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Full Discussion: ":" operator???
Top Forums Shell Programming and Scripting ":" operator??? Post 302408361 by TonyLawrence on Monday 29th of March 2010 11:06:56 AM
Old 03-29-2010
Quote:
Originally Posted by jlliagre
It is the "null" shell builtin. It does nothing but unlike a comment "#", it processes redirections and expands parameters.
True, but the question is why would you do such a thing?

The answer is usually portability. If your script needs to ">file", that alone won't work everywhere and neither will "echo -n > file" or "echo "\c". That ": >file" will work.

---------- Post updated at 11:06 AM ---------- Previous update was at 09:30 AM ----------

Oh, and the other thing:

: ${nomeutente=‘whoami‘}

is because a bare

${nomeutente=‘whoami‘}

would try to execute the result. So if "whoami" is "ls", then "ls" would run. If it's "azrtyuw" it would also try to run and you'd get an error.

In this particular case you could just do

n=`whoami`

but consider

: ${nomeutente:=‘whoami‘}

(sets nomeutente only if not already set)

You'd need if-then or a case block otherwise which is much longer and possibly confusing.
 

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LEARN ABOUT OPENSOLARIS

whoami

whoami(1B)					     SunOS/BSD Compatibility Package Commands						whoami(1B)

NAME

       whoami - display the effective current username

SYNOPSIS

       /usr/ucb/whoami

DESCRIPTION

       whoami  displays  the  login  name  corresponding  to the current effective user ID. If you have used su to temporarily adopt another user,
       whoami will report the login name associated with that user ID. whoami gets its information from the geteuid and getpwuid library  routines
       (see getuid and getpwnam(3C), respectively).

FILES

       /etc/passwd    username data base

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWscpu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       su(1M), who(1), getuid(2), getpwnam(3C), attributes(5)

SunOS 5.11							    14 Sep 1992 							whoami(1B)
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