Questions tagged [subshell]
The subshell tag has no usage guidance.
165
questions
1
vote
1answer
26 views
What is the difference between executing in subshells vs using & vs coproc command?
I was recently reading about subshells in linux. An example used was sleep 10.
(sleep 10) - subshell
sleep 10& - background process
coproc sleep 10
It was written that the first command ...
3
votes
1answer
30 views
Can I determine if the current function has been invoked via command substitution?
foo() {
if [[ something ]]; then
echo "The foo function was called directly."
else
echo "The foo function was invoked via command substitution."
fi
}
Call foo ...
0
votes
2answers
24 views
$! is empty when running command in bash with -c or in subshell
I am trying to get the pid of the previous command with $!, but that only works in the 'main' shell:
$ echo "test" | echo $!
4436
$
If I start a subshell, then it's empty:
$ bash
$ echo &...
1
vote
2answers
104 views
less stops my script; why is that and how to avoid?
I have this Bash script named as s in current directory:
#!/bin/bash
pipe_test() {
( set -m; (
$1
); set +m ) |
(
$2
)
}
pipe_test "$1" "$2"
If I call e.g.
./s yes ...
1
vote
1answer
77 views
Differences between (command) and command in bash
While investigating the problem of redirecting the stderr of the bash keyword time and the standard solution to the problem, I came across another question.
The description man bash gives of the (list)...
0
votes
1answer
74 views
Why does Bash run scripts in subshells?
Why does the Bash shell run scripts in subshells? What is the advantage of doing so?
0
votes
0answers
25 views
How a command which is meant to output indefinitely, when piped to another command that waits for a certain amount of input, knows when to terminate?
I am baffled by how piping in bash works.
Take a random string generator, for example:
tr -dc 'A-Z0-9' </dev/urandom
spawned tr process that reads from /dev/urandom indefinitely, as far as /dev/...
0
votes
0answers
43 views
Variable losing value [duplicate]
Anyone have suggestions? Thanks in advance.
#!/usr/bin/env bash
VAR=$(
ssh -q -T -o ConnectTimeout=10 server01 " df -Ph" ; EXITSTATUS="$?" | sed -r '/^\s*$/d' | grep -v "test" | wc -l
)
echo $...
1
vote
1answer
22 views
Different behavior of progress bars: local vs. remote ssh bash script
I am having issues to get minimal progress bars working in local scripts which are executed remotely via ssh. Depending on the command I get other undesired progress indicators (lines of dots with ...
0
votes
1answer
64 views
How to pass a subprocess to a command with bash
I'm trying to pass multiple outputs to a command using sub-processes.
This is (a shortened version of) my command:
cat "$1"
one=cat "$1"
The output of command <(echo "foo") is
foo
/dev/fd/63: ...
0
votes
1answer
40 views
How to exit the parent script as failed when the child script fails
I have a script which calls another script.
Now even if the second script fails it's still succeeding original script.
Below is the first part of the script:
#OBJ_TYP=`echo $Job_detail_corr | awk -...
4
votes
1answer
157 views
Why is $! returning the wrong process ID for a subshell running in background?
$(sleep 5) &
echo $!
sleep 1
echo "done"
The above outputs:
$ ./test.sh
7483
done
However if I search for sleep in ps aux I see:
ps aux | rg sleep
chris 7484 0.0 0.0 132788 1432 pts/6 ...
0
votes
2answers
99 views
Why grep --include with curly braces fail in subshell? [duplicate]
This works in shell:
grep -R --exclude-dir=storage --exclude-dir=node-modules --include=*.{scss,css} loader.gif
But this fails:
sh -c "grep -R --exclude-dir=storage --exclude-dir=node-modules --...
1
vote
2answers
117 views
Does shell maths run in a subshell?
When I perform a simple math operation in #!/bin/sh, does that create a subshell?
E.g.,
addition=$(( 1 + 1 ))
The syntax would suggest a subshell, but I couldn't find anything on this
4
votes
1answer
195 views
In bash, how can I retrieve the exit code of a subshell when using local
This question is close to others - Can I get the exit code from a sub shell launched with $(command)?
However there are no solutions I've found that allows me to get an exit code from a sub shell ...
0
votes
0answers
142 views
Bash completion not working in subshell
If I open a terminal window, or open a terminal in tmux, tab completion works as expected, but if I type bash to open a subshell, it doesn't. Below is my .bash_profile and .bashrc
# .bash_profile
[[ ...
0
votes
1answer
103 views
Are subshells run in parallel by default?
