environment), and execute:
$ sudo bash -c "sudo -...
- 849
0
votes
0
answers
226
views
Does ( ) really spawns a subshell? [duplicate]
I saw this video which explains that when running a command in parentheses it actually runs the command in a subshell, which is a child process of the original shell. Running the following experiment:
...
- 312
1
vote
0
answers
41
views
How to capture the output of a Python program running in a subshell? [duplicate]
I'm trying to run a python program at startup by putting the following lines into etc/rc.local:
(cd /home/pi/CODE/weather-project/weather-station &&
python main.py) &>> log.txt &
...
- 111
2
votes
0
answers
148
views
Is the log-in shell the parent of shells in gnome terminal?
I have somehow thought that all shells that are invoked by a terminal emulator or any other way while a user is logged in are subshells of the log-in shell. Is this correct?
If it matters, I am ...
- 153
0
votes
1
answer
1k
views
Launching a program via `xdg-open` from a subshell without blocking
I've noticed that calling xdg-open from a subshell will reliably block until the launched process is closed. I suspect there may be a reason for this, but I'm not sure as to why. For example, ...
- 266
5
votes
3
answers
1k
views
Why must I put the command read into a subshell while using pipeline [duplicate]
The command df . can show us which device we are on. For example,
me@ubuntu1804:~$ df .
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdb1 61664044 8510340 49991644 15% /home
...
- 3,009
1
vote
1
answer
3k
views
How to continue running the script when a script called in the first script exited with an error code?
I am trying to write a bash script that will run a second script repeatedly until it fails and capture the stdout and stderr of that second script. I have managed to deal with most problems ...
- 13
0
votes
0
answers
259
views
Why source same script twice is exiting the shell?
I have written a bash script to create a git worktree- cr_wt
#!/bin/bash
unset CDET_ID
unset WT_DIR
source ~/.bashrc
usage()
{
echo "Usage: $0 [ -c CDET_ID ] [ -d Directory Name ]"
...
- 229
1
vote
0
answers
504
views
In bash, can I create an anonymous read-write pipe to a subshell?
I'm trying to pass a "resolution service" to a bash script as read-write file descriptor attached to another script.
So given a "service" like capitalize:
#!/usr/bin/env bash
while ...
- 242