git-update-ref(1) ================= NAME ---- git-update-ref - Update the object name stored in a ref safely SYNOPSIS -------- [verse] 'git update-ref' [-m ] (-d [] | [--no-deref] [] | --stdin [-z]) DESCRIPTION ----------- Given two arguments, stores the in the , possibly dereferencing the symbolic refs. E.g. `git update-ref HEAD ` updates the current branch head to the new object. Given three arguments, stores the in the , possibly dereferencing the symbolic refs, after verifying that the current value of the matches . E.g. `git update-ref refs/heads/master ` updates the master branch head to only if its current value is . You can specify 40 "0" or an empty string as to make sure that the ref you are creating does not exist. It also allows a "ref" file to be a symbolic pointer to another ref file by starting with the four-byte header sequence of "ref:". More importantly, it allows the update of a ref file to follow these symbolic pointers, whether they are symlinks or these "regular file symbolic refs". It follows *real* symlinks only if they start with "refs/": otherwise it will just try to read them and update them as a regular file (i.e. it will allow the filesystem to follow them, but will overwrite such a symlink to somewhere else with a regular filename). If --no-deref is given, itself is overwritten, rather than the result of following the symbolic pointers. In general, using git update-ref HEAD "$head" should be a _lot_ safer than doing echo "$head" > "$GIT_DIR/HEAD" both from a symlink following standpoint *and* an error checking standpoint. The "refs/" rule for symlinks means that symlinks that point to "outside" the tree are safe: they'll be followed for reading but not for writing (so we'll never write through a ref symlink to some other tree, if you have copied a whole archive by creating a symlink tree). With `-d` flag, it deletes the named after verifying it still contains . With `--stdin`, update-ref reads instructions from standard input and performs all modifications together. Specify commands of the form: update SP SP [SP ] LF create SP SP LF delete SP [SP ] LF verify SP [SP ] LF option SP LF Quote fields containing whitespace as if they were strings in C source code. Alternatively, use `-z` to specify commands without quoting: update SP NUL NUL [] NUL create SP NUL NUL delete SP NUL [] NUL verify SP NUL [] NUL option SP NUL Lines of any other format or a repeated produce an error. Command meanings are: update:: Set to after verifying , if given. Specify a zero to ensure the ref does not exist after the update and/or a zero to make sure the ref does not exist before the update. create:: Create with after verifying it does not exist. The given may not be zero. delete:: Delete after verifying it exists with , if given. If given, may not be zero. verify:: Verify against but do not change it. If zero or missing, the ref must not exist. option:: Modify behavior of the next command naming a . The only valid option is `no-deref` to avoid dereferencing a symbolic ref. Use 40 "0" or the empty string to specify a zero value, except that with `-z` an empty is considered missing. If all s can be locked with matching s simultaneously, all modifications are performed. Otherwise, no modifications are performed. Note that while each individual is updated or deleted atomically, a concurrent reader may still see a subset of the modifications. Logging Updates --------------- If config parameter "core.logAllRefUpdates" is true and the ref is one under "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic ref HEAD; or the file "$GIT_DIR/logs/" exists then `git update-ref` will append a line to the log file "$GIT_DIR/logs/" (dereferencing all symbolic refs before creating the log name) describing the change in ref value. Log lines are formatted as: . oldsha1 SP newsha1 SP committer LF + Where "oldsha1" is the 40 character hexadecimal value previously stored in , "newsha1" is the 40 character hexadecimal value of and "committer" is the committer's name, email address and date in the standard Git committer ident format. Optionally with -m: . oldsha1 SP newsha1 SP committer TAB message LF + Where all fields are as described above and "message" is the value supplied to the -m option. An update will fail (without changing ) if the current user is unable to create a new log file, append to the existing log file or does not have committer information available. GIT --- Part of the linkgit:git[1] suite