$ git check-ref-format --branch @{-1}
git-check-ref-format - Ensures that a reference name is well formed
Checks if a given refname is acceptable, and exits with a non-zero status if it is not.
A reference is used in git to specify branches and tags. A branch head is stored under the $GIT_DIR/refs/heads directory, and a tag is stored under the $GIT_DIR/refs/tags directory (or, if refs are packed by git gc, as entries in the $GIT_DIR/packed-refs file). git imposes the following rules on how references are named:
They can include slash / for hierarchical (directory) grouping, but no slash-separated component can begin with a dot ..
They must contain at least one /. This enforces the presence of a category like heads/, tags/ etc. but the actual names are not restricted.
They cannot have two consecutive dots .. anywhere.
They cannot have ASCII control characters (i.e. bytes whose values are lower than \040, or \177 DEL), space, tilde ~, caret ^, colon :, question-mark ?, asterisk *, or open bracket [ anywhere.
They cannot end with a slash / nor a dot ..
They cannot end with the sequence .lock.
They cannot contain a sequence @{.
They cannot contain a \.
These rules make it easy for shell script based tools to parse reference names, pathname expansion by the shell when a reference name is used unquoted (by mistake), and also avoids ambiguities in certain reference name expressions (see gitrevisions(7)):
A double-dot .. is often used as in ref1..ref2, and in some contexts this notation means ^ref1 ref2 (i.e. not in ref1 and in ref2).
A tilde ~ and caret ^ are used to introduce the postfix nth parent and peel onion operation.
A colon : is used as in srcref:dstref to mean "use srcref’s value and store it in dstref" in fetch and push operations. It may also be used to select a specific object such as with git cat-file: "git cat-file blob v1.3.3:refs.c".
at-open-brace @{ is used as a notation to access a reflog entry.
With the --print option, if refname is acceptable, it prints the canonicalized name of a hypothetical reference with that name. That is, it prints refname with any extra / characters removed.
With the --branch option, it expands the “previous branch syntax” @{-n}. For example, @{-1} is a way to refer the last branch you were on. This option should be used by porcelains to accept this syntax anywhere a branch name is expected, so they can act as if you typed the branch name.
Print the name of the previous branch:
$ git check-ref-format --branch @{-1}
Determine the reference name to use for a new branch:
$ ref=$(git check-ref-format --print "refs/heads/$newbranch") || die "we do not like '$newbranch' as a branch name."
Part of the git(1) suite