git-check-ref-format - Man Page

• Check the format of the specified reference name: git check-ref-format refs/head/refname
• Print the name of the last branch checked out: git check-ref-format --branch @{-1}
• Normalize a refname: git check-ref-format --normalize refs/head/refname

tldr.sh

git check-ref-format [--normalize]
       [--[no-]allow-onelevel] [--refspec-pattern]
       <refname>
git check-ref-format --branch <branchname-shorthand>

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 in the refs/heads hierarchy, while a tag is stored in the refs/tags hierarchy of the ref namespace (typically in $GIT_DIR/refs/heads and $GIT_DIR/refs/tags directories or, as entries in file $GIT_DIR/packed-refs if refs are packed by git gc)​.

Git imposes the following rules on how references are named:

1. They can include slash / for hierarchical (directory) grouping, but no slash-separated component can begin with a dot ​. or end with the sequence ​.lock​.
2. They must contain at least one /​. This enforces the presence of a category like heads/, tags/ etc​. but the actual names are not restricted​. If the --allow-onelevel option is used, this rule is waived​.
3. They cannot have two consecutive dots ​.​. anywhere​.
4. They cannot have ASCII control characters (i​.e​. bytes whose values are lower than \040, or \177 DEL), space, tilde ~, caret ^, or colon : anywhere​.
5. They cannot have question-mark ?, asterisk *, or open bracket [ anywhere​. See the --refspec-pattern option below for an exception to this rule​.
6. They cannot begin or end with a slash / or contain multiple consecutive slashes (see the --normalize option below for an exception to this rule)​.
7. They cannot end with a dot ​.​.
8. They cannot contain a sequence @{​.
9. They cannot be the single character @​.
10. 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 avoid ambiguities in certain reference name expressions (see gitrevisions(7)):

1. 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)​.
2. A tilde ~ and caret ^ are used to introduce the postfix nth parent and peel onion operation​.
3. 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"​.
4. at-open-brace @{ is used as a notation to access a reflog entry​.

With the --branch option, the command takes a name and checks if it can be used as a valid branch name (e​.g​. when creating a new branch)​. But be cautious when using the previous checkout syntax that may refer to a detached HEAD state​. The rule git check-ref-format --branch $name implements may be stricter than what git check-ref-format refs/heads/$name says (e​.g​. a dash may appear at the beginning of a ref component, but it is explicitly forbidden at the beginning of a branch name)​. When run with the --branch option in a repository, the input is first expanded for the “previous checkout syntax” @{-n}​. For example, @{-1} is a way to refer the last thing that was checked out using "git switch" or "git checkout" operation​. 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​. As an exception note that, the “previous checkout operation” might result in a commit object name when the N-th last thing checked out was not a branch​.

--allow-onelevel,  --no-allow-onelevel

Controls whether one-level refnames are accepted (i​.e​., refnames that do not contain multiple /-separated components)​. The default is --no-allow-onelevel​.

--refspec-pattern

Interpret <refname> as a reference name pattern for a refspec (as used with remote repositories)​. If this option is enabled, <refname> is allowed to contain a single * in the refspec (e​.g​., foo/bar*/baz or foo/bar*baz/ but not foo/bar*/baz*)​.

--normalize

Normalize refname by removing any leading slash (/) characters and collapsing runs of adjacent slashes between name components into a single slash​. If the normalized refname is valid then print it to standard output and exit with a status of 0, otherwise exit with a non-zero status​. (--print is a deprecated way to spell --normalize​.)

• Print the name of the previous thing checked out:

  $ git check-ref-format --branch @{-1}

• Determine the reference name to use for a new branch:

  $ ref=$(git check-ref-format --normalize "refs/heads/$newbranch")||
  { echo "we do not like '$newbranch' as a branch name​." >&2 ; exit 1 ; }

Part of the git(1) suite