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diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt new file mode 100644 index 0000000000..3d4b79c480 --- /dev/null +++ b/Documentation/revisions.txt @@ -0,0 +1,201 @@ +SPECIFYING REVISIONS +-------------------- + +A revision parameter typically, but not necessarily, names a +commit object. They use what is called an 'extended SHA1' +syntax. Here are various ways to spell object names. The +ones listed near the end of this list are to name trees and +blobs contained in a commit. + +* The full SHA1 object name (40-byte hexadecimal string), or + a substring of such that is unique within the repository. + E.g. dae86e1950b1277e545cee180551750029cfe735 and dae86e both + name the same commit object if there are no other object in + your repository whose object name starts with dae86e. + +* An output from 'git describe'; i.e. a closest tag, optionally + followed by a dash and a number of commits, followed by a dash, a + `g`, and an abbreviated object name. + +* A symbolic ref name. E.g. 'master' typically means the commit + object referenced by refs/heads/master. If you + happen to have both heads/master and tags/master, you can + explicitly say 'heads/master' to tell git which one you mean. + When ambiguous, a `<name>` is disambiguated by taking the + first match in the following rules: + + . if `$GIT_DIR/<name>` exists, that is what you mean (this is usually + useful only for `HEAD`, `FETCH_HEAD`, `ORIG_HEAD` and `MERGE_HEAD`); + + . otherwise, `refs/<name>` if exists; + + . otherwise, `refs/tags/<name>` if exists; + + . otherwise, `refs/heads/<name>` if exists; + + . otherwise, `refs/remotes/<name>` if exists; + + . otherwise, `refs/remotes/<name>/HEAD` if exists. ++ +HEAD names the commit your changes in the working tree is based on. +FETCH_HEAD records the branch you fetched from a remote repository +with your last 'git fetch' invocation. +ORIG_HEAD is created by commands that moves your HEAD in a drastic +way, to record the position of the HEAD before their operation, so that +you can change the tip of the branch back to the state before you ran +them easily. +MERGE_HEAD records the commit(s) you are merging into your branch +when you run 'git merge'. ++ +Note that any of the `refs/*` cases above may come either from +the `$GIT_DIR/refs` directory or from the `$GIT_DIR/packed-refs` file. + +* A ref followed by the suffix '@' with a date specification + enclosed in a brace + pair (e.g. '\{yesterday\}', '\{1 month 2 weeks 3 days 1 hour 1 + second ago\}' or '\{1979-02-26 18:30:00\}') to specify the value + of the ref at a prior point in time. This suffix may only be + used immediately following a ref name and the ref must have an + existing log ($GIT_DIR/logs/<ref>). Note that this looks up the state + of your *local* ref at a given time; e.g., what was in your local + `master` branch last week. If you want to look at commits made during + certain times, see `--since` and `--until`. + +* A ref followed by the suffix '@' with an ordinal specification + enclosed in a brace pair (e.g. '\{1\}', '\{15\}') to specify + the n-th prior value of that ref. For example 'master@\{1\}' + is the immediate prior value of 'master' while 'master@\{5\}' + is the 5th prior value of 'master'. This suffix may only be used + immediately following a ref name and the ref must have an existing + log ($GIT_DIR/logs/<ref>). + +* You can use the '@' construct with an empty ref part to get at a + reflog of the current branch. For example, if you are on the + branch 'blabla', then '@\{1\}' means the same as 'blabla@\{1\}'. + +* The special construct '@\{-<n>\}' means the <n>th branch checked out + before the current one. + +* The suffix '@\{upstream\}' to a ref (short form 'ref@\{u\}') refers to + the branch the ref is set to build on top of. Missing ref defaults + to the current branch. + +* A suffix '{caret}' to a revision parameter (e.g. 