Questions tagged [process-substitution]

Process substitution a form of inter-process communication that allows the input or output of a command to appear as a file (such as: `<(cmd)` or `>(cmd)`).

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Ordering output when two subshells write to stdout

I have a command of the below form input | tee >(subshell) | mainshell Both subshell and mainshell writes to stdout. So their output is not synchronised. E.g. echo "Hello\nWorld" | tee &...
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1answer
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Process substitution with Perl script

I have a Perl script which requires the following arguments: count.pl OUTPUT_FILE INPUT_FILE What I want to do is to use process substitution instead of specifying INPUT_FILE explicitly, for instance:...
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Difference between <(commands) and >(commands) in process substitution

In process substitution I can see two syntaxes: >(command_list) and <(command_list) Often I use the second syntax. But I have no idea what is exactly the difference between the two? searching ...
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bash: how to propagate errors in process substitution?

I want my shell scripts to fail whenever a command executed with them fails. Typically I do that with: set -e set -o pipefail (typically I add set -u also) The thing is that none of the above ...
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What is the portable (POSIX) way to achieve process substitution?

Some shells, like bash, support Process Substitution which is a way to present process output as a file, like this: $ diff <(sort file1) <(sort file2) However, this construct isn't POSIX and, ...
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Zenity Cancel button for GNU parallel progress bar

As GNU parallel's manual shows, you can use a zenity progress bar with parallel: seq 1000 | parallel -j30 --bar '(echo {};sleep 0.1)' \ 2> >(zenity --progress --auto-kill) | wc However, in ...
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Can i use sudo in process substitution?

I want to calculate disk space via du, but I need sudo to access some dirs: $perl -ane '$i+=($F[0] =~ s/^(\d+).*/$1/r); print "$i\n"' <(sudo du /home) which gives: [sudo] password for ...
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1answer
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Wait for Bash process substitution subshells

I pipe the same content to multiple commands with tee, redirects and process substitution subshells like this: #!/usr/bin/env bash echo 'hello' | tee \ >( sleep 3; cat /dev/stdin ) \ >( ...
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1answer
79 views

1-liner process substitution for ksh

I have this command, which works fine for bash: sh <(curl -sSl https://appi.sh/launch) (launches this interactive script) I'd like to get this 1-liner working for ksh, too. Currently, it errors ...
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4answers
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Cryptsetup: failed to attach a loop-back device

I am using cryptsetup with detached header. For that I am using the --header parameter, to specify header file. I can open my device using: cryptsetup luksOpen /dev/sdb1 sdb1 --header LUKS-HEADER ...
3
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1answer
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Why is ssh-add <(echo 'pk contents') not working?

I am getting this error: Permissions 0660 for '/dev/fd/63' are too open. It is required that your private key files are NOT accessible by others. This private key will be ignored. when I run ...
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how to keep stty sane after piping strace to vim?

this makes vim madness: $strace -o >(vim -; stty sane) file.out; stty sane I have typed stty sane in processed substitution as well as in next command but none of them did their job. Once i piped ...
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Process substitution and redirection using tee

Suppose that you redirect, in bash, the standard output of a command cmd to a file named f.out, and the standard error to f.err, using tee to preserve console printing: cmd 1> >(tee f.out) 2>...
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1answer
536 views

Script not working when passed to bash via -c

Why does this work: $ cat test.sh #!/bin/bash cat <(date|awk '{print $1}') $ ./test.sh Thu but not as a command passed to bash: $ bash -c "cat <(date|awk '{print $1}')" Thu 2 Apr 2020 12:52:...
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Environment variables are not set when redirect echo through a pipeline at a function [closed]

This command: echo '18' | source meta-cmf-raspberrypi/setup-environment Not set the environment variables as instead happened with a simply: source meta-cmf-raspberrypi/setup-environment With "18" ...
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Why doesn't the process substitution <() work with ssh -F

I have some vagrant virtual machines. To log into them I issue the vagrant ssh command. I want to log into them using regular ssh command. The vagrant ssh-config outputs the suitable config file $ ...
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1answer
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Can't run file(1) on output of file descriptor, pipe, fifo, device, etc

I want to run the file(1) command on the output of another command, but all I get is $ file -sL <(echo \#include \<stdio.h\>) /dev/fd/63: ERROR: (null) This works as expected in file-5.04 (...
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What is the difference between a heredoc and process substitution?

