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From: Rich <rich@example.invalid>
Newsgroups: comp.lang.tcl
Subject: Re: Why do we need "eval"? (Expect question)
Date: Fri, 13 Sep 2024 04:36:04 -0000 (UTC)
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Harald Oehlmann <wortkarg3@yahoo.com> wrote:
> spawn -noecho printf {\t%s\n} {*}$argv
> eventually, this works to:
> spawn -noecho printf \t%s\n {*}$argv

Do note that the second one causes \t and \n to be interpreted by Tcl's 
parser, so printf gets passed a literal tab and literal newline in its 
parameter list.  The first passes the \ and t characters on to printf, 
and then printf does the interpretation.

Both likely work fine for printf, but may not work fine for all 
possible external commands.