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Top Forums UNIX for Advanced & Expert Users Test -e not working as expected (by me) Post 302937990 by bakunin on Wednesday 11th of March 2015 08:13:21 AM
Old 03-11-2015
Test -e not working as expected (by me)

I ran into the following and still do not understand entirely the rationale behind this. If someone could explain why things are as they are I'd be thankful.

The following was tested on AIX 7.1 with ksh88, but i suspect that to be ubiquitous. In an installation routine i had to create a set of symbolic links. Because they might already exist i used test -e filename to test it:

Code:
if [ ! -e /some/link ] ; then
     ln -s /path/to/file /some/link
fi

This didn't work as expected because test returned 0 only if the link AND its target existed. If only the link exists but not the file referenced by it test will return 1.

The POSIX Documentation about test says:

Code:
-e  pathname
    True if pathname resolves to a file that exists. False if pathname cannot be resolved.

A "file that exists" is IMHO covered by a link, even if this link points to a file which doesn't. I can stat() this file and do many other operations on it which can be done with a file.

I do understand that i can use "-L", which tests for a link but i would like to understand the rationale behind the behavior. Or is the POSIX documentation inconsistent here?

bakunin
 

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LN(1)							    BSD General Commands Manual 						     LN(1)

NAME
ln -- make links SYNOPSIS
ln [-fhinsv] source_file [target_file] ln [-fhinsv] source_file ... target_dir DESCRIPTION
The ln utility creates a new directory entry (linked file) which has the same modes as the original file. It is useful for maintaining mul- tiple copies of a file in many places at once without using up storage for the ``copies''; instead, a link ``points'' to the original copy. There are two types of links: hard links and symbolic links. How a link ``points'' to a file is one of the differences between a hard or symbolic link. The options are as follows: -f Unlink any already existing file, permitting the link to occur. -h If the target_file or target_dir is a symbolic link, do not follow it. This is most useful with the -f option, to replace a symlink which may point to a directory. -i Cause ln to write a prompt to standard error if the target file exists. If the response from the standard input begins with the char- acter 'y' or 'Y', then unlink the target file so that the link may occur. Otherwise, do not attempt the link. (The -i option over- rides any previous -f options.) -n Same as -h, for compatibility with other ln implementations, namely GNU coreutils. -s Create a symbolic link. -v Cause ln to be verbose, showing files as they are processed. By default ln makes hard links. A hard link to a file is indistinguishable from the original directory entry; any changes to a file are effective independent of the name used to reference the file. Hard links may not normally refer to directories and may not span file sys- tems. A symbolic link contains the name of the file to which it is linked. The referenced file is used when an open(2) operation is performed on the link. A stat(2) on a symbolic link will return the linked-to file; an lstat(2) must be done to obtain information about the link. The readlink(2) call may be used to read the contents of a symbolic link. Symbolic links may span file systems and may refer to directories. Given one or two arguments, ln creates a link to an existing file source_file. If target_file is given, the link has that name; target_file may also be a directory in which to place the link; otherwise it is placed in the current directory. If only the directory is specified, the link will be made to the last component of source_file. Given more than two arguments, ln makes links in target_dir to all the named source files. The links made will have the same name as the files being linked to. SEE ALSO
link(2), lstat(2), readlink(2), stat(2), symlink(2), symlink(7) STANDARDS
The ln utility conforms to IEEE Std 1003.2-1992 (``POSIX.2''). The -v option is an extension to IEEE Std 1003.2-1992 (``POSIX.2''). HISTORY
A ln utility appeared in Version 6 AT&T UNIX. BSD
October 29, 2007 BSD
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