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

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Substitution and Grouping Summary

The following rules summarize the fundamental mechanisms of grouping and substitution that are performed by the Tcl interpreter before it invokes a command:

  • Command arguments are separated by white space, unless arguments are grouped with curly braces or double quotes as described below.

  • Grouping with curly braces, { }, prevents substitutions. Braces nest. The interpreter includes all characters between the matching left and right brace in the group, including newlines, semicolons, and nested braces. The enclosing (i.e., outermost) braces are not included in the group's value.

  • Grouping with double quotes, “ ”, allows substitutions. The interpreter groups everything until another double quote is found, including ...

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