I would like that whenever I run git diff or git show it silently automatically appends --ignore-all-space. Is there a way to do this
Take a look at the core.whitespace configuration variable.
I do not think so:
I do not see any "--ignore-all-space" option for git show
I cannot see git diff having the --ignore-all-space set automatically: it has to be passed as argument.
One solution for git diff at least would be to use git difftool.
Since it is a script (in <git>/libexec/git-core), you could modify that script to call git diff with that option always set.
But, that may not prove a good idea, since it can lead to ignore changes that not even you, the sender, had any chance to detect and test.