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diff --git a/Documentation/git-update-ref.txt b/Documentation/git-update-ref.txt new file mode 100644 index 0000000000..3e737c2360 --- /dev/null +++ b/Documentation/git-update-ref.txt @@ -0,0 +1,178 @@ +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> [<oldvalue>] | [--create-reflog] <ref> <newvalue> [<oldvalue>] | --stdin [-z]) + +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>. + +With `--stdin`, update-ref reads instructions from standard input and +performs all modifications together. Specify commands of the form: + + update SP <ref> SP <newvalue> [SP <oldvalue>] LF + create SP <ref> SP <newvalue> LF + delete SP <ref> [SP <oldvalue>] LF + verify SP <ref> [SP <oldvalue>] 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 <newvalue> NUL [<oldvalue>] NUL + create SP <ref> NUL <newvalue> NUL + delete SP <ref> NUL [<oldvalue>] NUL + verify SP <ref> NUL [<oldvalue>] 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 <newvalue> after verifying <oldvalue>, if given. + Specify a zero <newvalue> to ensure the ref does not exist + after the update and/or a zero <oldvalue> to make sure the + ref does not exist before the update. + +create:: + Create <ref> with <newvalue> after verifying it does not + exist. The given <newvalue> may not be zero. + +delete:: + Delete <ref> after verifying it exists with <oldvalue>, if + given. If given, <oldvalue> may not be zero. + +verify:: + Verify <ref> against <oldvalue> but do not change it. If + <oldvalue> is zero or missing, the ref must not exist. + +option:: + Modify 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. + +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 <oldvalue>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 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 |