few queries on syntax in scripting

[Vishu]

Hi,

I have a script, but i need your help in understanding a small portion of that script.

1) One is, what is this loop doing.. i mean n is assigned value 0, but what does (:) colon doing in while command, if we are specifying range, then it can be specified without colons (:) i think.

typeset -i n=0
 while (( n < ${1:-80} )); do
  (( n+=1 ))
  echo "-\c"
 done

4) Secondly, how we are calculating the value of "u" in below command.

typeset u=$(id)
 u=${u%%\)*}; u=${u#*\(}

Thanks

[Dennis Handly · Accepted solution]

>1) what is this loop doing

Are you asking what the whole fragment is doing or just what the Parameter Substitution is doing?

    ${1:-80}

From the ksh man page:

 ${parameter:-word}  If parameter is set and is non-null, substitute its value; otherwise substitute  word.

If the colon (:) is omitted from the above expressions, the shell only checks to determine whether or not parameter is set.

So the important character is the "-", not the colon.  ;-)

>4) how we are calculating the value of "u"?

typeset u=$(id)
 u=${u%%\)*}; u=${u#*\(}

$ id
uid=###(abc) gid=###(def) groups=...

This removes everything from first ")" to end.  Then removes from the start to the "(".

Note this is all silly because:
$ id -un
###

So just do: typeset u=$(id -un)

>Or, again: man sh

Actually you'll be sorry.  ;-)

You need: man sh-posix

[Vishu]

Thanks Dennis for this clarification...i did read man page, but was bit confused, so turned to you....anyway, thanks again for your help...Your posts always help me out...