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Top Forums Shell Programming and Scripting getting full path from relative path Post 302110800 by Perderabo on Thursday 15th of March 2007 11:29:37 AM
Old 03-15-2007
Suppose that I don't have room in /usr for /usr/local but I do have some room in /export. So I make a directory called /export/usr.local and it has a subdirectory called bin. And I do a "ln -s /export/usr.local /usr/local". Now I do a "cd /usr/local" then I do a "cd bin". At this point my view is that I am in /usr/local/bin and a shell with a built-in pwd command may return that path. But /usr/bin/pwd will return /export/usr.local/bin. With more symbolic links in a path, there can be more aliases like this. The value returned by /usr/bin/pwd is the physical path. With good permissions on each directory leading to the current directory, /usr/bin/pwd can return the physical path. A built-in pwd in the same shell that navigated to the current directory may be able to return the particular logical path used to arrive at the current directory. Finding all logical paths to a particular directory would be rather daunting.

Writing a program like /usr/bin/pwd is not very easy in unix. You can stat the . directory to get the inode of the current directory. Then you can open .. and stat each file in the parent directory until you find the same inode. You walk up the chain one .. at a time repeating this process until . and .. are the same inode which means you have reached /. (Actually it is harder than that because you might traverse a mount point.) This is why putting an NFS mounted filesystem in / is very unwise... every /usr/bin/pwd must contact the NFS server to perform the stat.
 

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Template::Plugin::File(3)				User Contributed Perl Documentation				 Template::Plugin::File(3)

