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

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Grouping with Braces and Double Quotes

Double quotes and curly braces are used to group words together into one argument. The difference between double quotes and curly braces is that quotes allow substitutions to occur in the group, while curly braces prevent substitutions. This rule applies to command, variable, and backslash substitutions.

Example 1-10 Grouping with double quotes vs. braces.
set s Hello
=> Hello
puts stdout "The length of $s is [string length $s]."
=> The length of Hello is 5.
puts stdout {The length of $s is [string length $s].}
=> The length of $s is [string length $s].
					

In the second command of Example 1-10, the Tcl interpreter does variable and command substitution on the second argument to puts. In the third command, ...

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