Differences between MSYS2 and Cygwin
Traditionally MSYS bash has been considered inferior to Cygwin bash. The former was an ancillary tool inside MinGW intended for running autoconf scripts. But now there is MinGW-w64 and MSYS2. The latter ships with a sweet pacman like package manager and elegant shells like zsh, so I wonder if there is still a gap in the emulation layer.
While MinGW* applications are Windows native executables, MSYS2 software requires a POSIX-emulation layer, just like Cygwin does. At least to a casual user, it is hard to spot the differences between the two.
- Which are the functional differences between the two emulation layers (if any)?
- Which emulation is faster (more efficient)?
Answer
Traditionally MSYS bash has been inferior, but mostly because Cygwin remained under active development whereas MSYS didn't. MSYS forked from Cygwin version 1.3.3 and never re-synced, whereas MSYS2 resyncs with the Cygwin project regularly.
We don't have a "sweet pacman like package manager", we have as direct a re-compilation of Arch Linux's pacman package manager as we could achieve.
MSYS2 doesn't have cygwin.dll but it does have msys-2.0.dll which does the same thing (and some more besides). Specifically, arguments that look like paths and the PATH env. var are converted to Windows form when running Windows-native software.
As for whether it's slower, I expect there'd be very little difference but MSYS2 would be a tiny amount slower due to the extra conversion work. Then again, chances are you'll run more Windows-native software from within MSYS2 (such as MinGW-w64 compilers) than you would from Cygwin so that'll shift things back in MSYS2's favour.