1

I have written this script to toggle my touchpad (I will be keybinding it), but it's not working.  Why is this code not working?  And how can I accomplish this function more elegantly?

#!/bin/sh

if [ "synclient | grep TouchpadOff | grep -o -E '[0-9]+'" ]
then
        synclient TouchpadOff=0
        notify-send "Touchpad Enabled"
else
        synclient TouchpadOff=1
        notify-send "Touchpad Disabled"
fi
6

When you write

 if [ "some string or other" ]
 then

the [ operator doesn't run some string or other, it just sees a non-empty string and says that is a true value.

You want

 if [ "`synclient | grep TouchpadOff | grep -o -E '[0-9]+'`" ] 

or the more modern

if [ "$(synclient | grep TouchpadOff | grep -o -E '[0-9]+')" ]

but there is really no need to see if the command produces a string as grep produces an exit code so

if synclient | grep TouchpadOff | grep -q -E '[0-9]+'
then

should do what you want. I don't know the output format of synclient, but I would expect you could combine the two greps into one without too much effort.

  • 1
    To combine both grep: synclient | grep -oP '\s*TouchpadOff\s*=\s*\K[0-9]+' – NotAnUnixNazi Jun 29 '19 at 21:32
  • @Isaac Is this because you know the output format of synclient, or is this a guess? – icarus Jun 30 '19 at 2:41
  • 1
    I do know the output of synclient. I am not guessing. – NotAnUnixNazi Jun 30 '19 at 3:32
3

icarus gave a pretty good answer.  Your question is hard to answer because you don’t explain exactly what the script is supposed to be doing, so we are forced to reverse-engineer it (and guess what you are thinking).

icarus guessed that you are looking to see whether the output from synclient includes a line that contains “TouchpadOff” and a number.

I guess that you are assuming / expecting that the output from synclient includes a line that contains “TouchpadOff” and a number, and you are looking to see whether that number is 0.

If icarus guessed correctly, stop reading.

If I guessed correctly, we can adapt the penultimate (second-to-last) command in icarus’s answer as follows:

if [ "$(synclient | grep TouchpadOff | grep -o -E '[0-9]+')" != 0 ]

(to test whether the number is zero) and this should be fairly portable.  But there may be a couple of shorter ways:

  • If you’re using bash, you can do

    if (( "$(synclient | grep TouchpadOff | grep -o -E '[0-9]+')" ))

    using the ((expression)) syntax.  Problems with this include:

    • It’s not POSIX-compliant, and so behavior in shells other than bash will have to be looked at on a case-by-case basis.
    • If the output from the command is null, it is treated as 0.

       

  • If you know more about what the output from synclient looks like than you are showing, you can write a smarter grep.  For instance, if you’re fairly certain that the output from synclient will contain a line that contains a string that looks like TouchpadOff = number, where number is a non-negative integer with no leading zero (i.e., it might be 0, 1, or 42, but not 01, 0.5, or off), and there might or might not be space(s) before and/or after the =, then you can do

    if ! synclient | grep -q 'TouchpadOff[[:space:]]*=[[:space:]]*0'

    In some versions of grep (e.g., GNU grep), you can shorten that to

    if ! synclient | grep -q 'TouchpadOff\s*=\s*0'

    I added the ! to reverse the truth value of the command.  grep -q 'TouchpadOff…=…0' will (obviously) succeed if it finds TouchpadOff = 0 — but, if my guess is correct, you want to do the

    synclient TouchpadOff=0
    

    command if the current value is not zero.

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