How to Output Draw.io XML to stdout using graphviz2drawio

Use the --stdout flag when running graphviz2drawio to print the generated Draw.io XML directly to standard output instead of writing to a file.

The hbmartin/graphviz2drawio repository converts GraphViz DOT diagrams into Draw.io-compatible XML format. While the default behavior saves output to a .drawio file, you can output the Draw.io XML to stdout using graphviz2drawio by passing the --stdout flag, enabling seamless integration with shell pipelines, environment variables, and automated workflows.

Using the --stdout Flag

The command-line interface provides the --stdout option to bypass file creation and stream the XML directly to your terminal.

Basic Syntax

To convert a single DOT file and print the XML to the terminal:

graphviz2drawio --stdout mygraph.dot

Piping from stdin

You can combine input redirection with stdout output by using the special filename -, which tells the tool to read GraphViz data from standard input:

cat mygraph.dot | graphviz2drawio --stdout -

Combining with Layout Engines

The -p (or --program) option works independently of output routing, allowing you to specify alternative GraphViz layout engines like neato, fdp, or circo while still printing to stdout:

graphviz2drawio -p neato --stdout mygraph.dot

Capturing Output in Shell Scripts

When automating diagram generation, you can capture the XML directly into a shell variable or pipe it to downstream tools without intermediate files:

#!/usr/bin/env bash

# Convert a DOT file and capture the XML into a variable

xml=$(graphviz2drawio --stdout diagram.dot)

# Send the XML to a web service or process it further

curl -X POST -d "$xml" https://example.com/upload

This pattern eliminates filesystem I/O overhead and keeps sensitive diagrams in memory only.

Technical Implementation Details

The stdout behavior is controlled by three coordinated components in the codebase.

CLI Argument Definition

In graphviz2drawio/models/Arguments.py, the parser defines the --stdout flag that sets the corresponding attribute in the arguments namespace.

Output Decision Logic

In graphviz2drawio/__main__.py, the helper function _determine_single_output inspects the parsed arguments. When --stdout is detected, it returns [None] to signal that no output file path should be generated.

XML Generation and Printing

The _convert_file function in graphviz2drawio/__main__.py calls the core convert() function from graphviz2drawio/graphviz2drawio.py. This function orchestrates the conversion pipeline:

• graphviz2drawio/models/SvgParser.py parses the SVG output from GraphViz into internal node and edge representations
• graphviz2drawio/mx/MxGraph.py constructs the MX Graph model that matches Draw.io's format
• The convert() function returns the final XML string

When the outfile parameter is None (as determined by _determine_single_output), the CLI wrapper executes print(output), sending the Draw.io XML directly to stdout.

Summary

• The --stdout flag directs XML output to the terminal instead of creating a .drawio file
• Use - as the input filename to read DOT data from stdin while writing to stdout
• The _determine_single_output helper in __main__.py returns [None] to signal stdout-only mode
• When outfile is None, the conversion wrapper executes print(output) to emit the XML string

Frequently Asked Questions

Can I pipe a DOT file into graphviz2drawio and get XML on stdout?

Yes. Use the special filename - to read from stdin combined with the --stdout flag: cat diagram.dot | graphviz2drawio --stdout -. This processes the piped input and prints the resulting Draw.io XML to your terminal.

Does the --stdout flag work with alternative layout engines like neato or fdp?

Yes. The -p (or --program) option is independent of output routing. You can specify any GraphViz layout engine while still printing to stdout: graphviz2drawio -p fdp --stdout diagram.dot.

How do I capture the Draw.io XML output into a shell variable?

Use command substitution to store the XML in a variable: xml=$(graphviz2drawio --stdout diagram.dot). The variable now contains the complete XML string, allowing you to manipulate it without creating temporary files.

What happens if I omit the --stdout flag?

Without --stdout, graphviz2drawio writes the XML to a file named after the input file with a .drawio extension (e.g., diagram.dot becomes diagram.drawio) and prints the filepath to stdout instead of the XML content.

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    "instagit": {
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}