This question follows from this one and one of its answers' recommendation to read Linuxtopia - Chapter 20. Subshells.
I'm a bit confused by this statement at the Linuxtopia site:
subshells let ...
0
votes
0answers
55 views
How can I get exit status of subshell?
A classical example of piping:
$ false | true
$ echo ${PIPESTATUS[@]}
1 0
Same example run in a subshell and assigning results into a variable:
$ process="$(false | true)"
$ echo ${PIPESTATUS[@]}
0
...
0
votes
0answers
65 views
Terminate a subshell background process
I am starting entr as a subshelled background process as described in its man page to listen to changes to some file foo, occuring during interactive use of some program baz, and I would like to ...
10
votes
2answers
772 views
How to print and use a command output in a one-liner?
I'd like to pass the result of mktemp as argument to a command, let's say gcc -o. gcc -o $(mktemp) causes the result to be used, but I need to figure out the result.
The only thing I could come up ...
3
votes
1answer
152 views
Nested command substitution does not stop a script on a failure even if -e and shopt -s inherit_errexit are set
Suppose you have a following script sandbox.sh.
(This looks similar to Command substitution inside a function does not stop the script on a failure even if -e is set, but I believe a bit different ...
1
vote
0answers
35 views
How can I create a function that memoizes other commands?
I have created the following function to memoize any command:
# zsh
(( $+functions[ec] )) || {
ec() print -r -- "$@"
ecerr() { ec "$@" 1>&2 }
ecdbg() ecerr "$@"
gq() { ec "${(q+...
0
votes
0answers
26 views
Shell: Open REPL in function
I want to open an interactive REPL in my zsh functions (mainly for debugging purposes); Exactly like IPython.embed().
One way to do something similar is to simply invoke another instance of zsh, but ...
0
votes
1answer
54 views
Subshell Job Clarification
I run the command (Xorg & sleep 3; xeyes) & to test Xorg, and group it into a single subshell background job to make management easy. This works properly, and opens xeyes in the new Xorg ...
1
vote
1answer
115 views
Can you explain this inner working of this printf command in bash?
I stumbled onto the question Replacing only specific variables with envsubst and in one of the comments was this shell example:
envsubst "$(printf '${%s} ' ${!PREFIX*})" < infile
See the original ...
4
votes
0answers
107 views
Is job-control really meant to be supported in subshells and scripts?
Small premise
I use subshells quite often to perform operations that involve changing the Shell Execution Environment, so as not to affect the main shell. I do it often from an interactive shell, and ...
0
votes
2answers
156 views
Set shell variable then invoke subprocess fails
I was playing with getopts, which has a shell variable OPTERR that influences its behavior. I wanted to change the value of OPTERR and invoke getopts on the same line, to affect the behavior of ...
5
votes
2answers
98 views
How to handle async subshell exit
Say I have this:
set -e;
(
docker stop notifier-server
docker rm -f notifier-server
exit 1 # explicitly exit with non-zero
) &
wait;
echo 'we are here now'
will we always get to ...
0
votes
2answers
78 views
Precedence of subshells in relation to redirection?
Shell: GNU BASH
I've been using the following command for a while now:
echo "$(fmt -w 50 < foo.txt)" > foo.txt
Without any issues. However, when I try:
fmt -w 50 < foo.txt > foo.txt
...
10
votes
2answers
589 views
Why does a brace command group need spaces after the opening brace in POSIX Shell Grammar?
TL;DR: Why does POSIX brace group need spaces after { reserved word but subshell doesn't after reserved word (?
POSIX shell grammar defines brace group and subshell as follows
brace_group : ...
28
votes
3answers
5k views
How can I detect if I'm in a subshell?
I'm trying to write a function to replace the functionality of the exit builtin to prevent myself from exiting the terminal.
I have attempted to use the SHLVL environment variable but it doesn't seem ...
0
votes
0answers
58 views
Run script in background using `&` or `()&`?
If I want to run a script in background, for example a.sh, should I run
./a.sh &
or should I put it in a subshell then background it?
(./a.sh) &
I test both and don't see difference, both ...
2
votes
1answer
238 views
Bash script to count number of executions instances does not work
I am writing a script that detects if there is any instance of it already running on my Linux machine and shows on screen the number of instances.
The content of the "detect_itself.sh" script is:
#!/...
1
vote
1answer
56 views
Is it possible for sendmail to not use all the output from a bash subshell piped to it?
( GNU bash, version 4.2.50(1)-release (powerpc-ibm-aix6.1.2.0))
(
echo "a"
echo "b"
echo "c"
)| sendmail -F "Sender" recipients@a.com
This runs inside a .sh file, and the log (when ran with the -x ...
