freshlybakedca.ke
Git fork
Merge branch 'dg/user-manual-hash-example'
User manual (the original one) update.
* dg/user-manual-hash-example:
Documentation/user-manual.txt: example for generating object hashes
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Documentation/user-manual.txt
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Documentation/user-manual.txt
···
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about the data in the object. It's worth noting that the SHA-1 hash
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that is used to name the object is the hash of the original data
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plus this header, so `sha1sum` 'file' does not match the object name
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for 'file'.
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for 'file' (the earliest versions of Git hashed slightly differently
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but the conclusion is still the same).
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The following is a short example that demonstrates how these hashes
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can be generated manually:
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Let's assume a small text file with some simple content:
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-------------------------------------------------
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$ echo "Hello world" >hello.txt
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-------------------------------------------------
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We can now manually generate the hash Git would use for this file:
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- The object we want the hash for is of type "blob" and its size is
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12 bytes.
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- Prepend the object header to the file content and feed this to
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`sha1sum`:
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-------------------------------------------------
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$ { printf "blob 12\0"; cat hello.txt; } | sha1sum
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802992c4220de19a90767f3000a79a31b98d0df7 -
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-------------------------------------------------
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This manually constructed hash can be verified using `git hash-object`
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which of course hides the addition of the header:
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-------------------------------------------------
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$ git hash-object hello.txt
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802992c4220de19a90767f3000a79a31b98d0df7
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-------------------------------------------------
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As a result, the general consistency of an object can always be tested
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independently of the contents or the type of the object: all objects can
···
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----------------------------------------------------
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The initial revision lays the foundation for almost everything Git has
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today, but is small enough to read in one sitting.
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today (even though details may differ in a few places), but is small
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enough to read in one sitting.
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Note that terminology has changed since that revision. For example, the
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README in that revision uses the word "changeset" to describe what we