Cygwin Shims Generator

Cygwin, like any other Unix system, installs executables to global binary directories (/usr/bin). It is useful to be able to export specific binaries from bin to the Command Processor and PowerShell, but without exporting the entire bin directory.

This project provides a tiny C launcher which can be used to create shim executables for invoking Cygwin programs. It sets up the environment to allow them to be called without realising that they are not running from a Cygwin shell.

These shims can be put in a different directory which can be added to PATH, allowing them to be used without pulling in the whole of Cygwin's bin directory.

Compilation

See gen_config.sh. The shim executable is compiled with:

$ x86_64-w64-mingw32-gcc '-DCYGWIN_ROOT=C:\cygwin64' -DUNICODE -nostdlib -Os \
                         -Wl,-entry=shim -o shim.exe shim.c -lkernel32

(if compiling for 32-bit, the entry point will be _shim)

shim.exe can then be renamed or copied and, when run, will attempt to execute its own basename from the bin directory under CYGWIN_ROOT, passing all the same arguments except that the first argument (i.e. argv[0]) will be rewritten to the correct executable path.

Note that while shim.exe can be hard-linked to new names, symlinks fail since Cygwin's resolution of basename causes the file to have the wrong basename when invoked from within a Cygwin shell (i.e. a symlinked executable will work outside Cygwin, but not inside it).

opam package

gen_config.sh is intended for use in opam-repository, but it compiles shim.c and generates opam .config and .install files.

The mingw-w64-shims package requires one of the mingw-w64 C compilers and uses cygcheck to install a copy of shim.exe for each binary installed by the mingw-w64 packages which are wrapped in opam-repository.

The package also ensure that the mingw-w64 runtime bin directory is added to PATH.