Answer by cagney for How to get the current branch name in Git?

Using earlier ideas; assuming sha1 is 40 characters; and chasing references (yea, should delete the debug print lines :-):

git reflog | awk '
$3 == "checkout:" && (sha == "" || sha == $1 ) {
  from=$(NF - 2)
  to=$NF
  print from, to, length(from) > "/dev/stderr"
  if (length(from) != 40) { print from ; exit; }
  sha=substr(from, 1, 7)
  print sha > "/dev/stderr"
}
'

gives the raw output:

$ git status
HEAD detached at 147049c
[...]
$ ./gime-branch.sh
a47be8d2167641088b66bf8f5c2bf7d3da0c642c HEAD^ 40
a47be8d
master HEAD^ 6
master