git symbolic-ref [-m <reason>] <name> <ref> git symbolic-ref [-q] [--short] <name> git symbolic-ref --delete [-q] <name>
Given one argument, reads which branch head the given symbolic ref refers to and outputs its path, relative to the .git/ directory. Typically you would give HEAD as the <name> argument to see which branch your working tree is on.
Given two arguments, creates or updates a symbolic ref <name> to point at the given branch <ref>.
Given --delete and an additional argument, deletes the given symbolic ref.
In the past, .git/HEAD was a symbolic link pointing at refs/heads/master. When we wanted to switch to another branch, we did ln -sf refs/heads/newbranch .git/HEAD, and when we wanted to find out which branch we are on, we did readlink .git/HEAD. But symbolic links are not entirely portable, so they are now deprecated and symbolic refs (as described above) are used by default.
Part of the git(1) suite