Capture output of a command, process it and ONLY then output to terminal

Question

I would like to capture the stdout (as sent to a terminal), and perform some processing after it is output on the terminal (for the user).

I want to know how to grab the output, process and make changes accordingly.

(If possible) I want this to happen for every command I type on the terminal.

---

Edit: After a dialogue in a temporary chat forum it was clear that

• we should

  • both look for which commands are issued
  • and what output there is from the commands and

• do something, if a particular command or output is detected.

Answer 1

Well, maybe it is not a good idea to grab the output, process and display the output of every command you type on the terminal.

But you can do it for some particular command via tee

your-command | tee saved-output | processing-tool

When you have seen the result from the processing-tool, you can look at the saved-output for example with cat (if short output) or less (if long output).

Example:

$ LANG=C sudo lshw | tee saved-output | grep -i -A2 disk
        *-disk              
             description: ATA Disk
             product: KINGSTON SKC300S
             physical id: 0.0.0
--
        *-disk
             description: ATA Disk
             product: WDC WD4002FYYZ-0
             vendor: Western Digital
$ less saved-output

---

After a dialogue in a temporary chat forum , I suggest to

• try vialog or viafifo according to the following links
• maybe modify one of them to do what is expected in this case,
  • both look for which commands are issued
  • and what output there is from the commands and

• do something, if a particular command or output is detected.

• Send a notification or alert when bash asks for input from user

• This link to AskUbuntu

It works directly to use vialog like the following example.

vialog 2>&1 | tee saved-output | grep 'docker container ls' && echo 'it was mentioned'

In the real case, I think you would like to start something more advanced than echo 'it was mentioned', but this is only a demo example. And things can be more efficient, if you build the specific checks into vialog and disable the alerts, that are probably not necessary in your case.

Screenshot during the dialogue:

Screenshot after the dialogue:

This way you can easily check if a command that is called is not found:

$ LANGUAGE=C vialog 2>&1 | tee saved-output | grep -i 'Command.*not found' && echo 'it was mentioned'
Command 'docker' not found, but can be installed with:
it was mentioned
$ cat saved-output 
----- start vialog at 2019-01-12 18:57:33 ----------------------------
$ docker container ls

Command 'docker' not found, but can be installed with:

sudo apt install docker.io

$ exit
exit
------- end vialog at 2019-01-12 18:58:01 --- used 28 seconds