277 lines
12 KiB
Plaintext
277 lines
12 KiB
Plaintext
<sect1 id="using-pathnames"><title>Mapping path names</title>
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<sect2><title>Introduction</title>
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<para>Cygwin supports both Win32- and POSIX-style paths, where
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directory delimiters may be either forward or back slashes. UNC
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pathnames (starting with two slashes and a network name) are also
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supported.</para>
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<para>POSIX operating systems (such as Linux) do not have the concept
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of drive letters. Instead, all absolute paths begin with a
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slash (instead of a drive letter such as "c:") and all file systems
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appear as subdirectories (for example, you might buy a new disk and
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make it be the <filename>/disk2</filename> directory).</para>
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<para>Because many programs written to run on UNIX systems assume
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the existance of a single unified POSIX file system structure, Cygwin
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maintains a special internal POSIX view of the Win32 file system
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that allows these programs to successfully run under Windows. Cygwin
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uses this mapping to translate between Win32 and POSIX paths as
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necessary.</para>
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</sect2>
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<sect2 id="mount-table"><title>The Cygwin Mount Table</title>
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<para>The <command>mount</command> utility program is used to
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to map Win32 drives and network shares into Cygwin's internal POSIX
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directory tree. This is a similar concept to the typical UNIX mount
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program. For those people coming from a Windows background, the
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<command>mount</command> utility is very similar to the old DOS
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<command>join</command>, in that it makes your drive letters appear as
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subdirectories somewhere else.</para>
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<para>The mapping is stored in the current user's Cygwin
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<FirstTerm>mount table</FirstTerm> in the Windows registry so that the
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information will be retrieved next time the user logs in. Because it
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is sometimes desirable to have system-wide as well as user-specific
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mounts, there is also a system-wide mount table that all Cygwin users
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inherit. The system-wide table may only be modified by a user with
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the appropriate priviledges (Administrator priviledges in Windows
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NT).</para>
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<para>The current user's table is located under
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"HKEY_CURRENT_USER/Software/Cygnus Solutions/Cygwin/mounts
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v<version>"
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where <version> is the latest registry version associated with
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the Cygwin library (this version is not the same as the release
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number). The system-wide table is located under the same subkeys
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under HKEY_LOCAL_SYSTEM.</para>
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<para>By default, the POSIX root <filename>/</filename> points to the
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system partition but it can be relocated to any directory in the
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Windows file system using the <command>mount</command> command.
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Whenever Cygwin generates a POSIX path from a Win32 one, it uses the
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longest matching prefix in the mount table. Thus, if
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<filename>C:</filename> is mounted as <filename>/c</filename> and also
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as <filename>/</filename>, then Cygwin would translate
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<filename>C:/foo/bar</filename> to <filename>/c/foo/bar</filename>.</para>
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<para>Invoking <command>mount</command> without any arguments displays
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Cygwin's current set of mount points.
