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Old 02-09-2014, 10:26 PM   #1
phillyfilly
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The difference a minus sign makes


What is the difference between these two lines? What does the minus sign at the end do, or don't do? I am running Fedora 20 -64 bit - on VMware Workstation 10. Thank you very much.

df -h
df -h -

php -v
php -v - what does v mean?

rpm -qa
rpm -qa - what does -q-a mean?

mySQL -v
mySQL -v - same question

mySQL -V
mySQL -V - same question

Last edited by phillyfilly; 02-09-2014 at 10:27 PM.
 
Old 02-09-2014, 10:39 PM   #2
m.a.l.'s pa
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Code:
$ df -h -
df: -: No such file or directory
 
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Old 02-09-2014, 10:42 PM   #3
astrogeek
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It has no general or special meaning, it is just another shell argument.

What it does depends on the program or command being invoked.

Some, such as su define the trailing dash to have a particular meaning.

Others do not, and simply ignore it, such as your php and mysql examples.

If you type the df -h - example you will see that it is rejected as an invalid path spec.
 
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Old 02-09-2014, 10:50 PM   #4
m.a.l.'s pa
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Quote:
Originally Posted by phillyfilly View Post
php -v
php -v - what does v mean?
As copied right from man php:

Code:
-v

Version number
 
Old 02-09-2014, 11:38 PM   #5
phillyfilly
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Thank you. There are lots of v's. I thought it meant verbose, but that made no sense.

Last edited by phillyfilly; 02-09-2014 at 11:39 PM.
 
Old 02-10-2014, 02:44 AM   #6
chrism01
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It varies for every cmd; just read the man page, either on your system 'man <cmd>' or here http://linux.die.net/man/
 
Old 02-10-2014, 03:33 AM   #7
pan64
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there are some common flags, like -v means -verbose or -version, -l means long format, -h help, but you always need to check the manual page, because they may have different meaning.
The - (minus) sign usually means the actual process will use stdin as input instead of a file. Is accepted only where it has any meaning (df need no input file).
see for example man grep:
Quote:
Description

grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus (-) is given as file name) for lines containing a match to the given PATTERN. ...
 
Old 02-10-2014, 06:35 AM   #8
yooden
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Quote:
Originally Posted by pan64 View Post
The - (minus) sign usually means the actual process will use stdin as input instead of a file. Is accepted only where it has any meaning (df need no input file).
Not really, see bash(1), su(1).

Your first advice fits: Check the manpage.
 
  


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