In this answer, it is explained how to use a heredoc to interact with interactive programs by connecting their stdin with a heredoc. https://stackoverflow.com/questions/21130757/send-commands-to-...
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1answer
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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: ...
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1answer
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Trying to run .sh script from curl

I am having trouble running a shell script. So for context, I am using bash <(curl -s -L https://test.com/detect.sh) --argument1=true When I run this command in my Ubuntu environment, it works ...
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Bash complex redirection (what does this command do)?

I recently was messing with an AWS virtual machine setup script. The documentation says to include this line: exec > >(tee /var/log/user-data.log|logger -t user-data -s 2>/dev/console) 2>&...
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How to detect an error using process substitution

This question is similar to the following link, but focused on using the command line (bash shell). Using a simple example, when doing the following command: $ cat <(date); echo $? Fri Jul 7 21:...
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1answer
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Executing commands from process substitution in xinitrc

I felt that an .xinitrc like this #!/bin/sh bash <(sed -n 'H /^exec ./{ x s/\([^\n]\+ &\n\)*exec .*// p }' /etc/X11/xinit/xinitrc) xmonad & # ... exec xterm where ...
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How to pass to ssh the key stored in a shell environment variable?

Presumably ssh tries to access the fd several times, but the fd is destroyed after it has been read the very first time: # ssh -i <(echo $KEY) user@example.com Warning: Identity file /dev/fd/11 ...
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bash: race condition with pipeline, tee and process substitution

I want to see twice being output twice, but this script will only output it once: dump() { (sleep 1; cat) > "$1" } (sleep 0; echo "twice") | tee >(dump "./a.txt") echo "$(< "a.txt")" To ...
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1answer
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paste: /dev/fd/63: No such file or directory

I'm new to Unix command. I was trying to execute the following commands in Git Bash and it directs to error message: paste: /dev/fd/63: No such file or directory # Set Up Image Lists paste <(awk "{...
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4answers
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How to emulate Process Substitution in Dash?

In bash, I can use Process Substitution and treat output of a process as if it was a file saved on disk: $ echo <(ls) /dev/fd/63 $ ls -lAhF <(ls) lr-x------ 1 root root 64 Sep 17 12:55 /dev/fd/...
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1answer
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Why does dd dislike taking input from process substitution?

Is there something about process substitution (which I think is implemented with unnamed pipes) that is incompatible with dd? For example, this fails: $ dd if=<(unzip -p raspbian.zip) of=/dev/sdb ...
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Creating temp file vs process substitution vs variable expansion?

If I am doing something like creating temporary file some process generating output > temp_file cat temp_file process substitution: cat <(some process generating output) another way : cat ...
5
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1answer
340 views

Why ssh immediately disconnects when using -F /dev/stdin syntax?

I've configured and booted default Ubuntu VM box by the following commands: vagrant init ubuntu/trusty64; vagrant up --provider virtualbox Now, for education purposes, I'd like to use the following ...
4
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2answers
982 views

Run asynchronous tasks and retrieve their exit code and output in bash

I have to run a bunch of bash commands asynchronously and as soon as one finishes, I need to perform actions according to its exit code and output. Note that I can't predict how for long any of these ...
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bash: how to pass variables to a loop within a process substitution

How do you pass variable values within a process substitution to a loop within that process substitution? I'm reading a csv file into an associative array, and while reading each line, I would like ...
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3answers
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Process substitution with tee and paste

I'm trying to pipe a command through the output of two other commands and then merge the results of the two process substitutions. An example that gets me close is: command | tee >(sed -rn 's/.*...
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1answer
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zsh: inconsistent error handling in assignments

This is zsh -f: Fereidoons-MacBook-Pro% local a=$(jaja) && echo bad zsh: command not found: jaja bad Fereidoons-MacBook-Pro% a=$(jaja) && echo bad zsh: command not found: jaja ...
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How to use diff3 with text arguments instead of file paths?