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In the following example, the C
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drive is the POSIX root and D drive is mapped to
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<filename>/d</filename>. Note that in this case, the root mount is a
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system-wide mount point that is visible to all users running Cygwin
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programs, whereas the <filename>/d</filename> mount is only visible
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to the current user.</para>
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<example>
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<title>Displaying the current set of mount points</title>
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<screen>
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<prompt>c:\cygnus\></prompt> <userinput>mount</userinput>
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Device Directory Type Flags
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D: /d user textmode
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C: / system textmode
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</screen>
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</example>
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<para>You can also use the <command>mount</command> command to add
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new mount points, and the <command>umount</command> to delete
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them. See <Xref Linkend="mount"> and <Xref Linkend="umount"> for more
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information on how to use these utilities to set up your Cygwin POSIX
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file system.</para>
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<para>Whenever Cygwin cannot use any of the existing mounts to convert
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from a particular Win32 path to a POSIX one, Cygwin will
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automatically default to an imaginary mount point under the default POSIX
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path <filename>/cygdrive</filename>. For example, if Cygwin accesses
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<filename>Z:\foo</filename> and the Z drive is not currently in the
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mount table, then <filename>Z:\</filename> would be automatically
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converted to <filename>/cygdrive/Z</filename>. The default
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prefix of <filename>/cygdrive</filename> may be changed (see the
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<Xref Linkend="mount"> for more information).</para>
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<para>It is possible to assign some special attributes to each mount
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point. Automatically mounted partitions are displayed as "auto"
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mounts. Mounts can also be marked as either "textmode" or "binmode"
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-- whether text files are read in the same manner as binary files by
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default or not (see <Xref Linkend="using-textbinary"> for more
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information on text and binary modes.</para>
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</sect2>
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<sect2><title>Cygwin Mount Table Strategies</title>
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<para>Which set of mounts is right for a given Cygwin user depends
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largely on how closely you want to simulate a POSIX environment,
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whether you mix Windows and Cygwin programs, and how many drive
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letters you are using. If you want to be very POSIX-like (assuming
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"CygwinRoot" is the top directory of your Cygwin distribution), you may
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want to do something like this:</para>
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<example><title>POSIX-like mount setup</title>
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<screen>
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<prompt>C:\></prompt> <userinput>mount c:\Cygnus\CygwinRoot /</userinput>
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<prompt>C:\></prompt> <userinput>mount c:\ /c</userinput>
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<prompt>C:\></prompt> <userinput>mount d:\ /d</userinput>
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<prompt>C:\></prompt> <userinput>mount e:\ /cdrom</userinput>
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</screen>
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</example>
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<para>However, if you mix Windows and Cygwin programs a lot, you might
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want to create an "identity" mapping, so that conversions between the
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two (see <Xref Linkend="cygpath">) can be eliminated:</para>
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<example><title>Identity mount setup</title>
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<screen>
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<prompt>C:\></prompt> <userinput>mount c:\ \</userinput>
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<prompt>C:\></prompt> <userinput>mount d:\foo /foo</userinput>
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<prompt>C:\></prompt> <userinput>mount d:\bar /bar</userinput>
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<prompt>C:\></prompt> <userinput>mount e:\grill /grill</userinput>
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</screen>
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</example>
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<para>You'd have to repeat this for all top-level subdirectories on
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all drives, but then you'd always have the top-level directories
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available as the same names in both systems.</para>
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</sect2>
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<sect2><title>Additional Path-related Information</title>
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<para>The <command>cygpath</command> program provides the ability to
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translate between Win32 and POSIX pathnames in shell scripts. See
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<Xref Linkend="cygpath"> for the details.</para>
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<para>The <EnVar>HOME</EnVar>, <EnVar>PATH</EnVar>, and
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<EnVar>LD_LIBRARY_PATH</EnVar> environment variables are automatically
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converted from Win32 format to POSIX format (e.g. from
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<filename>C:\cygnus\cygwin-b20\H-i586-cygwin32\bin</filename> to
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<filename>/bin</filename>, if there was a mount from that Win32 path to
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that POSIX path) when a Cygwin process first starts.</para>
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<para>Symbolic links can also be used to map Win32 pathnames to POSIX.
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For example, the command
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<command>ln -s //pollux/home/joe/data /data</command> would have about
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the same effect as creating a mount point from
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<filename>//pollux/home/joe/data</filename> to <filename>/data</filename>
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using <command>mount</command>, except that symbolic links cannot set
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the default file access mode. Other differences are that the mapping is
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distributed throughout the file system and proceeds by iteratively
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walking the directory tree instead of matching the longest prefix in a
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kernel table. Note that symbolic links will only work on network
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drives that are properly configured to support the "system" file
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attribute. Many do not do so by default (the Unix Samba server does
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not by default, for example).</para>
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</sect2>
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</sect1>
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<sect1 id="using-specialnames"><title>Special filenames</title>
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<sect2> <title>DOS devices</title>
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<para>Windows filenames invalid under Windows are also invalid under
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Cygwin. This means that base filenames such as
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<filename>AUX</filename>, <filename>COM1</filename>,
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<filename>LPT1</filename> or <filename>PRN</filename> (to name a few)
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cannot be used in a regular Cygwin Windows or POSIX path, even with an
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extension (<filename>prn.txt</filename>). However the special names can be
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used as filename extensions (<filename>file.aux</filename>). You can use
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the special names as you would under DOS, for example you can print on your
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default printer with the command <command>cat filename > PRN</command>
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(make sure to end with a Form Feed).
