I'm trying to add a function to the .bashrc file.

The function is supposed to change any Application window's opacity according to the command line argument.

opa(){ sh -c 'xprop -f _NET_WM_WINDOW_OPACITY 32c -set _NET_WM_WINDOW_OPACITY $(printf 0x%x $((0xffffffff * $1 / 100)))'
}

I tried the above however it throws this error:

sh: 1: arithmetic expression: expecting primary: "0xffffffff * / 100"
usage: xprop [-options ...] [[format [dformat]] atom] ...

How do I fix this? Also, is there any way to set a default value for the $1 in case the user doesn't pass any command line argument?

2

1 Answer

It makes no sense (to me at least) to start a subshell within a shell function - particularly not a sh shell inside .bashrc

Instead, you could just do

opa(){ xprop -f _NET_WM_WINDOW_OPACITY 32c -set _NET_WM_WINDOW_OPACITY $(printf 0x%x $((0xffffffff * $1 / 100)))
}

If you want to supply a default value, you can do so using the ${parameter:-word} or ${parameter-word} syntax (depending on whether you want the default to take effect when $1 is undefined or empty, or only when it is undefined)

• BashGuide: Parameter Expansion

i.e.

opa(){ xprop -f _NET_WM_WINDOW_OPACITY 32c -set _NET_WM_WINDOW_OPACITY $(printf 0x%x $((0xffffffff * ${1:-60} / 100)))
}

If you really want to use a sh -c '...' subshell, you'd need to pass $1 from the parent bash shell into the child sh shell

opa(){ sh -c 'xprop -f _NET_WM_WINDOW_OPACITY 32c -set _NET_WM_WINDOW_OPACITY $(printf 0x%x $((0xffffffff * $1 / 100)))' sh "${1:-60}"
}

0

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