'HEAD{caret}') means the first parent of + that commit object. '{caret}<n>' means the <n>th parent (i.e. + 'rev{caret}' + is equivalent to 'rev{caret}1'). As a special rule, + 'rev{caret}0' means the commit itself and is used when 'rev' is the + object name of a tag object that refers to a commit object. + +* A suffix '{tilde}<n>' to a revision parameter means the commit + object that is the <n>th generation grand-parent of the named + commit object, following only the first parent. I.e. rev~3 is + equivalent to rev{caret}{caret}{caret} which is equivalent to + rev{caret}1{caret}1{caret}1. See below for a illustration of + the usage of this form. + +* A suffix '{caret}' followed by an object type name enclosed in + brace pair (e.g. `v0.99.8{caret}\{commit\}`) means the object + could be a tag, and dereference the tag recursively until an + object of that type is found or the object cannot be + dereferenced anymore (in which case, barf). `rev{caret}0` + introduced earlier is a short-hand for `rev{caret}\{commit\}`. + +* A suffix '{caret}' followed by an empty brace pair + (e.g. `v0.99.8{caret}\{\}`) means the object could be a tag, + and dereference the tag recursively until a non-tag object is + found. + +* A colon, followed by a slash, followed by a text (e.g. `:/fix nasty bug`): this names + a commit whose commit message matches the specified regular expression. + This name returns the youngest matching commit which is + reachable from any ref. If the commit message starts with a + '!', you have to repeat that; the special sequence ':/!', + followed by something else than '!' is reserved for now. + The regular expression can match any part of the commit message. To + match messages starting with a string, one can use e.g. `:/^foo`. + +* A suffix ':' followed by a path (e.g. `HEAD:README`); this names the blob or tree + at the given path in the tree-ish object named by the part + before the colon. + ':path' (with an empty part before the colon, e.g. `:README`) + is a special case of the syntax described next: content + recorded in the index at the given path. + +* A colon, optionally followed by a stage number (0 to 3) and a + colon, followed by a path (e.g. `:0:README`); this names a blob object in the + index at the given path. Missing stage number (and the colon + that follows it, e.g. `:README`) names a stage 0 entry. During a merge, stage + 1 is the common ancestor, stage 2 is the target branch's version + (typically the current branch), and stage 3 is the version from + the branch being merged. + +Here is an illustration, by Jon Loeliger. Both commit nodes B +and C are parents of commit node A. Parent commits are ordered +left-to-right. + +........................................ +G H I J + \ / \ / + D E F + \ | / \ + \ | / | + \|/ | + B C + \ / + \ / + A +........................................ + + A = = A^0 + B = A^ = A^1 = A~1 + C = A^2 = A^2 + D = A^^ = A^1^1 = A~2 + E = B^2 = A^^2 + F = B^3 = A^^3 + G = A^^^ = A^1^1^1 = A~3 + H = D^2 = B^^2 = A^^^2 = A~2^2 + I = F^ = B^3^ = A^^3^ + J = F^2 = B^3^2 = A^^3^2 + + +SPECIFYING RANGES +----------------- + +History traversing commands such as 'git log' operate on a set +of commits, not just a single commit. To these commands, +specifying a single revision with the notation described in the +previous section means the set of commits reachable from that +commit, following the commit ancestry chain. + +To exclude commits reachable from a commit, a prefix `{caret}` +notation is used. E.g. `{caret}r1 r2` means commits reachable +from `r2` but exclude the ones reachable from `r1`. + +This set operation appears so often that there is a shorthand +for it. When you have two commits `r1` and `r2` (named according +to the syntax explained in SPECIFYING REVISIONS above), you can ask +for commits that are reachable from r2 excluding those that are reachable +from r1 by `{caret}r1 r2` and it can be written as `r1..r2`. + +A similar notation `r1\...r2` is called symmetric difference +of `r1` and `r2` and is defined as +`r1 r2 --not $(git merge-base --all r1 r2)`. +It is the set of commits that are reachable from either one of +`r1` or `r2` but not from both. + +Two other shorthands for naming a set that is formed by a commit +and its parent commits exist. The `r1{caret}@` notation means all +parents of `r1`. `r1{caret}!` includes commit `r1` but excludes +all of its parents. + +Here are a handful of examples: + + D G H D + D F G H I J D F + ^G D H D + ^D B E I J F B + B...C G H D E B C + ^D B C E I J F B C + C^@ I J F + F^! D G H D F |