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</para>
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</sect2>
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<sect2> <Title>POSIX devices</title>
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<para>There is no need to create a POSIX <filename>/dev</filename>
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directory as it is simulated within Cygwin automatically.
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It supports the following devices: <filename>/dev/null</filename>,
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<filename>/dev/tty</filename> and
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<filename>/dev/comX</filename> (the serial ports).
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These devices cannot be seen with the command <command>ls /dev</command>
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although commands such as <command>ls /dev/tty</command> work fine.
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<comment>
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FIXME: Are there other devices under /dev. What about the funny ones
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mounted by default, such as /dev/fd1. What do they really do?
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</comment>
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</para>
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</sect2>
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<sect2><title>The .exe extension</title>
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<para> Executable program filenames end with .exe but the .exe need
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not be included in the command, so that traditional UNIX names can be
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used. However, for programs that end in ".bat" and ".com", you cannot
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omit the extension.
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</para>
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<para>As a side effect, the <command> ls filename</command> gives
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information about <filename>filename.exe</filename> if
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<filename>filename.exe</filename> exists and <filename>filename</filename>
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does not. In the same situation the function call
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<function>stat("filename",..)</function> gives information about
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<filename>filename.exe</filename>. The two files can be distinguished
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by examining their inodes, as demonstrated below.
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<screen>
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<prompt>C:\Cygnus\></prompt> <userinput>ls * </userinput>
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a a.exe b.exe
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<prompt>C:\Cygnus\></prompt> <userinput>ls -i a a.exe</userinput>
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445885548 a 435996602 a.exe
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<prompt>C:\Cygnus\></prompt> <userinput>ls -i b b.exe</userinput>
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432961010 b 432961010 b.exe
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</screen>
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If a shell script <filename>myprog</filename> and a program
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<filename>myprog.exe</filename> coexist in a directory, the program
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has precedence and is selected for execution of
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<command>myprog</command>.</para>
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<para>The <command>gcc</command> compiler produces an executable named
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<filename>filename.exe</filename> when asked to produce
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<filename>filename</filename>. This allows many makefiles written
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for UNIX systems to work well under Cygwin.</para>
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<para>Unfortunately, the <command>install</command> and
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<command>strip</command> commands do distinguish between
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<filename>filename</filename> and <filename>filename.exe</filename>. They
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fail when working on a non-existing <filename>filename</filename> even if
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<filename>filename.exe</filename> exists, thus breaking some makefiles.
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This problem can be solved by writing <command>install</command> and
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<command>strip</command> shell scripts to provide the extension ".exe"
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when needed.
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</para>
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</sect2>
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<sect2><title>The @pathnames</title>
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<para>To circumvent the limitations on shell line length in the native
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Windows command shells, Cygwin programs expand their arguments
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starting with "@" in a special way. If a file
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<filename>pathname</filename> exists, the argument
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<filename>@pathname</filename> expands recursively to the content of
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<filename>pathname</filename>. Double quotes can be used inside the
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file to delimit strings containing blank space.
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Embedded double quotes must be repeated.
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In the following example compare the behaviors of the bash built-in
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<command>echo</command> and of the program <command>/bin/echo</command>.</para>
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<example><title> Using @pathname</title>
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<screen>
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<prompt>/Cygnus$</prompt> <userinput>echo 'This is "a long" line' > mylist</userinput>
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<prompt>/Cygnus$</prompt> <userinput>echo @mylist</userinput>
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@mylist
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<prompt>/Cygnus$</prompt> <userinput>/bin/echo @mylist</userinput>
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This is a long line
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<prompt>/Cygnus$</prompt> <userinput>rm mylist</userinput>
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<prompt>/Cygnus$</prompt> <userinput>/bin/echo @mylist</userinput>
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@mylist
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</screen>
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</example>
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</sect2>
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</sect1>
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