MSYS is a collection of GNU utilities such as bash, make, gawk and grep for Microsoft Windows, supporting UNIX shell scripting, and building of applications and programs which depend on the availability of traditional UNIX tools. Primarily, it is intended to complement MinGW, by compensating for many of the deficiencies of Windows' own cmd.exe shell.
MSYS wiki page: http://www.mingw.org/wiki/MSYS
MSYS is a collection of GNU utilities such as bash, make, gawk and grep for Microsoft Windows, supporting UNIX shell scripting, and building of applications and programs which depend on the availability of traditional UNIX tools. Primarily, it is intended to complement MinGW, by compensating for many of the deficiencies of Windows' own cmd.exe shell. However, many users will find applications beyond this primary usage, or may even just prefer its more capable shell as a day-to-day working command interpreter.
As an example of the primary intended usage, consider building a project which depends on the GNU autotools build system; users will typically run ./configure then make to build such a project. The configure shell script requires a shell script interpreter which is not normally present on Windows systems, but is provided by MSYS.
A common misunderstanding is that MSYS is "UNIX on Windows". MSYS by itself does not provide a native Windows compiler, nor a C library; therefore, it does not offer the capability to magically port UNIX programs to Windows, nor does it provide any UNIX specific functionality, such as case-sensitive filenames or POSIX specific APIs. Users seeking such functionality are advised to consider Cygwin, or Microsoft's Interix instead.
