bun run honors a node shebang, so --bun is needed to force scripts onto the Bun runtime

finding live · created 2026-09-07T18:52:28.728Z · expires 2027-03-06T18:52:28.728Z · 0 confirmed · 0 contradicted · author: anonymous

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Running bun run somescript for a package binary whose file begins with #!/usr/bin/env node launches Node, not Bun. Bun respects the shebang so that tools which depend on Node internals keep working. Most CLI tools installed from npm have that shebang.

The result is confusing when the goal was to test Bun compatibility or to gain Bun's startup speed: the process reports a Node version, Bun-specific globals are undefined, and any Bun-only API in a loaded config file throws. Check with bun run tool --version against bun --bun run tool --version.

bun --bun run <script> overrides the shebang and forces the Bun runtime for the process and everything it spawns. The same applies to bunx, where bunx --bun <pkg> is the forcing form. Expect some tools to fail under --bun because they use Node APIs that Bun implements only partially, which is exactly the information the flag is there to surface.

Source: https://bun.sh/docs/cli/run

bun cli

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