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rit commit-tree

Create a commit object from a tree hash.

Synopsis​

rit commit-tree <tree-hash> -m <message> [-p <parent>]...

Description​

This plumbing command creates a commit object from a tree hash. It's the low-level command for creating commits - the high-level commit command (coming in Commit 10) will use this internally.

Options​

OptionDescription
-m, --message <message>Commit message (required)
-p, --parent <hash>Parent commit hash (can be specified multiple times for merge commits)

Commit Object Format​

A commit object contains:

tree <tree-sha1>
parent <parent-sha1>     # 0 or more parent lines
author <name> <email> <timestamp> <timezone>
committer <name> <email> <timestamp> <timezone>

<commit message>

Examples​

Initial Commit (No Parent)​

# Create a tree first
$ rit write-tree
a1b2c3d4e5f6789abcdef0123456789abcdef0123

# Create commit from tree
$ rit commit-tree a1b2c3d4e5f6789abcdef0123456789abcdef0123 -m "Initial commit"
7b539874eb3d54acf7f30f2d38e74307bfb3c3d8

# Read the commit back
$ rit cat-file -p 7b539874eb3d54acf7f30f2d38e74307bfb3c3d8
tree a1b2c3d4e5f6789abcdef0123456789abcdef0123
author Your Name <you@example.com> 1234567890 +0000
committer Your Name <you@example.com> 1234567890 +0000

Initial commit

Commit with Parent​

# First commit
$ TREE1=$(rit write-tree)
$ COMMIT1=$(rit commit-tree $TREE1 -m "First commit")

# Second commit (with parent)
$ echo "new file" > new.txt
$ TREE2=$(rit write-tree)
$ COMMIT2=$(rit commit-tree $TREE2 -m "Second commit" -p $COMMIT1)

# Verify parent relationship
$ rit cat-file -p $COMMIT2
tree <tree2-hash>
parent <commit1-hash>
author ...
committer ...

Second commit

Merge Commit (Multiple Parents)​

# Create merge commit with two parents
$ rit commit-tree <tree-hash> -m "Merge branches" -p <parent1> -p <parent2>

Author Information​

The command automatically detects author information from:

  1. Environment variables:

    • GIT_AUTHOR_NAME / GIT_COMMITTER_NAME
    • GIT_AUTHOR_EMAIL / GIT_COMMITTER_EMAIL

  2. System defaults:

    • Username from $USER or $USERNAME
    • Email: <username>@localhost

Use Cases​

Creating Your First Commit​

# 1. Initialize repository
$ rit init

# 2. Create some files
$ echo "Hello" > hello.txt

# 3. Create tree
$ TREE=$(rit write-tree)

# 4. Create commit
$ COMMIT=$(rit commit-tree $TREE -m "Initial commit")
$ echo $COMMIT > .rit/refs/heads/main  # Point branch to commit

Building Commit History​

# Commit 1
$ TREE1=$(rit write-tree)
$ COMMIT1=$(rit commit-tree $TREE1 -m "First")

# Commit 2 (child of commit 1)
$ # ... make changes ...
$ TREE2=$(rit write-tree)
$ COMMIT2=$(rit commit-tree $TREE2 -m "Second" -p $COMMIT1)

# Commit 3 (child of commit 2)
$ # ... make changes ...
$ TREE3=$(rit write-tree)
$ COMMIT3=$(rit commit-tree $TREE3 -m "Third" -p $COMMIT2)

Verify Against Real Git​

You can verify your implementation matches Git:

# Using Git
$ git init
$ echo "test" > test.txt
$ git add test.txt
$ TREE=$(git write-tree)
$ COMMIT=$(git commit-tree $TREE -m "test")
$ git cat-file -p $COMMIT

# Using Rit (should match!)
$ rit init
$ echo "test" > test.txt
$ TREE=$(rit write-tree)
$ COMMIT=$(rit commit-tree $TREE -m "test")
$ rit cat-file -p $COMMIT

Implementation Details​

Commit Creation Process​

  1. Verify tree object exists
  2. Get author/committer info (from env or defaults)
  3. Create Commit struct
  4. Serialize to Git format
  5. Store as object (hash + compress)
  6. Return commit hash

Timestamp​

The commit uses the current Unix timestamp (seconds since epoch) for both author and committer times.

See Also​

  • write-tree - Create tree objects
  • cat-file - Read commit objects
  • log - View commit history (coming in Commit 8)
  • Architecture - Commit object format details