This is a text-only version of the following page on https://raymii.org:
---
Title : Send commands or input to a detached screen session
Author : Remy van Elst
Date : 02-10-2019
URL : https://raymii.org/s/snippets/Sending_commands_or_input_to_a_screen_session.html
Format : Markdown/HTML
---
This snippet will show you how to send commands to a running screen session.
This includes actual shell commands or keyboard input, as well as screen
commands, for example to set a logfile.
As I'm writing this article, I notice that [today screen 4.7.0 is released][3].
<p class="ad"> <b>Recently I removed all Google Ads from this site due to their invasive tracking, as well as Google Analytics. Please, if you found this content useful, consider a small donation using any of the options below:</b><br><br> <a href="https://leafnode.nl">I'm developing an open source monitoring app called Leaf Node Monitoring, for windows, linux & android. Go check it out!</a><br><br> <a href="https://github.com/sponsors/RaymiiOrg/">Consider sponsoring me on Github. It means the world to me if you show your appreciation and you'll help pay the server costs.</a><br><br> <a href="https://www.digitalocean.com/?refcode=7435ae6b8212">You can also sponsor me by getting a Digital Ocean VPS. With this referral link you'll get $100 credit for 60 days. </a><br><br> </p>
### screen commands vs shell commands (input)
For my [recent article][1] on serial port data I figured out how to send a command
to a running but detached screen session. This was a screen command, not a shell command.
screen commands are the same things as what you would put in a `.screenrc`
file or inside a screen session via `CTRL+A :`. For example, the command
logfile filename.txt
tells screen to log the output to a text file named `filename.txt`.
Shell commands are things you type in your terminal. Both commands like `ls`
or keyboard shortcuts like `CTRL+C`.
You can start a detached screen session with the following command:
screen -dmS sessionName [command-to-run]
With the command
screen -ls
you can view all screen sessions and with either `screen -r` or `screen -x` you
can reattach to a session.
### Sending commands to screen
As explained above, there is a difference between shell commands and screen commands.
screen has the `-X` flag which allows you to send a (screen) command to a session.
To send a screen command to a session:
screen -S sessionName -p 0 -X screen command
The `-p 0` flag is for the window inside screen. If you have created multiple
windows (`CTRL+A c`) you can specify the number. With `CTRL+A [0-9]` you can
directly go to that window inside screen.
For screen commands, after the `-X` flag you don't need quotes. So for the logfile
command:
screen -S sessionName -p 0 -X logfile filename.txt
For shell commands or keyboard input, we need to use the screen command `stuff`.
If you have a running screen session and you want to send the `ls` command:
screen -S sessionName -p 0 -X stuff "ls^M"
After the `stuff` you do need quotes. The `^M` is the keycode the `ENTER` key
sends to the terminal. If you omit it, screen will just type `ls` onto your terminal
but not send the `ENTER` key afterwards.
To send a `CTRL+C` to a session (e.g. to stop a running interactive process):
screen -S sessionName -p 0 -X stuff "^C"
If you need to find out what keycode a specific key sends, in bash you can
press `CTRL+V` and then the special key. The `PGDOWN` key for example:
^[[6~
More documentation on the `stuff` command [can be found here][2].
[1]: /s/blog/Get_serial_port_data_on_the_web_with_live_updating.html
[2]: https://www.gnu.org/software/screen/manual/html_node/Paste.html#Paste
[3]: https://lists.gnu.org/archive/html/screen-users/2019-10/msg00000.html
---
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