# Shell Command to make environmental variables
**URL:** https://discourse.julialang.org/t/shell-command-to-make-environmental-variables/116997
**Category:** General Usage
**Tags:** cmd
**Created:** [July 13, 2024, 1:06pm UTC](https://discourse.julialang.org/t/shell-command-to-make-environmental-variables/116997 "2024-07-13T13:06:47Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@s-baumann](https://discourse.julialang.org/u/s-baumann)
#### Post date: [July 13, 2024, 1:06pm UTC](https://discourse.julialang.org/t/shell-command-to-make-environmental-variables/116997/1 "2024-07-13T13:06:47Z")
I am on linux and trying to execute the following in a Julia REPL:
> run(`export JULIA_NUM_THREADS=4`)
I get the error ERROR: IOError: could not spawn `export JULIA_NUM_THREADS=4`: no such file or directory (ENOENT)
I can execute simpler commands like run(`ls -l`) successfully. I just can’t make environmental variables. This is really confusing as if I copy paste this into a terminal directly it does work. So it seems like this is a bug in Julia (or it is just really complicated to execute terminal commands in Julia).
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### Author:  [@sgaure](https://discourse.julialang.org/u/sgaure)
#### Post date: [July 13, 2024, 1:14pm UTC](https://discourse.julialang.org/t/shell-command-to-make-environmental-variables/116997/2 "2024-07-13T13:14:37Z")
The julia `run` function executes programs. The shell command `export` is not a program, it’s a builtin shell command. If you want to start a shell from julia you can do it explicitly with e.g. `run(`/bin/bash -c ""`)`
> The command is never run with a shell. Instead, Julia parses the command syntax directly, appropriately interpolating variables and splitting on words as the shell would, respecting shell quoting syntax. The command is run as `julia`’s immediate child process, using `fork` and `exec` calls.
[https://docs.julialang.org/en/v1/manual/running-external-programs/](https://docs.julialang.org/en/v1/manual/running-external-programs/)
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### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [July 13, 2024, 1:20pm UTC](https://discourse.julialang.org/t/shell-command-to-make-environmental-variables/116997/3 "2024-07-13T13:20:19Z")
That being said, changing the environment variables is done by writing to the `ENV` dictionary.
Either way, changing `JULIA_NUM_THREADS` in a running session won’t increase the number of running threads. You have to set that environment variable before you start julia (that also means outside `startup.jl`).