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7dd4051b01
Add 'symref-update' command to the '--stdin' mode of 'git-update-ref' to allow updates of symbolic refs. The 'symref-update' command takes in a <new-target>, which the <ref> will be updated to. If the <ref> doesn't exist it will be created. It also optionally takes either an `ref <old-target>` or `oid <old-oid>`. If the <old-target> is provided, it checks to see if the <ref> targets the <old-target> before the update. If <old-oid> is provided it checks <ref> to ensure that it is a regular ref and <old-oid> is the OID before the update. This by extension also means that this when a zero <old-oid> is provided, it ensures that the ref didn't exist before. The divergence in syntax from the regular `update` command is because if we don't use a `(ref | oid)` prefix for the old_value, then there is ambiguity around if the value provided should be treated as an oid or a reference. This is more so the reason, because we allow anything committish to be provided as an oid. While 'symref-verify' and 'symref-delete' also take in `<old-target>` we do not have this divergence there as those commands only work with symrefs. Whereas 'symref-update' also works with regular refs and allows users to convert regular refs to symrefs. The command allows users to perform symbolic ref updates within a transaction. This provides atomicity and allows users to perform a set of operations together. This command supports deref mode, to ensure that we can update dereferenced regular refs to symrefs. Helped-by: Patrick Steinhardt <ps@pks.im> Helped-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Karthik Nayak <karthik.188@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
206 lines
7.1 KiB
Plaintext
206 lines
7.1 KiB
Plaintext
git-update-ref(1)
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=================
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NAME
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----
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git-update-ref - Update the object name stored in a ref safely
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SYNOPSIS
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--------
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[verse]
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'git update-ref' [-m <reason>] [--no-deref] (-d <ref> [<old-oid>] | [--create-reflog] <ref> <new-oid> [<old-oid>] | --stdin [-z])
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DESCRIPTION
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-----------
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Given two arguments, stores the <new-oid> in the <ref>, possibly
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dereferencing the symbolic refs. E.g. `git update-ref HEAD
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<new-oid>` updates the current branch head to the new object.
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Given three arguments, stores the <new-oid> in the <ref>,
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possibly dereferencing the symbolic refs, after verifying that
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the current value of the <ref> matches <old-oid>.
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E.g. `git update-ref refs/heads/master <new-oid> <old-oid>`
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updates the master branch head to <new-oid> only if its current
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value is <old-oid>. You can specify 40 "0" or an empty string
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as <old-oid> to make sure that the ref you are creating does
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not exist.
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It also allows a "ref" file to be a symbolic pointer to another
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ref file by starting with the four-byte header sequence of
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"ref:".
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More importantly, it allows the update of a ref file to follow
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these symbolic pointers, whether they are symlinks or these
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"regular file symbolic refs". It follows *real* symlinks only
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if they start with "refs/": otherwise it will just try to read
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them and update them as a regular file (i.e. it will allow the
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filesystem to follow them, but will overwrite such a symlink to
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somewhere else with a regular filename).
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If --no-deref is given, <ref> itself is overwritten, rather than
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the result of following the symbolic pointers.
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In general, using
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git update-ref HEAD "$head"
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should be a _lot_ safer than doing
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echo "$head" > "$GIT_DIR/HEAD"
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both from a symlink following standpoint *and* an error checking
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standpoint. The "refs/" rule for symlinks means that symlinks
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that point to "outside" the tree are safe: they'll be followed
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for reading but not for writing (so we'll never write through a
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ref symlink to some other tree, if you have copied a whole
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archive by creating a symlink tree).
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With `-d` flag, it deletes the named <ref> after verifying it
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still contains <old-oid>.
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With `--stdin`, update-ref reads instructions from standard input and
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performs all modifications together. Specify commands of the form:
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update SP <ref> SP <new-oid> [SP <old-oid>] LF
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create SP <ref> SP <new-oid> LF
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delete SP <ref> [SP <old-oid>] LF
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verify SP <ref> [SP <old-oid>] LF
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symref-update SP <ref> SP <new-target> [SP (ref SP <old-target> | oid SP <old-oid>)] LF
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symref-create SP <ref> SP <new-target> LF
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symref-delete SP <ref> [SP <old-target>] LF
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symref-verify SP <ref> [SP <old-target>] LF
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option SP <opt> LF
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start LF
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prepare LF
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commit LF
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abort LF
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With `--create-reflog`, update-ref will create a reflog for each ref
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even if one would not ordinarily be created.
