| git-update-ref(1) |
| ================= |
| |
| NAME |
| ---- |
| git-update-ref - Update the object name stored in a ref safely |
| |
| SYNOPSIS |
| -------- |
| [verse] |
| 'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>]) |
| |
| DESCRIPTION |
| ----------- |
| Given two arguments, stores the <newvalue> in the <ref>, possibly |
| dereferencing the symbolic refs. E.g. `git update-ref HEAD |
| <newvalue>` updates the current branch head to the new object. |
| |
| Given three arguments, stores the <newvalue> in the <ref>, |
| possibly dereferencing the symbolic refs, after verifying that |
| the current value of the <ref> matches <oldvalue>. |
| E.g. `git update-ref refs/heads/master <newvalue> <oldvalue>` |
| updates the master branch head to <newvalue> only if its current |
| value is <oldvalue>. You can specify 40 "0" or an empty string |
| as <oldvalue> 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, <ref> 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" > "$GIT_DIR/HEAD" |
| |
| both from a symlink following standpoint *and* an error checking |
| standpoint. The "refs/" rule for symlinks means that symlinks |
| that point to "outside" the tree are safe: they'll be followed |
| for reading but not for writing (so we'll never write through a |
| ref symlink to some other tree, if you have copied a whole |
| archive by creating a symlink tree). |
| |
| With `-d` flag, it deletes the named <ref> after verifying it |
| still contains <oldvalue>. |
| |
| |
| Logging Updates |
| --------------- |
| If config parameter "core.logAllRefUpdates" is true and the ref is one under |
| "refs/heads/", "refs/remotes/", "refs/notes/", or the symbolic ref HEAD; or |
| the file "$GIT_DIR/logs/<ref>" exists then `git update-ref` will append |
| a line to the log file "$GIT_DIR/logs/<ref>" (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 <ref>, "newsha1" is the 40 character hexadecimal value of |
| <newvalue> 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 <ref>) 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 |