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12905637 JH |
1 | git-update-ref(1) |
2 | ================= | |
3 | ||
4 | NAME | |
5 | ---- | |
6 | git-update-ref - update the object name stored in a ref safely | |
7 | ||
8 | SYNOPSIS | |
9 | -------- | |
10 | `git-update-ref` <ref> <newvalue> [<oldvalue>] | |
11 | ||
12 | DESCRIPTION | |
13 | ----------- | |
14 | Given two arguments, stores the <newvalue> in the <ref>, possibly | |
15 | dereferencing the symbolic refs. E.g. `git-update-ref HEAD | |
16 | <newvalue>` updates the current branch head to the new object. | |
17 | ||
18 | Given three arguments, stores the <newvalue> in the <ref>, | |
19 | possibly dereferencing the symbolic refs, after verifying that | |
20 | the current value of the <ref> matches <oldvalue>. | |
21 | E.g. `git-update-ref refs/heads/master <newvalue> <oldvalue>` | |
22 | updates the master branch head to <newvalue> only if its current | |
23 | value is <oldvalue>. | |
24 | ||
25 | It also allows a "ref" file to be a symbolic pointer to another | |
26 | ref file by starting with the four-byte header sequence of | |
27 | "ref:". | |
28 | ||
29 | More importantly, it allows the update of a ref file to follow | |
30 | these symbolic pointers, whether they are symlinks or these | |
31 | "regular file symbolic refs". It follows *real* symlinks only | |
32 | if they start with "refs/": otherwise it will just try to read | |
33 | them and update them as a regular file (i.e. it will allow the | |
34 | filesystem to follow them, but will overwrite such a symlink to | |
35 | somewhere else with a regular filename). | |
36 | ||
37 | In general, using | |
38 | ||
39 | git-update-ref HEAD "$head" | |
40 | ||
41 | should be a _lot_ safer than doing | |
42 | ||
43 | echo "$head" > "$GIT_DIR/HEAD" | |
44 | ||
45 | both from a symlink following standpoint *and* an error checking | |
46 | standpoint. The "refs/" rule for symlinks means that symlinks | |
47 | that point to "outside" the tree are safe: they'll be followed | |
48 | for reading but not for writing (so we'll never write through a | |
49 | ref symlink to some other tree, if you have copied a whole | |
50 | archive by creating a symlink tree). | |
51 | ||
52 | Author | |
53 | ------ | |
54 | Written by Linus Torvalds <torvalds@osdl.org>. | |
55 | ||
56 | GIT | |
57 | --- | |
58 | Part of the gitlink:git[7] suite |