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Full Discussion: What is with the '&'.
Top Forums UNIX for Dummies Questions & Answers What is with the '&'. Post 17264 by TioTony on Tuesday 12th of March 2002 10:31:19 PM
Old 03-12-2002
Hello,
The & has several modes of significance on the Unix command line. The 2 most common forms I usually encounter are for running jobs in the background and for redirecting STDERR.

When & appears at the end of a command string, this usually signifies you want that command to run in the background. This returns control of your session back to you. If you submit a command that normally takes 5 minutes with no & on the end of it, you have to wait 5 minutes until the prompt returns. With & on the end, you get the command prompt back immediatly and your commmand continues to run.

The command that follows is actually interpretted by the shell as 2 commands.

rose_pa--root::/data/connect>mkdir &Q2

ksh thinks you are running a command called mkdir and a second command called Q2. mkdir is being put in the background. That is why you get this message:

[1] 29264

This is the process ID of mkdir.

Then the shell tries to run Q2 thinking it is another command. Then you get:

ksh: Q2: not found.

mkdir then completes and gives you the error:

rose_pa--root::/data/connect>Usage: mkdir [-p] [-m mode]
Directory ...


This is because no directory name appeared prior to the &.

I hope this makes sense. You may want to check the man pages for fg as well. This brings background jobs to the foreground.

TioTony
 

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MKDIR(1)						    BSD General Commands Manual 						  MKDIR(1)

NAME
mkdir -- make directories SYNOPSIS
mkdir [-pv] [-m mode] directory_name ... DESCRIPTION
The mkdir utility creates the directories named as operands, in the order specified, using mode ``rwxrwxrwx'' (0777) as modified by the cur- rent umask(2). The options are as follows: -m mode Set the file permission bits of the final created directory to the specified mode. The mode argument can be in any of the formats specified to the chmod(1) command. If a symbolic mode is specified, the operation characters '+' and '-' are interpreted relative to an initial mode of ``a=rwx''. -p Create intermediate directories as required. If this option is not specified, the full path prefix of each operand must already exist. On the other hand, with this option specified, no error will be reported if a directory given as an operand already exists. Intermediate directories are created with permission bits of ``rwxrwxrwx'' (0777) as modified by the current umask, plus write and search permission for the owner. -v Be verbose when creating directories, listing them as they are created. The user must have write permission in the parent directory. EXIT STATUS
The mkdir utility exits 0 on success, and >0 if an error occurs. EXAMPLES
Create a directory named foobar: $ mkdir foobar Create a directory named foobar and set its file mode to 700: $ mkdir -m 700 foobar Create a directory named cow/horse/monkey, creating any non-existent intermediate directories as necessary: $ mkdir -p cow/horse/monkey COMPATIBILITY
The -v option is non-standard and its use in scripts is not recommended. SEE ALSO
rmdir(1) STANDARDS
The mkdir utility is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible. HISTORY
A mkdir command appeared in Version 1 AT&T UNIX. BSD
March 15, 2013 BSD
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