Example:
abcd@abcd-abcde:~$ xinput --list --short
Virtual core pointer
↳ SynPS/2 Synaptics TouchPad id=11 [slave pointer (2)]
↳ Logitech USB RECEIVER id=12 [slave pointer (2)]
How would I extract a column from the output, say the second one? And, for example, store it in a variable?
Is it possible to do this?
That's exactly what awk was made for. Using the output of xinput on my system:
$ xinput --list --short
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ SIGMACHIP USB Keyboard id=12 [slave pointer (2)]
⎜ ↳ Logitech M325 id=14 [slave pointer (2)]
⎜ ↳ AlpsPS/2 ALPS DualPoint Stick id=17 [slave pointer (2)]
⎜ ↳ AlpsPS/2 ALPS DualPoint TouchPad id=16 [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)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Power Button id=8 [slave keyboard (3)]
↳ SIGMACHIP USB Keyboard id=11 [slave keyboard (3)]
↳ Dell WMI hotkeys id=18 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=13 [slave keyboard (3)]
↳ Sleep Button id=9 [slave keyboard (3)]
↳ UVC Camera (046d:0819) id=10 [slave keyboard (3)]
$ xinput --list --short | awk -F"\t" '{print $2}'
id=2
id=4
id=12
id=14
id=17
id=16
id=3
id=5
id=6
id=7
id=8
id=11
id=18
id=13
id=9
id=10
awk will automatically split each input line into fields on the value given by -F. By default, it splits on whitespace, but here we need a tab. The 1st field is $1, the second $2 etc.
Alternatively, you can use cut:
$ xinput --list --short | cut -f2
id=2
id=4
id=12
id=14
id=17
id=16
id=3
id=5
id=6
id=7
id=8
id=11
id=18
id=13
id=9
id=10
You can save the output in a shell variable just like you would for any other command:
$ ids=$(xinput --list --short | awk -F"\t" '{print $2}')
$ echo $ids
id=2 id=4 id=12 id=14 id=17 id=16 id=3 id=5 id=6 id=7 id=8 id=11 id=18 id=13 id=9 id=10
$ echo "$ids"
id=2
id=4
id=12
id=14
id=17
id=16
id=3
id=5
id=6
id=7
id=8
id=11
id=18
id=13
id=9
id=10
You could also save it as an array:
$ ids=( $(xinput --list --short | awk -F"\t" '{print $2}') )
$ echo ${ids[@]}
id=2 id=4 id=12 id=14 id=17 id=16 id=3 id=5 id=6 id=7 id=8 id=11 id=18 id=13 id=9 id=10
$ echo ${ids[2]}
id=12
\t, tab. Anything up to the 1st tab will be considered the first field, so yes, the arrows will be included.
Knowing that the items are tab separated, we can use shell-only way with $IFS variable and while read ; do . . .done structure.
$ xinput | while IFS=$'\t' read ONE TWO THRE ; do
> echo $TWO
> done
id=2
id=4
id=11
id=3
id=5
id=6
id=7
id=8
id=9
id=10
id=12
To store items in a variable, we can use arrays, and
$ xinput | { while IFS=$'\t' read ONE TWO THRE ; do
> array+=( "$TWO" )
> done ;
> echo ${array[@]}
> }
id=2 id=4 id=11 id=3 id=5 id=6 id=7 id=8 id=9 id=10 id=12
Notice me using command | { command1 ; command2 ; command3 } structure. You will quickly learn that pipes start subshells and variables in subshells don't affect the main shell , thus you have to come up with some way of preserving those variables.
As for extracting a row , well that's fairly easy with grep:
$ xinput | grep 'Virtual core keyboard'
⎣ Virtual core keyboard id=3 [master keyboard (2)] # extract line with specific string
↳ Toshiba input device id=12 [slave keyboard (3)]
$ xinput | sed -n '3p' # extract 3rd line
⎜ ↳ SynPS/2 Synaptics TouchPad id=11 [slave pointer (2)]
$ in front, hence using printf
May 6, 2016 at 14:05
to extract the column you could try awk
% xinput --list --short | awk '{print $3}'
core
Virtual
SynPS/2
core
core
Button
Bus
...
to assign that output to a variable a. note the value of this variable will be a string containing newlines after each word - not the easiest to work with. Probably better to assign to an array.
% a=$(xinput --list --short | awk '{print $3}')
vel@ubuntu:/media/michael/3ae9487f-1652-400e-8136-fe63519941ed% echo $a
core
Virtual
SynPS/2
core
core
Button
Bus
Button
USB2.0
WMI
Translated
awk -F"\t" {print $2}.