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Full Discussion: Indirect variables in Bash
Top Forums Shell Programming and Scripting Indirect variables in Bash Post 302782309 by Scrutinizer on Monday 18th of March 2013 01:53:17 PM
Old 03-18-2013
Quote:
Originally Posted by Corona688
[..]

Code:
A="abc"
B="def"

read $A$B <<<"string"

...should put the string "string" into the variable named abcdef.

This is how it's often used:
Code:
read VARNAME

...but note that it takes a variable name -- a string -- not the variable itself. You can feed it whatever string you please, derived from whatever variables you please, and do things that would otherwise require ugly insecure eval hacks.
[..]
But this method would also have its security risks, but on the left hand side, no? One must control the contents of variables A and B...
*edit* To elaborate: I came across this page

Quote:
with bash, you must still be careful about what is on the left-hand side of the assignment. Inside square brackets, expansions are still performed; thus, with a tainted ref, declare can be just as dangerous as eval:
Code:
# Bash:
 ref='x[$(touch evilfile; echo 0)]'
 ls -l evilfile   # No such file or directory
 declare "$ref=value"
 ls -l evilfile   # It exists now!

The same applies to the read $var construct. I tried this also in ksh93 and then there is an error message ( arithmetic syntax error ) and the code does not get executed..

Last edited by Scrutinizer; 03-18-2013 at 05:21 PM..
 

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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 locals.) 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. SEE ALSO
global(n), namespace(n), upvar(n) KEYWORDS
global, namespace, procedure, variable Tcl 8.0 variable(n)
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