NAME
Template::Plugin::File - Plugin providing information about files SYNOPSIS
[% USE File(filepath) %] [% File.path %] # full path [% File.name %] # filename [% File.dir %] # directory DESCRIPTION
This plugin provides an abstraction of a file. It can be used to fetch details about files from the file system, or to represent abstract files (e.g. when creating an index page) that may or may not exist on a file system. A file name or path should be specified as a constructor argument. e.g. [% USE File('foo.html') %] [% USE File('foo/bar/baz.html') %] [% USE File('/foo/bar/baz.html') %] The file should exist on the current file system (unless "nostat" option set, see below) as an absolute file when specified with as leading '"/"' as per '"/foo/bar/baz.html"', or otherwise as one relative to the current working directory. The constructor performs a "stat()" on the file and makes the 13 elements returned available as the plugin items: dev ino mode nlink uid gid rdev size atime mtime ctime blksize blocks e.g. [% USE File('/foo/bar/baz.html') %] [% File.mtime %] [% File.mode %] ... In addition, the "user" and "group" items are set to contain the user and group names as returned by calls to "getpwuid()" and "getgrgid()" for the file "uid" and "gid" elements, respectively. On Win32 platforms on which "getpwuid()" and "getgrid()" are not available, these values are undefined. [% USE File('/tmp/foo.html') %] [% File.uid %] # e.g. 500 [% File.user %] # e.g. abw This user/group lookup can be disabled by setting the "noid" option. [% USE File('/tmp/foo.html', noid=1) %] [% File.uid %] # e.g. 500 [% File.user %] # nothing The "isdir" flag will be set if the file is a directory. [% USE File('/tmp') %] [% File.isdir %] # 1 If the "stat()" on the file fails (e.g. file doesn't exists, bad permission, etc) then the constructor will throw a "File" exception. This can be caught within a "TRY...CATCH" block. [% TRY %] [% USE File('/tmp/myfile') %] File exists! [% CATCH File %] File error: [% error.info %] [% END %] Note the capitalisation of the exception type, '"File"', to indicate an error thrown by the "File" plugin, to distinguish it from a regular "file" exception thrown by the Template Toolkit. Note that the "File" plugin can also be referenced by the lower case name '"file"'. However, exceptions are always thrown of the "File" type, regardless of the capitalisation of the plugin named used. [% USE file('foo.html') %] [% file.mtime %] As with any other Template Toolkit plugin, an alternate name can be specified for the object created. [% USE foo = file('foo.html') %] [% foo.mtime %] The "nostat" option can be specified to prevent the plugin constructor from performing a "stat()" on the file specified. In this case, the file does not have to exist in the file system, no attempt will be made to verify that it does, and no error will be thrown if it doesn't. The entries for the items usually returned by "stat()" will be set empty. [% USE file('/some/where/over/the/rainbow.html', nostat=1) [% file.mtime %] # nothing METHODS
All "File" plugins, regardless of the "nostat" option, have set a number of items relating to the original path specified. path The full, original file path specified to the constructor. [% USE file('/foo/bar.html') %] [% file.path %] # /foo/bar.html name The name of the file without any leading directories. [% USE file('/foo/bar.html') %] [% file.name %] # bar.html dir The directory element of the path with the filename removed. [% USE file('/foo/bar.html') %] [% file.name %] # /foo ext The file extension, if any, appearing at the end of the path following a '"."' (not included in the extension). [% USE file('/foo/bar.html') %] [% file.ext %] # html home This contains a string of the form '"../.."' to represent the upward path from a file to its root directory. [% USE file('bar.html') %] [% file.home %] # nothing [% USE file('foo/bar.html') %] [% file.home %] # .. [% USE file('foo/bar/baz.html') %] [% file.home %] # ../.. root The "root" item can be specified as a constructor argument, indicating a root directory in which the named file resides. This is otherwise set empty. [% USE file('foo/bar.html', root='/tmp') %] [% file.root %] # /tmp abs This returns the absolute file path by constructing a path from the "root" and "path" options. [% USE file('foo/bar.html', root='/tmp') %] [% file.path %] # foo/bar.html [% file.root %] # /tmp [% file.abs %] # /tmp/foo/bar.html rel(path) This returns a relative path from the current file to another path specified as an argument. It is constructed by appending the path to the '"home"' item. [% USE file('foo/bar/baz.html') %] [% file.rel('wiz/waz.html') %] # ../../wiz/waz.html EXAMPLES
[% USE file('/foo/bar/baz.html') %] [% file.path %] # /foo/bar/baz.html [% file.dir %] # /foo/bar [% file.name %] # baz.html [% file.home %] # ../.. [% file.root %] # '' [% file.abs %] # /foo/bar/baz.html [% file.ext %] # html [% file.mtime %] # 987654321 [% file.atime %] # 987654321 [% file.uid %] # 500 [% file.user %] # abw [% USE file('foo.html') %] [% file.path %] # foo.html [% file.dir %] # '' [% file.name %] # foo.html [% file.root %] # '' [% file.home %] # '' [% file.abs %] # foo.html [% USE file('foo/bar/baz.html') %] [% file.path %] # foo/bar/baz.html [% file.dir %] # foo/bar [% file.name %] # baz.html [% file.root %] # '' [% file.home %] # ../.. [% file.abs %] # foo/bar/baz.html [% USE file('foo/bar/baz.html', root='/tmp') %] [% file.path %] # foo/bar/baz.html [% file.dir %] # foo/bar [% file.name %] # baz.html [% file.root %] # /tmp [% file.home %] # ../.. [% file.abs %] # /tmp/foo/bar/baz.html # calculate other file paths relative to this file and its root [% USE file('foo/bar/baz.html', root => '/tmp/tt2') %] [% file.path('baz/qux.html') %] # ../../baz/qux.html [% file.dir('wiz/woz.html') %] # ../../wiz/woz.html AUTHORS
Michael Stevens wrote the original "Directory" plugin on which this is based. Andy Wardley split it into separate "File" and "Directory" plugins, added some extra code and documentation for "VIEW" support, and made a few other minor tweaks. COPYRIGHT
Copyright 2000-2007 Michael Stevens, Andy Wardley. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. SEE ALSO
Template::Plugin, Template::Plugin::Directory, Template::View perl v5.16.3 2011-12-20 Template::Plugin::File(3)
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