interpret-trailers Git Command Guide

The git interpret-trailers command adds or parses structured trailer lines in commit messages, enabling automated management of metadata like issue tracking, signed-off-by lines, and review information.

git interpret-trailers Syntax:

git interpret-trailers [--in-place] [--trim-empty] [--only-trailers] [--only-input]
                       [--where[=<action>]]
                       [--if-exists[=<action>] || --if-missing[=<action>]]
                       [--no-divider | [--[no-]divider]]
                       [<token>[(=|:)<value>]]…] [<file>]

Options:

Option	Description
--in-place	Edit file in-place instead of stdout
--trim-empty	Remove empty trailers
--only-trailers	Output only trailer lines
--only-input	Output only input without trailers
--where=<action>	Add after (after) or before (before)
--if-exists=<action>	Add-only, do-nothing, replace
--if-missing=<action>	Add-only, do-nothing
--no-divider	Use no divider
--divider	Add divider before trailers

Parameters:

Parameter	Description
`[(=	:)]`
<file>	File to process (stdin if not specified)

Trailer Format and Structure:

Standard Trailer Examples:

# Signed-off-by trailer
Signed-off-by: Developer Name <developer@example.com>

# Fixes issue reference
Fixes: #123

# Reviewed-by annotation
Reviewed-by: Code Reviewer <reviewer@company.com>

# Co-authored-by trailer
Co-authored-by: Collaborator Name <collaborator@example.com>

# Custom metadata trailers
Priority: high
Severity: critical
Closes: #456, #789

Trailer Recognition Rules:

# Valid trailer line formats:
token: value
token # value
token value (with tab or space separation)

# Case-insensitive tokens
Bug: #123
bug: #123

# Multi-word tokens
Signed-off-by: Developer <dev@example.com>

Usage Patterns:

Add Single Trailer:

# Add signed-off-by trailer
echo "Fixed bug in parser" | git interpret-trailers --trailer "Signed-off-by: $(git config user.name) <$(git config user.email)>"

# Add issue reference
git interpret-trailers --trailer "Fixes: #123" --in-place COMMIT_MSG

Process Existing Message:

# Read commit message and add trailer
cat COMMIT_MSG | git interpret-trailers --trailer "Reviewed-by: $(git config user.name)"

# Process file in-place
git interpret-trailers --trailer "Tested-by: QA Team" --in-place COMMIT_MSG

Conditional Trailer Addition:

# Add only if missing
git interpret-trailers --if-missing addIfMissing --trailer "Signed-off-by: $(git config user.name) <$(git config user.email)>"

# Replace existing trailer
git interpret-trailers --if-exists replace --trailer "Status: reviewed"

# Skip if trailer exists
git interpret-trailers --if-exists doNothing --trailer "Priority: high"

Trailer Location Control:

# Add after existing trailers
git interpret-trailers --where after --trailer "CC: stakeholder@company.com"

# Add before existing trailers
git interpret-trailers --where before --trailer "Priority: urgent"

# Add at end of message
git interpret-trailers --where end --trailer "Signed-off-by: $(git config user.name)"

Integration with Git Workflows:

Commit Message Hook Integration:

.git/hooks/prepare-commit-msg

#!/bin/bash
# Add default trailers to commit message
git interpret-trailers --if-missing addIfMissing \
  --trailer "Signed-off-by: $(git config user.name) <$(git config user.email)>" \
  --in-place "$1"

Commit Template with Trailers:

# Create commit message template
cat > ~/.git-commit-template << 'EOF'
<commit message>


# Trailers (automatically managed by interpret-trailers)

Issue: #
EOF

# Configure template
git config commit.template ~/.git-commit-template

Amending Commits with Trailers:

# Amend last commit to add trailer
git commit --amend --no-edit -s  # Adds Signed-off-by

# Or manually add specific trailer
git interpret-trailers --trailer "Fixes: #123" --in-place .git/COMMIT_EDITMSG
git commit --amend --file=.git/COMMIT_EDITMSG

Batch Trailer Processing:

# Process multiple commit messages
for msg_file in commit-msg-*.txt; do
    git interpret-trailers --trailer "Reviewed-by: $(git config user.name)" \
                          --in-place "$msg_file"
done

# Add trailers based on branch name
branch=$(git symbolic-ref --short HEAD)
if [[ $branch == feature/* ]]; then
    git interpret-trailers --trailer "Feature-ID: ${branch#feature/}" --in-place "$1"
fi

