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use of hyphen in #! line

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# 1  
Old 03-28-2007
use of hyphen in #! line
In one script i have seen - in #! line can somebody explain the meaning of -(hyphen) here

Code:
#! /bin/sh -

# 2  
Old 03-28-2007
I don't think it serves any useful purpose.
# 3  
Old 03-28-2007
At first view and some experimenting i think you are right but i would request somebody who knows the answer pls explain.
# 4  
Old 03-28-2007
ok, my explanation...

well, looking through man sh there is no hyphen command line.
as we all know Smilie if $0 begins with a '-' then it is a login script,
but this is not the case. Often a lone - (e.g cat - )
means take stdin, well a #! line takes stdin as the file anyway
so I think myself it's a redundant use of this meaning.


p.s. I have no work today
# 5  
Old 03-28-2007
Code:
echo 'ls' | sh -

does exactly what you expect, sh reads from stdin. I think it's an artifact from very antique systems. Chris F A Johnson posts here and will know definitely.
# 6  
Old 03-28-2007
See this page and scroll down to the RATIONALE section near the end.
# 7  
Old 03-29-2007
Thank you all for the interest.What i found is this is something related with the security and prevent some kind of spoofing attacks(mainly with sid).
The text posted below is from the link posted by Perderabo.
Quote:
sh -
or by:
#! usr/bin/sh -
the historical systems have assumed that no option letters follow. Thus, this volume of IEEE Std 1003.1-2001 allows the single hyphen to mark the end of the options, in addition to the use of the regular "--" argument, because it was considered that the older practice was so pervasive. An alternative approach is taken by the KornShell, where real and effective user/group IDs must match for an interactive shell; this behavior is specifically allowed by this volume of IEEE Std 1003.1-2001.

Note:
There are other problems with set-user-ID scripts that the two approaches described here do not resolve.
But still i am not able to understand what is it.I would appreciate if somebody can explain it in simple language.
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