I want to use diff3 with text arguments instead of file paths. For example, diff3 some_files/mine.txt some_files/older.txt ~/Downloads/yours.txt works as expected. However, I've been trying to achieve ...
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2answers
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Process Substitution in Bash

Can someone explain to me why I don't see the output of "date" from the below command? For N number for STDIN inputs, it's printing only for last (N-1) commands? [root@RAJ-RHEL6 raj]# cat < <(...
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5answers
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Process substitution and pipe

I was wondering how to understand the following: Piping the stdout of a command into the stdin of another is a powerful technique. But, what if you need to pipe the stdout of multiple commands? ...
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0answers
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Process substitution doesn't work with diff and node

I'm trying to compare the output of my fizzbuzz.js program: for (let i = 1; i <= 100; i++) { let out = ""; if (i % 3 == 0) out += "Fizz"; if (i % 5 == 0) out += "Buzz"; if (i % 3 &&...
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cat in process substitution hangs: what is it waiting for? [duplicate]

I have this piece of code using Process Substitution. When I run it, it works fine, but it does not exit - just hangs there waiting for input. Why and how to overcome? prepro() { in=$(<...
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Why do I seem to lose data using this bash pipe construction?

I am trying to combine a few programs like so (please ignore any extra includes, this is heavy work-in-progress): pv -q -l -L 1 < input.csv | ./repeat <(nc "host" 1234) Where the source of ...
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3answers
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Can I duplicate output of a pipe?

Well, the task is simple: a part of my script has to compute both md5 and sha1 hashes. The input is a file - big file - and hashes have to be put into MD and SH variables for later output composition. ...
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1answer
147 views

Process substitution to script in order to monitor iotop

I am actively trying to get the output of the iotop for monitoring. As you know, the iotop is interactive, meaning that once started, it'll provide live updates on disk usage on the system. I'm ...
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186 views

Write stdout to a temp file using command line

Say for example we wanted to write the env from the host to Docker container, one way would be to use a temp file: env > env_file && docker run --env-file env_file image_name to avoid a ...
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process substitution with <(gunzip …) fails

The following code returns: syntax error near ( #!/bin/bash myprogram -i <(gunzip -c file.gz) -j <(gunzip -c file2.gz) It seems it doesn't like brackets. How can I make this script work? If I ...
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1answer
166 views

How to send stdin to while loop using redirection operator

Not sure if I used the right words in the title, I am trying to do this: while read line; do echo "$line" exit; done; <( echo "foo\n"; exit ) but it hangs, I don't think the while loop ...
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1answer
246 views

concurrent processing in bash using process expansion, and redirection

Apart from possible races that have to be controlled by using proper synchronisation, it's possible in bash to feed a data source concurrently into multiple pipelines and collect all their outputs ...
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2answers
333 views

process substitution for opening a list of files with an application

I wish to use process substitution to direct a list of files (produced, for example, by ls or find) to a particular application for opening/viewing. While piping such a list to xargs is suitable for a ...
4
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1answer
1k 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://...
3
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1answer
247 views

How to use bash process substitution for a sftp private key file?

With my team, we need to share a few private keys and we store them in a pass repository. So instead of extracting the key and storing it in cleartext on the filesystem, I am looking for a way to ...
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4answers
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Why does `… | sed 's/^/stdout: /'` print on empty stdin when `… > >(sed 's/^/stdout: /')` doesn't?

I'm trying to understand what causes the difference in these 2 constructs that I thought were functionally equivalent: $ ( echo foo >&2 ) 2> >(sed 's/^/stderr: /') | sed 's/^/stdout: /' ...