Parsing and Extraction:

Extract Only Trailers:

# Parse commit message and show only trailers
cat COMMIT_MSG | git interpret-trailers --only-trailers

# Extract specific trailer types
cat COMMIT_MSG | git interpret-trailers --only-trailers | grep "^Fixes:"

Remove Trailers:

# Strip all trailers from message
cat COMMIT_MSG | git interpret-trailers --only-input

# Clean up empty trailer lines
git interpret-trailers --trim-empty --in-place COMMIT_MSG

Query Trailer Values:

# Check if trailer exists
git interpret-trailers --only-trailers < COMMIT_MSG | grep -q "Signed-off-by:" || echo "Missing signoff"

# Extract trailer value
fixes_id=$(cat COMMIT_MSG | git interpret-trailers --only-trailers | grep "^Fixes:" | sed 's/Fixes: *//')

Advanced Configurations:

Custom Trailer Definitions:

# Define custom trailer tokens
git config trailer.sign.key "Signed-off-by"
git config trailer.ack.key "Acked-by"
git config trailer.review.key "Reviewed-by"

# Configure trailer behavior
git config trailer.sign.ifexists "addIfDifferentNeighbor"
git config trailer.ack.where "after"

Integration Scripts:

Release Management:

#!/bin/bash
# Generate release notes from trailers
git log --oneline --grep="release\|tag" | while read hash msg; do
    if git show --no-patch --format="%B" $hash | git interpret-trailers --only-trailers | grep -q "Release:"; then
        release_info=$(git show --no-patch --format="%B" $hash | git interpret-trailers --only-trailers | grep "^Release:")
        echo "$hash: $msg - $release_info"
    fi
done

Issue Tracking Integration:

#!/bin/bash
# Extract issue IDs from commits and update issue tracker
git log --oneline | while read hash msg; do
    issue_ids=$(git show --no-patch --format="%B" $hash | git interpret-trailers --only-trailers | grep -o "#[0-9]\+" | tr '\n' ' ')
    if [ -n "$issue_ids" ]; then
        echo "Commit $hash fixes issues: $issue_ids"
        # Integrate with issue tracker API
    fi
done

CI/CD Integration:

#!/bin/bash
# Validate commit trailers in CI
if ! git interpret-trailers --only-trailers < "$COMMIT_MSG" | grep -q "Signed-off-by:"; then
    echo "ERROR: Commit must be signed off"
    exit 1
fi

if ! git interpret-trailers --only-trailers < "$COMMIT_MSG" | grep -q "Co-authored-by:"; then
    echo "WARNING: Consider adding co-authors"
fi

Formatting and Standards:

Trailer Ordering Rules:

# Preferred trailer order (most to least important):
Bug: <bug_id>
Fixes: <commit_or_issue>
Reported-by: <person>
Tested-by: <person>
Reviewed-by: <person>
Acked-by: <person>
Signed-off-by: <developer>

CC: <notification_list>

Multi-line Trailer Handling:

# Handle trailers that span multiple lines
git interpret-trailers --trailer "Description: This is a long
description that spans multiple lines" --in-place MSG

# Results in properly formatted multi-line trailer
Description: This is a long
 description that spans multiple lines

Troubleshooting Common Issues:

Trailer Not Appearing:

# Check message format
cat COMMIT_MSG | git interpret-trailers --verbose

# Debug trailer detection
git interpret-trailers --trailer "Debug: test" --in-place COMMIT_MSG
cat COMMIT_MSG  # Should show trailer

Conflicting Conditions:

# Use --if-exists and --if-missing wisely
git interpret-trailers --if-exists doNothing --if-missing add --trailer "Signed-off-by: Dev"
# Won't add if exists, will add if missing

Encoding and Formatting:

# Handle special characters in trailers
git interpret-trailers --trailer "Co-authored-by: José María <jm@example.com>"

# Preserve line endings
dos2unix COMMIT_MSG || true  # Ensure consistent line endings
git interpret-trailers --trailer "Status: ready" --in-place COMMIT_MSG

Performance with Large Messages:

# For very large commit messages, process sections
head -50 COMMIT_MSG > temp_msg
git interpret-trailers --in-place temp_msg
tail -n +51 COMMIT_MSG >> temp_msg
mv temp_msg COMMIT_MSG

Caution

interpret-trailers modifies commit messages. Test with sample files before applying to actual commits. Trailer order can affect meaning - follow project conventions.

