Does the Instagit CLI Support Standard Input (STDIN)?

Yes, the Instagit CLI supports reading DESIGN.md documents from standard input by passing - (hyphen) as the file argument to any command.

The Instagit CLI, part of the google-labs-code/design.md repository, provides robust support for Unix-style piping workflows. According to the source code, every command that processes DESIGN.md files can accept input from stdin instead of a file path, enabling seamless integration with shell pipelines and automated workflows.

How STDIN Support Is Implemented

The readInput Utility Function

The core stdin handling logic resides in the readInput function located in packages/cli/src/utils.ts at lines 18-28. This utility checks whether the supplied file path equals the string "-", and when it detects this special character, it consumes the entire stream from process.stdin rather than reading from the filesystem.

According to the implementation in packages/cli/src/utils.ts, the function treats the hyphen as a signal to switch input sources, making it possible to pipe content directly into the tool without writing temporary files.

Command-Level STDIN Integration

All Instagit CLI commands that expect a DESIGN.md file explicitly document this behavior in their argument descriptions. For example:

• In packages/cli/src/commands/lint.ts at line 27, the positional argument is described as "Path to DESIGN.md (use - for stdin)"
• In packages/cli/src/commands/export.ts at line 31, the same documentation pattern appears

The top-level README.md at line 219 confirms this capability, stating that "All commands accept a file path or - for stdin".

Practical Usage Examples

Standard File Input

instagit lint path/to/DESIGN.md

Piping from STDIN

cat path/to/DESIGN.md | instagit lint -

Git Integration Pipeline

git show HEAD:DESIGN.md | instagit export - --format=json

All examples work because the readInput function in packages/cli/src/utils.ts (lines 21-28) automatically detects the - argument and reads from process.stdin.

Summary

• The readInput function in packages/cli/src/utils.ts provides centralized stdin handling when the file argument is -
• All Instagit CLI commands support stdin input for DESIGN.md files, as documented in the README.md at line 219
• The lint and export commands in packages/cli/src/commands/ explicitly declare this capability in their argument descriptions
• Shell pipelines like cat design.md | instagit lint - work natively without additional flags

Frequently Asked Questions

How do I use stdin with the Instagit CLI?

Pass - (hyphen) as the file path argument. The readInput utility in packages/cli/src/utils.ts detects this character and reads the entire stream from process.stdin instead of the filesystem. For example: cat design.md | instagit lint -.

Which commands support reading from stdin?

All commands that accept a DESIGN.md file path support stdin input, including lint and export. The argument descriptions in packages/cli/src/commands/lint.ts and packages/cli/src/commands/export.ts explicitly document this behavior for users.

Is there a specific flag required for stdin mode?

No special flag is needed. Simply use - as the file argument. The CLI automatically switches to stdin mode when it encounters this character, as implemented in the readInput function at lines 18-28 of packages/cli/src/utils.ts.

Where is the stdin handling logic implemented?

The logic resides in the readInput function within packages/cli/src/utils.ts (lines 18-28). This function checks if the input path equals "-" and conditionally reads from process.stdin rather than loading a file from disk.

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}