CODEWITHSUNDEEP
linuxbashshellawk
B. Bagry
B. Bagry

Reputation: 25

How to awk print a subtring and trim trailing and ending white space of the same subtring in bash

Hello guys I'm trying parse xinput stdout to find the right device to disable the keyboard. So this is the code that I have but it looks sloppy and I was wondering if there was a better way of doing it.

xinput -list --short | grep -E "keyboard.*slave" | awk 'NR==1{print substr($0,7,41)}' | awk '{$1=$1}1'

I do not know how long the substring needs to be so I include 41 as the index to encompass the maximum length of the potential device names. This results in a white space at the end that needs to be trimmed so I pass it through another awk pipe. I would like to know if the last 2 awk calls can be condensed into 1

Upvotes: 1

Views: 1021

Answers (2)

ilkkachu
ilkkachu

Reputation: 6527

You can use sub() to substitute the white space away, and awk can do the pattern match for you, too:

xinput -list --short | awk '
    /keyboard.*slave/ { 
        s = substr($0, 7, 41);
        sub(/ *$/, "", s);
        print s;
        exit;
   }'

That would stop after the first matching line, which I suppose you wanted, since the original only acted on the first record read by awk.

So,

$ cat keyb
mouse mouse something
keyboard slave foo
keyboard slave bar
$ awk '/keyboard.*slave/ {  s = substr($0, 7, 41); sub(/ *$/, "", s); print s; exit; }'  < keyb
rd slave foo

Upvotes: 2

George Vasiliou
George Vasiliou

Reputation: 6335

As an alternative to disable your keyboard you can use xinput directly.

The output of xinput is like this:

$ xinput list
Virtual core pointer                          id=2    [master pointer  (3)]
   ↳ Virtual core XTEST pointer               id=4    [slave  pointer  (2)]
   ↳ VirtualBox mouse integration             id=9    [slave  pointer  (2)]
   ↳ ImExPS/2 Generic Explorer Mouse          id=11   [slave  pointer  (2)]
Virtual core keyboard                         id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard             id=5    [slave  keyboard (3)]
    ↳ Power Button                            id=6    [slave  keyboard (3)]
    ↳ Sleep Button                            id=7    [slave  keyboard (3)]
    ↳ Video Bus                               id=8    [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard            id=10   [slave  keyboard (3)]

The keyboard description i.e AT Translated Set 2 keyboard is always the same. What is different is the id=10 (different id can be assigned by the system across reboots).

As a result you can get the id of your keyboard like 

$ xinput list --id-only "AT Translated Set 2 keyboard" 
10

And you can then disable your keyboard like

$ kid=$(xinput list --id-only "AT Translated Set 2 keyboard")
$ xinput disable "$kid"   #use xinput enable to enable it.

Or even you can use device description directly with xinput disable:

$ xinput disable "AT Translated Set 2 keyboard"

As a result , since device description is always the same , you don't need any kind of text processing to identify and disable your keyboard.

Upvotes: 1

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