git-update-ref(1) ================= NAME ---- git-update-ref - Update the object name stored in a ref safely SYNOPSIS -------- [verse] 'git update-ref' [-m <reason>] [--no-deref] (-d <ref> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z]) DESCRIPTION ----------- Given two arguments, stores the <new-oid> in the <ref>, possibly dereferencing the symbolic refs. E.g. `git update-ref HEAD <new-oid>` updates the current branch head to the new object. Given three arguments, stores the <new-oid> in the <ref>, possibly dereferencing the symbolic refs, after verifying that the current value of the <ref> matches <old-oid>. E.g. `git update-ref refs/heads/master <new-oid> <old-oid>` updates the master branch head to <new-oid> only if its current value is <old-oid>. You can specify 40 "0" or an empty string as <old-oid> 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 <old-oid>. With `--stdin`, update-ref reads instructions from standard input and performs all modifications together. Specify commands of the form: update SP <ref> SP <new-oid> [SP <old-oid>] LF create SP <ref> SP <new-oid> LF delete SP <ref> [SP <old-oid>] LF verify SP <ref> [SP <old-oid>] LF symref-update SP <ref> SP <new-target> [SP (ref SP <old-target> | oid SP <old-oid>)] LF symref-create SP <ref> SP <new-target> LF symref-delete SP <ref> [SP <old-target>] LF symref-verify SP <ref> [SP <old-target>] LF option SP <opt> LF start LF prepare LF commit LF abort LF With `--create-reflog`, update-ref will create a reflog for each ref even if one would not ordinarily be created. Quote fields containing whitespace as if they were strings in C source code; i.e., surrounded by double-quotes and with backslash escapes. Use 40 "0" characters or the empty string to specify a zero value. To specify a missing value, omit the value and its preceding SP entirely. Alternatively, use `-z` to specify in NUL-terminated format, without quoting: update SP <ref> NUL <new-oid> NUL [<old-oid>] NUL create SP <ref> NUL <new-oid> NUL delete SP <ref> NUL [<old-oid>] NUL verify SP <ref> NUL [<old-oid>] NUL symref-update SP <ref> NUL <new-target> [NUL (ref NUL <old-target> | oid NUL <old-oid>)] NUL symref-create SP <ref> NUL <new-target> NUL symref-delete SP <ref> [NUL <old-target>] NUL symref-verify SP <ref> [NUL <old-target>] NUL option SP <opt> NUL start NUL prepare NUL commit NUL abort NUL In this format, use 40 "0" to specify a zero value, and use the empty string to specify a missing value. In either format, values can be specified in any form that Git recognizes as an object name. Commands in any other format or a repeated <ref> produce an error. Command meanings are: update:: Set <ref> to <new-oid> after verifying <old-oid>, if given. Specify a zero <new-oid> to ensure the ref does not exist after the update and/or a zero <old-oid> to make sure the ref does not exist before the update. create:: Create <ref> with <new-oid> after verifying it does not exist. The given <new-oid> may not be zero. delete:: Delete <ref> after verifying it exists with <old-oid>, if given. If given, <old-oid> may not be zero. symref-update:: Set <ref> to <new-target> after verifying <old-target> or <old-oid>, if given. Specify a zero <old-oid> to ensure that the ref does not exist before the update. verify:: Verify <ref> against <old-oid> but do not change it. If <old-oid> is zero or missing, the ref must not exist. symref-create: Create symbolic ref <ref> with <new-target> after verifying it does not exist. symref-delete:: Delete <ref> after verifying it exists with <old-target>, if given. symref-verify:: Verify symbolic <ref> against <old-target> but do not change it. If <old-target> is missing, the ref must not exist. Can only be used in `no-deref` mode. option:: Modify the behavior of the next command naming a <ref>. The only valid option is `no-deref` to avoid dereferencing a symbolic ref. start:: Start a transaction. In contrast to a non-transactional session, a transaction will automatically abort if the session ends without an explicit commit. This command may create a new empty transaction when the current one has been committed or aborted already. prepare:: Prepare to commit the transaction. This will create lock files for all queued reference updates. If one reference could not be locked, the transaction will be aborted. commit:: Commit all reference updates queued for the transaction, ending the transaction. abort:: Abort the transaction, releasing all locks if the transaction is in prepared state. If all <ref>s can be locked with matching <old-oid>s simultaneously, all modifications are performed. Otherwise, no modifications are performed. Note that while each individual <ref> 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 a pseudoref like HEAD or ORIG_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 <new-oid> 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