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From: gazelle@shell.xmission.com (Kenny McCormack)
Newsgroups: comp.lang.tcl
Subject: Re: Why do we need "eval"? (Expect question)
Date: Fri, 13 Sep 2024 11:26:10 -0000 (UTC)
Organization: The official candy of the new Millennium
Message-ID: <vc17gi$1u8fb$2@news.xmission.com>
References: <vbv03t$1t4qm$1@news.xmission.com> <vbv8kd$blsb$1@dont-email.me> <vc0ffk$ml8n$2@dont-email.me>
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In article <vc0ffk$ml8n$2@dont-email.me>, Rich  <rich@example.invalid> wrote:
>Harald Oehlmann <wortkarg3@yahoo.com> wrote:
>> spawn -noecho printf {\t%s\n} {*}$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.
>

I think you misunderstand Harald's post (i.e., his notation).

The point is that if you pass {{\t%s\n}} to "eval", both sets of braces get
removed and what "printf" sees is (literally)

    backslash tee percent ess backslash en

If you only pass a single level of braces, and eval it, then yes, as you
said, printf will see

    tab percent ess newline

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