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Practical Programming in Tcl & Tk, Third Edition by Brent B. Welch

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Transforming Data to Program with regsub

One of the most powerful combinations of Tcl commands is regsub and subst. This section describes a few examples that use regsub to transform data into Tcl commands, and then use subst to replace those commands with a new version of the data. This technique is very efficient because it relies on two subsystems that are written in highly optimized C code: the regular expression engine and the Tcl parser. These examples are primarily written by Stephen Uhler.

URL Decoding

When a URL is transmitted over the network, it is encoded by replacing special characters with a %xx sequence, where xx is the hexadecimal code for the character. In addition, spaces are replaced with a plus (+). It would be tedious and ...

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