-2
votes
2answers
43 views
Identifying shell script's subshell number from within a script itself
I am accidentally caught in a desire to reveal the subshell number (BASH_SUBSHELL) from within the script itself, but i get subshell 0
Here is the script's line
echo "Operated from subshell: $...
0
votes
1answer
96 views
Exported Date Variable not appearing in subshell
I'm currently working on creating 2 bashes with two different scripts which result in two files named with the same timestamp for easy comparison/processing later. The date variable gets created in ...
1
vote
1answer
192 views
Terminating infinite-loop script embedded in tmux status bar
I have an infinite while loop bash script embedded in tmux status bar. In ~/.tmux/conf:
set -g status-right '... #(path/loop.sh) ...'
Tmux seems to run this script with sh -c. After tmux started:
$ ...
4
votes
1answer
921 views
Process substitution inside a subshell to set a variable
I'm trying to run a script remotely and use its standard output to populate a variable. I'm doing this to avoid temporary files.
Here's the pattern I'm trying:
var=$(bash <(curl -fsSkL http://...
23
votes
3answers
3k views
How does this script ensure that only one instance of itself is running?
On 19 Aug 2013, Randal L. Schwartz posted this shell script, which was intended to ensure, on Linux, "that only one instance of [the] script is running, without race conditions or having to clean up ...
0
votes
1answer
141 views
How can I stop a child process of a subshell (as per SIGSTOP) before the subshell exits?
In bash, when running ( sleep 123 &), the sleep 123 process will continue running, when the subshell exits. How can I stop the sleep 123 process before its parent subshell exits?
I'm trying to ...
0
votes
1answer
70 views
Confused why script does not exit
I have this script verbatim:
#!/usr/bin/env bash
handle_json(){
while read line; do
cat <<EOF
{"@json-stdio":true,"value":{"mark":"$1","v":"$line"}}
EOF
done;
}
( echo; echo; echo '...
13
votes
2answers
5k views
How can I get the pid of a subshell?
How can I get the pid of a subshell?
For example:
$ echo $$
16808
This doesn't work, because the original shell expands $$:
$ ( echo $$ )
16808
Why does single quoting not work? After the ...
0
votes
2answers
91 views
“Globally Store” PID of file started from bash script
I'm compiling a latex file in a script and then I'm trying to either open a new pdf reader window or reload the current one (llpp being my reader), so after compiling my script does
pdflatex $...
7
votes
1answer
1k views
exit not terminating the script [duplicate]
exit doesn't terminate the script when error is called..
output
Error: Could not resolve localhost
after exit
script
#!/bin/sh
resolve_ip (){
if [ -z "$1" ]; then
host="localhost"
...
1
vote
1answer
322 views
Weird behavior in zsh random generator
I have this script to generate $1 digit(s) of mixed random char from the defined charlists as arrays.
#!/bin/bash
charlist1=(a b c d e f g h i j k l m n o p q r s t u v w x y z)
charlist2=(0 1 2 3 4 ...
0
votes
1answer
103 views
Catch result of sub-process in Z-shell
AAA <options>; CCC AAA <options>
AAA, CCC are different commands.
Here we're in an zsh script - for example:
vi script.zsh
<...>
AAA <options>; CCC AAA <options>
<.....
2
votes
1answer
1k views
VNC clipboard not working
If I uncomment the two lines in my ~/.vnc/xstartup that enable 'normal' desktop environment for VNC, the vncconfig -iconic & command is ignored:
#!/bin/sh
# Uncomment the following two lines for ...
2
votes
0answers
58 views
How to make a script being called inside another script in a ssh command? [closed]
I have a ssh calling a script in a server, named /opt/scripts/script1.sh.
sshpass -p 'password' ssh user@ip /opt/scripts/script1.sh
(I know sshpass is not secure but there's a reason for that in ...
asked Aug 22 '18 at 7:09
Somebody still uses you MS-DOS
3,9057 gold badges28 silver badges41 bronze badges
1
vote
1answer
140 views
Export vars env to tmux's window/session/pane's env
Is there any way to export/upgrade list of variable env from a file or something to tmux's window/session/pane?
Here I have to manually source .bashrc to update new var env to each tmux's pane.
0
votes
1answer
343 views
Run bash subshell with commands as other user and not return to parent shell
As part of my quest to preserve bashrc and vimrc when switching to non-root users, I plan on making some super ugly aliases to switch to other users, immediately execute some commands, and then drop ...
