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.TH "GIT-UPDATE-REF" 1 "" "" ""
.SH NAME
git-update-ref \- update the object name stored in a ref safely
.SH "SYNOPSIS"


\fIgit\-update\-ref\fR <ref> <newvalue> [<oldvalue>]

.SH "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>\&.


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 \fIreal\fR 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)\&.


In general, using

.nf
git\-update\-ref HEAD "$head"
.fi


should be a _lot_ safer than doing

.nf
echo "$head" > "$GIT_DIR/HEAD"
.fi


both from a symlink following standpoint \fIand\fR 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)\&.

.SH "AUTHOR"


Written by Linus Torvalds <torvalds@osdl\&.org>\&.

.SH "GIT"


Part of the \fBgit\fR(7) suite