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Full Discussion: getting full path from relative path
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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LEARN ABOUT OPENSOLARIS

whereis

whereis(1B)					     SunOS/BSD Compatibility Package Commands					       whereis(1B)

NAME

       whereis - locate the binary, source, and manual page files for a command

SYNOPSIS

       /usr/ucb/whereis [-bmsu] [-BMS directory... -f] filename...

DESCRIPTION

       The  whereis utility locates source/binary and manuals sections for specified files. The supplied names are first stripped of leading path-
       name components and any (single) trailing extension of the form .ext, for example, .c. Prefixes of s. resulting from  use  of  source  code
       control are also dealt with. whereis then attempts to locate the desired program in a list of standard places:

	 etc
	 /sbin
	 /usr/bin
	 /usr/ccs/bin
	 /usr/ccs/lib
	 /usr/lang
	 /usr/lbin
	 /usr/lib
	 /usr/sbin
	 /usr/ucb
	 /usr/ucblib
	 /usr/ucbinclude
	 /usr/games
	 /usr/local
	 /usr/local/bin
	 /usr/new
	 /usr/old
	 /usr/hosts
	 /usr/include
	 /usr/etc

OPTIONS

       The following options are supported:

       -b    Searches only for binaries.

       -B    Changes or otherwise limits the places where whereis searches for binaries.

       -f    Terminates  the  last  directory list and signals the start of file names, and must be used when any of the -B, -M, or -S options are
	     used.

       -m    Searches only for manual sections.

       -M    Changes or otherwise limits the places where whereis searches for manual sections.

       -s    Searches only for sources.

       -S    Changes or otherwise limit the places where whereis searches for sources.

       -u    Searches for unusual entries. A file is said to be unusual if it does not have one entry of each requested type. Thus `whereis -m	-u
	     *' asks for those files in the current directory which have no documentation.

EXAMPLES

       Example 1 Finding files

       Find all files in /usr/bin which are not documented in /usr/share/man/man1 with source in /usr/src/cmd:

	 example% cd /usr/ucb
	 example% whereis -u -M /usr/share/man/man1 -S /usr/src/cmd -f *

FILES

	   o	  /usr/src/*

	   o	  /usr/{doc,man}/*

	   o	  /etc, /usr/{lib,bin,ucb,old,new,local}

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWscpu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       chdir(2), attributes(5)

BUGS

       Since whereis uses chdir(2) to run faster, pathnames given with the -M, -S, or -B must be full; that is, they must begin with a `/'.

SunOS 5.11							    10 Jan 2000 						       whereis(1B)
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