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Top Forums Shell Programming and Scripting 'Dynamic' setting of variables in bash script Post 302893301 by Subbeh on Tuesday 18th of March 2014 11:49:57 AM
Old 03-18-2014
Quote:
Originally Posted by Corona688
This is a poor example because, if someone tried to name an array `rm -Rf ~/`, eval would happily execute that and erase your home directory.

We get dozens and dozens of requests for dynamic variable names, but they don't generally make much sense. How would you even use those variables afterwards? If you take a good look at what you're trying to do, there's usually ways to do it in a far more straightforward way.

One way is arrays. Another way is just not storing the data at all -- you don't have to keep absolutely everything stored in memory at all times. If you only intend to use the lines one at a time, there's no point -- just use them as you read them, then throw them away.
I agree with the use of eval, but I'm confused with your response to my example where I'm suggesting arrays instead of eval. In what way is this a poor example?
 

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variable(n)						       Tcl Built-In Commands						       variable(n)

__________________________________________________________________________________________________________________________________________________

NAME
variable - create and initialize a namespace variable SYNOPSIS
variable ?name value...? name ?value? _________________________________________________________________ DESCRIPTION
This command is normally used within a namespace eval command to create one or more variables within a namespace. Each variable name is initialized with value. The value for the last variable is optional. If a variable name does not exist, it is created. In this case, if value is specified, it is assigned to the newly created variable. If no value is specified, the new variable is left undefined. If the variable already exists, it is set to value if value is specified or left unchanged if no value is given. Normally, name is unqualified (does not include the names of any containing namespaces), and the variable is created in the current namespace. If name includes any namespace qualifiers, the variable is created in the specified names- pace. If the variable is not defined, it will be visible to the namespace which command, but not to the info exists command. If the variable command is executed inside a Tcl procedure, it creates local variables linked to the corresponding namespace variables (and therefore these variables are listed by info vars.) In this way the variable command resembles the global command, although the global command only links to variables in the global namespace. If any values are given, they are used to modify the values of the associated namespace variables. If a namespace variable does not exist, it is created and optionally initialized. A name argument cannot reference an element within an array. Instead, name should reference the entire array, and the initialization value should be left off. After the variable has been declared, elements within the array can be set using ordinary set or array commands. EXAMPLES
Create a variable in a namespace: namespace eval foo { variable bar 12345 } Create an array in a namespace: namespace eval someNS { variable someAry array set someAry { someName someValue otherName otherValue } } Access variables in namespaces from a procedure: namespace eval foo { proc spong {} { # Variable in this namespace variable bar puts "bar is $bar" # Variable in another namespace variable ::someNS::someAry parray someAry } } SEE ALSO
global(n), namespace(n), upvar(n) KEYWORDS
global, namespace, procedure, variable Tcl 8.0 variable(n)
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