Why doesn't the "watch" command work on an alias?
So I've made my customized alias command and tried to use it with alias, but my alias was not recognized while concatenated with the watch command.
So I tried to make a thread of it and fortunately, this one helped me out.
But what is the reason for this?
I've created an alias in my .bashrc which works perfectly fine.
alias gpu='sensors nouveau-pci-0100'
alias cpu='sensors coretemp-isa-0000'
and when I concatenate watch and gpu like this:
watch GPU
I get this below every 2 seconds:
sh: 1: gpu: not found
And I solved it regarding the mentioned thread above like this:
alias = watchh='watch '
watchh gpu
But why does this happen? Why can' It use my surely defined alias command?
My guess is it is something about the user because I've gone root once and I couldn't use my alias but I surely need an expert to answer this.
It's nothing to do with users.
Aliases are only expanded in the interactive shell for which they are defined - so an interactive bash shell if you defined them via ~/.bashrc, or an interactive zsh shell if you define them in ~/.zshrc for example.
The watch command invokes commands via a non-interactive /bin/sh shell.
By aliasing watch itself, as alias watchh='watch ' (with a trailing space) and then using watchh gpu, you force the current interactive shell to expand gpu before it's passed to watch.
Note that in zsh, aliases may be defined as global which allows them to be expanded anywhere in a command - avoiding the need to alias watch with a trailing space.
The watch command does not locate aliases, only commands in your search path. As an alternative, define gpu and cpu as shell scripts instead of aliases and place them in your search path. Then your watch gpu and watch cpu commands will work fine.
For example, if $HOME/bin is a directory in your search path, create a file $HOME/bin/gpu containing the line:
sensors nouveau-pci-0100
Make the file executable:
$ chmod +x $HOME/bin/gpu
and you're ready to go!
$ watch gpu
Then do the same for cpu.