MachO binaries contain load commands to indicate to dyld where it should search for the libraries the binary depends on.

These paths are often useful to inspect when debugging why your binary isn't discovering the libraries you'd expect.

Previously you could discover these with:

% otool -l `xcrun -f swiftc` \
  | grep -A2 LC_RPATH \
  | grep "^\s*path" \
  | cut -d " " -f 11
@executable_path/../lib/swift/macosx
@executable_path/../lib/swift/macosx

This example is quite verbose and fragile for such a common action, so recently I committed a change to add an easier option with LLVM's objdump. This change shipped with LLVM 13 or Xcode 13.3 on macOS, allowing you to run:

% objdump --macho --rpaths `xcrun -f swiftc`
/Applications/Xcode-13.3.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc:
@executable_path/../lib/swift/macosx

This is much more succinct and memorable, but also has slightly different output. This is because objdump automatically detects the current machine's architecture, and only prints the rpaths for that slice of the fat binary. It also outputs the path of the binary being run on, which you can disable with --no-leading-headers.

Hopefully you find this as useful as I do!