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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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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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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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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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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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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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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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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56 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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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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165 views

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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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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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://...
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1answer
56 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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Why is the stdout of a `>()` subshell different if it's part of a redirection (e.g. `> >()`)?

This is a followup question to: Why does `... | sed 's/^/stdout: /'` print on empty stdin when `... > >(sed 's/^/stdout: /')` doesn't? To be more concrete, why is this a ...
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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: /' ...
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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 '...
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Is this bash argument substitution?

While studying bash process substitution, I found this: counter=0 while IFS= read -rN1 _; do ((counter++)) done < <(find /etc -printf ' ') echo "$counter files" If I understand correctly,...
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Does process substitution need to be double quoted?

Double quoting command substitution is a good practice. Is it the same for process substitution (<() and >())? It seems double quotes allow command substitution, but disallow process ...
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Using a here-doc with trailing backslashes inside a process substitution in bash

This: cat <<EOF one two three EOF Prints: one two three And this: cat <<EOF one \\ two \\ three EOF Prints: one \ two \ three But while this: cat <( cat <<EOF one two ...
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1answer
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Specifying the file extension produced by zsh process substitution

I want to use zsh's process substitution to create a temporary file that can then be read by another program. However, the file it generates has no file extension, so the program reading it refuses to ...
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Pass input to multiple commands and compare their outputs

I am trying to pass standard input into multiple commands and compare their outputs. My current attempt seems close, but doesn't quite work - plus it relies on temporary files which I feel would not ...
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Command requires file, avoid creating temporary file [duplicate]

<() doesn't seem to do what I expect. This command requires a text file (it's JLinkExe, the text file contains commands for JLinkExe to run. But that shouldn't matter). JLinkExe -CommanderScript &...
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Process substitution of commands on separate lines of a string

I have a variable, COMMANDS, that contains a list of newline-separated commands (I know for example in this case that there will never be newlines, but they could be separated by NUL). For example, ...
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simple cat echo process substitution hangs

Simple process substitution with cat seems to hang: cat >( echo hello; ) never finishes. Also tried: cat >( echo hello; exit; ) Manually closing the standard out file descript from the ...
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1answer
399 views

multiple pipes in loop, saving pipeline-result to array

I am trying to do the following (using bash): Search for files that always have the same name and extract data from these files. I want to store the extracted data in new arrays I am almost there, I ...
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59 views

How to create sh compatible bash function

I have this bash function: zmx(){ "$@" \ 2> >( while read line; do echo -e "r2g: $line"; done ) \ 1> >( while read line; do echo -e "r2g: $line"; done ) } this function is ...
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Which signal >(process) receives after main shell exits?

This is a Zshell question, although Bash, if it has >(command) syntax (i.e. process substitution of such kind), can hint a solution too. This really basic code explains all: % fun() { setopt ...
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222 views

Using process substitution, only send stderr to process

I have this: exec > >( while read line; do echo " stdout: $line"; done ) exec 2> >( while read line; do echo " stderr: $line"; done ) echo "rolo" >&2 echo "cholo" if you run that ...
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362 views

Why process substitution is faster than pipe in this case? [duplicate]

I am wondering why ls -1 | while read file; do echo $file; tail -n 100 $file > >(sleep 1 && cat > $file) done is faster than ls -1 | while read file; do echo $...
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Process substitution vs FIFO (created by `makefifo`)

As far as I know, process substitution in bash and FIFO (created by mkfifo) are both named pipes. They both seem viable solutions for communication between processes. I was wondering how to decide ...
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When does a command in a process substitution or FIFO start and finish running?

When does a command in a process substitution in bash start and finish running? E.g. when does command1 in command2 >(command1) start and finish running respectively? when does command3 in ...
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GPG error: “do_plaintext: wrote X bytes but expected Y bytes”

I'm having trouble using gpg when I use the <() syntax for process substitution. Here is a minimal-working example of my problem: $ gpg2 -c -o out.gpg <(head -c 73729 /dev/zero) gpg: ...
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Conditional process substitution

I have a command with a number of arguments: my_command --arg1 <arg1> \ --arg2 <arg2> \ --arg3 <arg3> I've wrapped the invocation of my_command in a function that sets up ...
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1answer
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Misunderstanding the purpose of a process substitution

I guess I'm missing some understanding on the use cases of a process substitution. My intuition was that a process substitution, of the form <(COMMANDS) would execute COMMANDS and then feed the ...
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non-deterministic output from independent processes run concurrently by process substitution

On bash v4.1.2(2), the following simple statement, chosen merely as a minimal example demonstrating the problem, gives seemingly random output: $ for n in {0..1000}; do echo "$n"; done | tee >(...
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Bash Process Substitution Hangs When Listing Bindings

TLDR: cat <(INPUTRC=/dev/null bash -c 'bind -pm emacs') # freezes # I can't use this because I need to pipe the output of the bind cat <(INPUTRC=/dev/null bash -c 'bind -pm emacs' &) # ...
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344 views

Iteratively write to the same process substitution file on MacOs

The following bash-fu code works fine on Linux but breaks on MacOS: files="foo bar" echo PROG 1 for file in $files do echo $file | tee -a tempfile.txt done sort -u tempfile.txt echo PROG 2 ...
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`tee` and `bash` process substitution order

I'd have supposed this code would have printed "oof" first: echo foo | tee >(rev) | ( sleep 1 ; cat ; ) Output: foo oof Increasing the sleep time doesn't change the order. Why doesn't that ...
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471 views

Bash - process substitution in chroot without /dev and /proc

I have a chroot jail without /dev and /proc mounted. When I try to do process substitution here, this happens: bash-4.4# cat <(ls) cat: open /dev/fd/63: No such file or directory I tried to ...
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920 views

The process substitution output is out of the order

The echo one; echo two > >(cat); echo three; command gives unexpected output. I read this: How process substitution is implemented in bash? and many other articles about process ...
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1answer
907 views

Difference between subshells and process substitution

In bash, I want to assign my current working directory to a variable. Using a subshell, I can do this. var=$(pwd) echo $var /home/user.name If I use process substitution like so: var=<(pwd) ...
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bash wait for process in process substitution even if command is invalid [duplicate]

I'm trying to write a utility script errpipe with a simple api that runs stderr through a filter. At first I tried to implement it using bash's process substitution feature. #!/bin/bash com="$1" ...
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Difference between 'cmd1 | cmd2' and 'cmd2 <(cmd1)' and 'mkfifo foo; cmd1>foo; cmd2 foo'?

Or: When and why to not prefer STDIN when cmd2 can use both, and is a single command? I come across questions on this site, where 3 of their answers are one of each of the above, like this one. This ...
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bash timeout command kills randomly before duration

I'm trying to show thumbnails from youtube for specific timeout to user and then show next one I made this command: while read line; do\ wget -O- -q "$line" | \ timeout 10s display ;\ ...
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1answer
56 views

Equivalence to the usage of process substitution?

Is the usage of process substitution command1 <(command2) equivalent to command2 > ~/myfile command1 ~myfile ? Can the two above be replaced with each other? Does command1 and command2 ...
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Sensitive data in process substitution

Let's say I do: #!/bin/bash #content=$(cat -) content="foo" pass=$1 echo $content | ccrypt -f -k <(echo -n $pass) Can the permission set on the process substition /dev/fd/* files be trusted to ...
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How to execute an output string without bash's command substitution?

How to execute an output string without bash's command substitution? For example, if I type in terminal tshark, and the program isn't installed yet, I will recieve an error message like: _some text_ ...