Re: Why do we need "eval"? (Expect question)

In article <vbv8kd$blsb$1@dont-email.me>,
Harald Oehlmann  <wortkarg3@yahoo.com> wrote:

Am 12.09.2024 um 17:07 schrieb Kenny McCormack:

Consider this (Unix/Linux/bash) command line:
 
$ expect -- /dev/fd/3 3<<< 'eval spawn -noecho printf {{\t%s\n}}

$argv;interact' $(seq 1 10)

 
This correctly generates the output (each line starts with a tab):
 
1
2
3
4
5
6
7
8
9
10
 
But notice how we have to use "eval" in order to split up the args in $argv.
And, since we are using "eval", we have to "double quote" (with {}) the
"format" arg to "printf".  It'd be nice if neither of these things were
necessary.
 
I've always believed that "eval" was "evil" and to be avoided if at all
possible - both in shell and in Tcl.  It has strange side effects, such as
we see here (the need to "double quote").  Is there any way to get the
above effect w/o using "eval" ?
 

...

To only expand some arguments, the list expansion operator may be used:
>
In your case:
eval spawn -noecho printf {{\t%s\n}} $argv
equal to:
spawn -noecho printf {\t%s\n} {*}$argv
eventually, this works to:
spawn -noecho printf \t%s\n {*}$argv

Indeed it does.  Thanks!  This solves my issue.

ISTM that this {*} thing is a relatively recent addition to the langauge,
since Expect has been around for a long time, and most of the scripts that
do this sort of thing were written long ago.

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