How filter text in shell interactively ("on fly")?

Question

windows 10, Emacs 26.1

M-x shell

I start Android application that very long time generate many lines in shell.

adb logcat -vtime

Here example:

In all of this text I need only lines that contain this text:

com.example.myprojectname

I need to filter this "on fly" interactively. It's very important. So the result must be.

1. M-x shell
2. Start my Android app
3. On shell show ONLY lines that contains text com.example.myprojectname
4. This MUST be happen "on fly" interactively

Is it possible?

Answer 1

If you don't have a grep available, you can use comint-preoutput-filter-functions to do the filtering for you. You need to arrange for that variable to have the right value in shell-mode, which can be done using add-hook. Since shell-mode adds its own functions to that variable already, you need to perform the addition in the shell-mode hook function. Something like the following, which assumes your prompt starts with $ or ~

(defun my-comint-filter (str)
  (if (string-match "^\\$\\|^\\~\\|com\\.example\\.myprojectname" str)
      str
    ""))
(defun my-shell-mode-hook ()
    (add-hook 'comint-preoutput-filter-functions 'my-comint-filter t t))
(add-hook 'shell-mode-hook 'my-shell-mode-hook)

Answer 2

can you do the plain unix pipe trick of:

1. M-x shell
2. myAndroidApp | grep --line-buffered -i com.example.myprojectname

that is what I do. Or are there special requirements?

as others have mentioned. The text after the grep command is a regular expression (the -i is a flag for case insensitive matching). To get the pattern to match you may need to escape characters. The escape mechanisms for bash (unix, linux, Mac etc) are different from MS Windows. The escapes for Window's CMD are here: https://ss64.com/nt/syntax-esc.html. If you search for how to use grep, most of the examples will be for unix's bash. Just a heads up.