Real-World Usage Examples:

Corporate Development Workflow:

.git/hooks/prepare-commit-msg

# Pre-commit hook for compliance trailers
#!/bin/bash
# Add required organizational trailers
org_name=$(git config user.organization)
user_email=$(git config user.email)

git interpret-trailers --if-missing add \
  --trailer "Organization: $org_name" \
  --trailer "Committer-Email: $user_email" \
  --in-place "$1"

# Add default CC
git interpret-trailers --if-missing add \
  --trailer "CC: team-lead@company.com" \
  --in-place "$1"

Open Source Contribution Standards:

.git/hooks/commit-msg

# Commit-msg hook to enforce project standards
#!/bin/bash
MSG_FILE=$1

# Check for required trailers
if ! git interpret-trailers --only-trailers < "$MSG_FILE" | grep -q "Signed-off-by:"; then
    echo "ERROR: Commit must include Signed-off-by trailer"
    echo "Run: git commit --amend --signoff"
    exit 1
fi

if ! git interpret-trailers --only-input < "$MSG_FILE" | grep -q "^[A-Z].*[.!?]$"; then
    echo "WARNING: Commit message should start with capital letter and end with punctuation"
fi

Automatic Bug Tracking:

.git/hooks/post-commit

# Post-commit hook to update bug tracker
#!/bin/bash
commit_msg=$(git show --no-patch --format=%B HEAD)

# Extract issue references
issues=$(echo "$commit_msg" | git interpret-trailers --only-trailers | \
         grep -E "^(Fixes|Bug|Issue|Closes):" | \
         grep -oE "#[0-9]+" | tr '\n' ',' | sed 's/,$//')

if [ -n "$issues" ]; then
    # Update bug tracking system
    curl -X POST "https://bugs.example.com/api/update" \
         -d "commit=$(git rev-parse HEAD)" \
         -d "status=fixed" \
         -d "issues=$issues"
fi

Tip

Use —in-place for safety with files. Combine conditions logically (if-exists with if-missing). Test trailer workflows with git commit —amend.

How are trailers different from regular commit message content?

Trailers use structured format with specific tokens and separators, occurring at message end after blank line, parseable by interpret-trailers for automated processing.

Can trailers be modified after commit creation?

Yes, amend commits to add/modify trailers: git commit —amend with updated message, or use interpret-trailers on commit message file.

What’s the difference between token: value and token # value formats?

Both valid; colon format is Git standard, hash format used in some email systems. interpret-trailers recognizes both but normalizes internally.

Can multiple instances of same trailer exist?

Supported - e.g., multiple Signed-off-by trailers for different contributors, multiple CC entries for different stakeholders.

How do trailers interact with git log formatting?

git log recognizes trailers for display; —format includes %(trailers) specifier. Tools can extract trailer data separately from main message.

Can trailers span multiple lines?

Yes, continuation lines start with space/tab after initial trailer line. interpret-trailers preserves multi-line trailer structure.

What’s the relationship between trailers and email patch workflows?

Trailers originally designed for email patches (like Signed-off-by); now used in direct commits. git format-patch maintains trailers in emailed patches.

How do trailers work with merge commits?

Merge commits support trailers; —signoff adds Signed-off-by to merge commit. Trailers can indicate merge approval and authorship.

Can trailers reference other commits?

Yes, Fixes:, Bug: trailers often reference commit hashes or issue IDs pointing to related changes or problems.

How do trailers interact with git rebase?

Rebase processes commit messages, trailers preserved unless explicitly modified. Can add —no-signoff to rebase to drop signoffs.

Can custom trailer tokens be defined?

No formal registration needed - any token: value format works. Projects establish conventions through documentation and hooks.

How do trailers help with compliance and auditing?

Structured metadata enables automated compliance checking, change tracking, and audit trails for regulatory requirements.

What’s the performance impact of trailer processing?

Negligible for typical commit messages; only becomes significant with very large messages or complex trailer processing in hooks.

Applications of the git interpret-trailers command

1. Contributor Management: Automated Signed-off-by trailer addition for developer workflow compliance
2. Issue Tracking Integration: Structured Fixes: and Closes: trailers linking commits to project issues
3. Code Review Workflows: Reviewed-by and Acked-by trailers documenting approval processes
4. Compliance Automation: Mandatory organizational trailers for regulatory and quality requirements
5. Change Attribution: Co-authored-by trailers for proper credit in collaborative projects
6. Workflow Automation: Scripts parsing trailers to trigger deployments, notifications, and integrations