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<TITLE>8.4 String Substitution</TITLE>
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<P><FONT SIZE="5">8.4 String Substitution</FONT><BR>
<P>Most command shells provide some form of string
substitution so as to provide some degree of
parameterization. The FunnelWeb shell provides 36 different
string variables named <SAMP>$0..$9</SAMP> and <SAMP>$A..$Z</SAMP>
(case insensitive). Each variable can hold a string
containing any sequence of printable characters and can be
as long as a command line.
<P>The <SAMP>define</SAMP> command
allows the user to assign a value to these variables. The
<SAMP>define</SAMP> command takes two arguments. The first is
the digit or letter of the variable to be defined. The
second is a double quote delimited string being the string
value to be assigned to the variable. If you want to include
a double quote character within the string, you don't need
to double it.
<P>Examples:
<P>
<PRE>
define 3 "/root/usr/dave/workdir/fwdir/testdir"
define M "/user/local/rubbish/bin/fw"
define Q "You don't need to double" double quotes"
</PRE>
<P>Only the identifying character of the variable being
assigned is used in the definition. This syntax is a simple
way of preventing the variable from being substituted before
it has a chance to be defined!
<P>The following points clean up the remaining semantic
details:
<UL>
<LI> There is only one set of variables and they are
global to all shellscripts. There are <I>no local
variables</I> .
<LI> When a shellscript is invoked using the
<SAMP>execute</SAMP> command, the substitution variables
<SAMP>0</SAMP> through <SAMP>9</SAMP> are affected. See the
EXECUTE command for more details.
<LI> If you want to include a dollar sign character in a
command use "<TT>$$</TT>".
<LI> FunnelWeb also defines "<TT>$/</TT>" which
translates to the character that separates directory and
file name fields in file names on the host machine. For
example: Sun="<TT>/</TT>", Vax="<TT>]</TT>",
Mac="<TT>:</TT>", PC="<TT>\</TT>".
<LI> Substitution is not performed recursively.
</UL>
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