Windows filenames invalid under Windows are also invalid under Cygwin. This means that base filenames such as AUX, COM1, LPT1 or PRN (to name a few) cannot be used in a regular Cygwin Windows or POSIX path, even with an extension (prn.txt). However the special names can be used as filename extensions (file.aux). You can use the special names as you would under DOS, for example you can print on your default printer with the command cat filename > PRN (make sure to end with a Form Feed).

There is no need to create a POSIX /dev directory as Cygwin automatically simulates it internally. These devices cannot be seen with the command ls /dev/ although commands such as ls /dev/tty work fine. If you want to be able to see all devices in /dev/, you can use Igor Pechtchanski's create_devices.sh script.

Cygwin supports the following devices commonly found on POSIX systems: /dev/dsp, /dev/null, /dev/zero, /dev/console, /dev/tty, /dev/ttym, /dev/ttyX, /dev/ttySX, /dev/pipe, /dev/port, /dev/ptmx, /dev/mem, /dev/random, and /dev/urandom. Some other POSIX devices, such as /dev/kmem, are planned for development. Cygwin also has several Windows-specific devices: /dev/comX (the serial ports, starting with COM1 which is the same as ttyS0), /dev/conin (Windows CONIN$), /dev/conout (Windows CONOUT$), /dev/clipboard (the Windows clipboard, currently text only), and /dev/windows (the Windows message queue).

Windows NT/W2K/XP additionally support raw devices like floppies, disks, partitions and tapes. These are accessed from Cygwin applications using POSIX device names which are supported in two different ways.

Up to Cygwin 1.3.3 the only way to access those devices was to mount the Win32 device names to a POSIX device name but this usage is discouraged since Cygwin 1.3.4 and only kept for backward compatibility.

Beginning with Cygwin 1.3.4, raw devices are accessible by Cygwin processes using fixed POSIX device names. These fixed POSIX device names are generated using a direct conversion from the POSIX namespace to the internal NT namespace. E.g. the first harddisk is the NT internal device \device\harddisk0\partition0 or the first partition on the third harddisk is \device\harddisk2\partition1. The first floppy in the system is \device\floppy0, the first CD-ROM is \device\cdrom0 and the first tape drive is \device\tape0.

The new fixed POSIX names are mapped to NT internal devices as follows:

/dev/st0	\device\tape0, rewind
/dev/nst0	\device\tape0, no-rewind
/dev/st1	\device\tape1
...

/dev/fd0	\device\floppy0
/dev/fd1	\device\floppy1
...

/dev/scd0	\device\cdrom0
/dev/scd1	\device\cdrom1
...

/dev/sr0	\device\cdrom0
/dev/sr1	\device\cdrom1
...

/dev/sda	\device\harddisk0\partition0	(whole disk)
/dev/sda1	\device\harddisk0\partition1	(first partition)
...
/dev/sda15	\device\harddisk0\partition15	(fifteenth partition)

/dev/sdb	\device\harddisk1\partition0
/dev/sdb1	\device\harddisk1\partition1

[up to]

/dev/sdl	\device\harddisk11\partition0
/dev/sdl1	\device\harddisk11\partition1
...
/dev/sdl15	\device\harddisk11\partition15

if you don't like these device names, feel free to create symbolic links as they are created on Linux systems for convenience:

ln -s /dev/scd0 /dev/cdrom
ln -s /dev/nst0  /dev/tape
...

mount -f -b /dev/nst0 /dev/tape     # DOES NOT WORK
mount -f -b /device/tape0 /dev/tape # DOES NOT WORK
ln -s /device/tape0 /dev/tape       # DOES NOT WORK

Executable program filenames end with .exe but the .exe need not be included in the command, so that traditional UNIX names can be used. However, for programs that end in .bat and .com, you cannot omit the extension.

As a side effect, the ls filename gives information about filename.exe if filename.exe exists and filename does not. In the same situation the function call stat("filename",..) gives information about filename.exe. The two files can be distinguished by examining their inodes, as demonstrated below.

C:\> ls * 
a      a.exe     b.exe
C:\> ls -i a a.exe
445885548 a       435996602 a.exe
C:\> ls -i b b.exe
432961010 b       432961010 b.exe

If a shell script myprog and a program myprog.exe coexist in a directory, the shell script has precedence and is selected for execution of myprog. Note that this was quite the reverse up to Cygwin 1.5.19. It has been changed for consistency with the rest of Cygwin.

The gcc compiler produces an executable named filename.exe when asked to produce filename. This allows many makefiles written for UNIX systems to work well under Cygwin.

Unfortunately, the install and strip commands do distinguish between filename and filename.exe. They fail when working on a non-existing filename even if filename.exe exists, thus breaking some makefiles. This problem can be solved by writing install and strip shell scripts to provide the extension ".exe" when needed.

Cygwin, like Linux and other similar operating systems, supports the /proc virtual filesystem. The files in this directory are representations of various aspects of your system, for example the command cat /proc/cpuinfo displays information such as what model and speed processor you have.

One unique aspect of the Cygwin /proc filesystem is /proc/registry, which displays the Windows registry with each KEY as a directory and each VALUE as a file. As anytime you deal with the Windows registry, use caution since changes may result in an unstable or broken system.

The Cygwin /proc is not as complete as the one in Linux, but it provides significant capabilities. The procps package contains several utilities that use it.

To circumvent the limitations on shell line length in the native Windows command shells, Cygwin programs expand their arguments starting with "@" in a special way. If a file pathname exists, the argument @pathname expands recursively to the content of pathname. Double quotes can be used inside the file to delimit strings containing blank space. Embedded double quotes must be repeated. In the following example compare the behaviors of the bash built-in echo and of the program /bin/echo.

bash$ echo  'This   is   "a     long"  line' > mylist
bash$ echo @mylist
@mylist
c:\> c:\cygwin\bin\echo @mylist
This is a     long line