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><H1
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><A
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>Variable variables</A
></H1
><P
>&#13;    Sometimes it is convenient to be able to have variable variable
    names.  That is, a variable name which can be set and used
    dynamically.  A normal variable is set with a statement such as:
   </P
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>&#13;$a = "hello";
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>&#13;    A variable variable takes the value of a variable and treats that
    as the name of a variable.  In the above example,
    <I
CLASS="emphasis"
>hello</I
>, can be used as the name of a variable
    by using two dollar signs. i.e.
   </P
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>&#13;$$a = "world";
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>&#13;    At this point two variables have been defined and stored in the
    PHP symbol tree: <TT
CLASS="varname"
>$a</TT
> with contents "hello" and
    <TT
CLASS="varname"
>$hello</TT
> with contents "world".  Therefore, this
    statement:
   </P
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>&#13;echo "$a ${$a}";
    </PRE
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>&#13;    produces the exact same output as:
   </P
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>&#13;echo "$a $hello";
    </PRE
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><P
>&#13;    i.e. they both produce: <TT
CLASS="computeroutput"
>hello world</TT
>.
   </P
><P
>&#13;    In order to use variable variables with arrays, you have to
    resolve an ambiguity problem.  That is, if you write
    <TT
CLASS="varname"
>$$a[1]</TT
> then the parser needs to know if you
    meant to use <TT
CLASS="varname"
>$a[1]</TT
> as a variable, or if you
    wanted <TT
CLASS="varname"
>$$a</TT
> as the variable and then the [1]
    index from that variable.  The syntax for resolving this ambiguity
    is: <TT
CLASS="varname"
>${$a[1]}</TT
> for the first case and
    <TT
CLASS="varname"
>${$a}[1]</TT
> for the second.
   </P
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