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Quote fields containing whitespace as if they were strings in C source
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code; i.e., surrounded by double-quotes and with backslash escapes.
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Use 40 "0" characters or the empty string to specify a zero value. To
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specify a missing value, omit the value and its preceding SP entirely.
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Alternatively, use `-z` to specify in NUL-terminated format, without
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quoting:
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update SP <ref> NUL <new-oid> NUL [<old-oid>] NUL
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create SP <ref> NUL <new-oid> NUL
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delete SP <ref> NUL [<old-oid>] NUL
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verify SP <ref> NUL [<old-oid>] NUL
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symref-update SP <ref> NUL <new-target> [NUL (ref NUL <old-target> | oid NUL <old-oid>)] NUL
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symref-create SP <ref> NUL <new-target> NUL
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symref-delete SP <ref> [NUL <old-target>] NUL
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symref-verify SP <ref> [NUL <old-target>] NUL
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option SP <opt> NUL
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start NUL
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prepare NUL
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commit NUL
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abort NUL
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In this format, use 40 "0" to specify a zero value, and use the empty
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string to specify a missing value.
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In either format, values can be specified in any form that Git
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recognizes as an object name. Commands in any other format or a
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repeated <ref> produce an error. Command meanings are:
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update::
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Set <ref> to <new-oid> after verifying <old-oid>, if given.
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Specify a zero <new-oid> to ensure the ref does not exist
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after the update and/or a zero <old-oid> to make sure the
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ref does not exist before the update.
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create::
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Create <ref> with <new-oid> after verifying it does not
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exist. The given <new-oid> may not be zero.
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delete::
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Delete <ref> after verifying it exists with <old-oid>, if
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given. If given, <old-oid> may not be zero.
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symref-update::
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Set <ref> to <new-target> after verifying <old-target> or <old-oid>,
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if given. Specify a zero <old-oid> to ensure that the ref does not
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exist before the update.
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verify::
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Verify <ref> against <old-oid> but do not change it. If
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<old-oid> is zero or missing, the ref must not exist.
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symref-create:
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Create symbolic ref <ref> with <new-target> after verifying
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it does not exist.
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symref-delete::
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Delete <ref> after verifying it exists with <old-target>, if given.
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symref-verify::
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Verify symbolic <ref> against <old-target> but do not change it.
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If <old-target> is missing, the ref must not exist. Can only be
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used in `no-deref` mode.
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option::
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Modify the behavior of the next command naming a <ref>.
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The only valid option is `no-deref` to avoid dereferencing
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a symbolic ref.
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start::
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Start a transaction. In contrast to a non-transactional session, a
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transaction will automatically abort if the session ends without an
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explicit commit. This command may create a new empty transaction when
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the current one has been committed or aborted already.
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prepare::
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Prepare to commit the transaction. This will create lock files for all
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queued reference updates. If one reference could not be locked, the
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transaction will be aborted.
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commit::
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Commit all reference updates queued for the transaction, ending the
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transaction.
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abort::
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Abort the transaction, releasing all locks if the transaction is in
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prepared state.
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If all <ref>s can be locked with matching <old-oid>s
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simultaneously, all modifications are performed. Otherwise, no
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modifications are performed. Note that while each individual
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<ref> is updated or deleted atomically, a concurrent reader may
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still see a subset of the modifications.
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LOGGING UPDATES
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---------------
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If config parameter "core.logAllRefUpdates" is true and the ref is one
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under "refs/heads/", "refs/remotes/", "refs/notes/", or a pseudoref
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like HEAD or ORIG_HEAD; or the file "$GIT_DIR/logs/<ref>" exists then
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`git update-ref` will append a line to the log file
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"$GIT_DIR/logs/<ref>" (dereferencing all symbolic refs before creating
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the log name) describing the change in ref value. Log lines are
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formatted as:
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oldsha1 SP newsha1 SP committer LF
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Where "oldsha1" is the 40 character hexadecimal value previously
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stored in <ref>, "newsha1" is the 40 character hexadecimal value of
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<new-oid> and "committer" is the committer's name, email address
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and date in the standard Git committer ident format.
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Optionally with -m:
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oldsha1 SP newsha1 SP committer TAB message LF
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Where all fields are as described above and "message" is the
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value supplied to the -m option.
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An update will fail (without changing <ref>) if the current user is
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unable to create a new log file, append to the existing log file
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or does not have committer information available.
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GIT
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---
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Part of the linkgit:git[1] suite
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