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Full Discussion: Mkdir
Top Forums UNIX for Beginners Questions & Answers Mkdir Post 302992012 by drysdalk on Monday 20th of February 2017 02:41:29 PM
Old 02-20-2017
Hi,

Taking them in turn:

mkdir test and mkdir ./test

In practical terms, there isn't likely to be much difference between them, and they are generally going to be interchangebale in use. The key to understanding what they do though (and why they both do the same thing) is understanding the meaning of './' specifically.

In UNIX-style nomenclature, the '.' character represents your current directory. The '/' symbol is the path separator, and is used to separate one directory in a path from another. All absolute paths starting at the root of the filesystem tree begin with '/'.

So, in the first instance, mkdir test simpy creates a directory called 'test' in your current working directory, without specifying a path. In effect, this works out to be identical to specificying the current working directory in your path by doing mkdir ./test.

In both cases, you're going to end up with a sub-directory of your current working directory (that is, the directory you are in when you run the 'mkdir' command) called 'test'. Most commands (mkdir amongst them) are generally going to assume if you don't specify a path you must be referring to your current directory, which is why in this one single instance you can use both these forms interchangeably.

Moving on to your second question:

if ( -e /test ) then and if ( -e ./test ) then

Here there's a big difference in meaning, and these two tests will do entirely different things. The path '/test' refers to a file or directory beneath the root of the filesystem (that is, the very top of the filesystem tree) called 'test'. Whereas './test' refers to a file or directory beneath your current working directory called 'test'.

So unless you happen to have / as your current working directory, the meaning of these will be very different. '/test' will always refer to something called 'test' underneath the root directory, no matter where you happen to be yourself in the file system tree at the time. Whereas './test' will always refer to something called 'test' underneath whatever directory you happen to be in at the time.

Hope this helps.
 

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LEARN ABOUT HPUX

fchdir

chdir(2)							System Calls Manual							  chdir(2)

NAME

       chdir, fchdir - change working directory

SYNOPSIS

DESCRIPTION

       and  cause  a  directory pointed to by path or fildes to become the current working directory, the starting point for path searches of path
       names not beginning with path points to the path name of a directory.  fildes is an open file descriptor of a directory.

       For a directory to become the current working directory, a process must have execute (search) access to the directory.

RETURN VALUE

       Upon successful completion, a value of 0 is returned.  Otherwise, a value of -1 is returned and is set to indicate the error.

ERRORS

       fails and the current working directory remains unchanged if one or more of the following are true:

	      A component of the path name is not a directory.

	      The named directory does not exist.

	      Search permission is denied for any component of the path name.

	      path		    points outside the allocated address space of the process.	The reliable detection of this error is  implemen-
				    tation dependent.

	      path		    is null.

	      The length of the specified path name exceeds
				    bytes, or the length of a component of the path name exceeds bytes while is in effect.

	      Too many symbolic links were encountered in translating the path name.

       fails and the current working directory remains unchanged if one or more of the following are true:

	      Search permission is denied for
				    fildes.

	      fildes		    is not an open file descriptor.

	      The open file descriptor
				    fildes does not refer to a directory.

AUTHOR

       and were developed by AT&T Bell Laboratories and HP.

SEE ALSO

       cd(1), chroot(2), privileges(5).

STANDARDS CONFORMANCE

																	  chdir(2)
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