fetch.c: do not call process_tree() from process_tree().
[git/git.git] / Documentation / git-update-ref.txt
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