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Copyright (c) Ross N. Williams 1992,1999. All rights reserved.
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<TITLE>8.4 String Substitution</TITLE>
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<P><FONT SIZE="5">8.4 String Substitution</FONT><BR>
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<P>Most command shells provide some form of string
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substitution so as to provide some degree of
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parameterization. The FunnelWeb shell provides 36 different
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string variables named <SAMP>$0..$9</SAMP> and <SAMP>$A..$Z</SAMP>
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(case insensitive). Each variable can hold a string
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containing any sequence of printable characters and can be
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as long as a command line.
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<P>The <SAMP>define</SAMP> command
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allows the user to assign a value to these variables. The
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<SAMP>define</SAMP> command takes two arguments. The first is
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the digit or letter of the variable to be defined. The
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second is a double quote delimited string being the string
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value to be assigned to the variable. If you want to include
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a double quote character within the string, you don't need
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define 3 "/root/usr/dave/workdir/fwdir/testdir"
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define M "/user/local/rubbish/bin/fw"
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define Q "You don't need to double" double quotes"
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<P>Only the identifying character of the variable being
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assigned is used in the definition. This syntax is a simple
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way of preventing the variable from being substituted before
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it has a chance to be defined!
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<P>The following points clean up the remaining semantic
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<LI> There is only one set of variables and they are
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global to all shellscripts. There are <I>no local
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<LI> When a shellscript is invoked using the
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<SAMP>execute</SAMP> command, the substitution variables
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<SAMP>0</SAMP> through <SAMP>9</SAMP> are affected. See the
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EXECUTE command for more details.
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<LI> If you want to include a dollar sign character in a
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command use "<TT>$$</TT>".
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<LI> FunnelWeb also defines "<TT>$/</TT>" which
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translates to the character that separates directory and
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file name fields in file names on the host machine. For
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example: Sun="<TT>/</TT>", Vax="<TT>]</TT>",
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Mac="<TT>:</TT>", PC="<TT>\</TT>".
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<LI> Substitution is not performed recursively.
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