Pipes in a Git alias?
I don't think you can, but you can prefix it with an ! to treat the command as a new shell command
[alias]
pushcur = ! git branch | grep '*' …
I typically make small git- scripts and put them in a directory that's in my path (~/.local/bin). Check out git-extras for a bunch of good examples.
A simple workaround is to add it as shell alias.
Here is an example:
alias grf="git rebase -i $(git merge-base --fork-point master)"
(rebase on the fork commit of current branch and master interactively)
For bash, add it to ~/.bashrc, then you can simply use grf.