日志
tcl
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- In Tcl, the evaluation of a command is done is 2 phases. The first phase is a single pass of substitutions. The second phase is the evaluation of the resulting command. Note that only one pass of substitutions is made.
- A command within square brackets ([]) is replaced with the return from the execution of that command.
- Grouping words within double quotes allows substitutions to occur within the quotations. The substituted group is then evaluated as a single argument.
- The
exprcommand performs its own round of substitutions on variables and commands, so you should use braces to prevent the Tcl interpreter doing this as well (leading to double substitution) - Many commands use
exprbehind the scenes in order to evaluate test expressions, such asif,whileandforloops, discussed in later sections.
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