8.4 String Substitution

8.4 String Substitution

Most command shells provide some form of string substitution so as to

provide some degree of parameterization. The FunnelWeb shell provides

Tutorial

36 different string variables named $0..$9 and $A..$Z (case insensitive).

Each variable can hold a string containing any sequence of printable

Developer

characters and can be as long as a command line.

The define command allows the user to assign a value to these variables.

Reference

The define command takes two arguments. The first is the digit or letter of

1 Introduction

the variable to be defined. The second is a double quote delimited string

2 Interface

being the string value to be assigned to the variable. If you want to include

3 Scanner

a double quote character within the string, you don t need to double it.

4 Parser

Examples:

5 Analyser

6 Tangle

define 3 "/root/usr/dave/workdir/fwdir/testdir"

7 Weave

define M "/user/local/rubbish/bin/fw"

8 Shell

define Q "You don t need to double" double quotes"

9 Commands

Only the identifying character of the variable being assigned is used in the

10 Glossary

definition. This syntax is a simple way of preventing the variable from

11 References

being substituted before it has a chance to be defined!

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The following points clean up the remaining semantic details:

There is only one set of variables and they are global to all

G   

shellscripts. There are 

no local variables

 .

When a shellscript is invoked using the execute command, the

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substitution variables 0 through 9 are affected. See the EXECUTE

command for more details.

If you want to include a dollar sign character in a command use

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"

$$

".

FunnelWeb also defines "

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$/

" which translates to the character that

separates directory and file name fields in file names on the host

machine. For example: Sun="

/

", Vax="

]

", Mac="

:

", PC="

\

".

Substitution is not performed recursively.

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Copyright   Ross N. Williams 1992,1999. All rights reserved.

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