From Newsgroup: comp.lang.tcl

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" ?
--
"Every time Mitt opens his mouth, a swing state gets its wings."

(Should be on a bumper sticker)
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From Newsgroup: comp.lang.tcl

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" ?

Kenny,
thanks for the question. Here is the answer by a TCL'er without expect knowledge.

"eval" does an additional round of substitutions. This happens for all elements and is intended, if a whole command is included in a variable.

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

Harald


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From Newsgroup: comp.lang.tcl

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.
--
person woman man camera tv
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From Newsgroup: comp.lang.tcl

Kenny McCormack <gazelle@shell.xmission.com> wrote:

ISTM that this {*} thing is a relatively recent addition to the langauge,

Not really, it was added in 8.5, which was released Feb 12, 2016 [1]. Although 2016 *is* relatively recent in regards to many expect scripts.

since Expect has been around for a long time, and most of the scripts that
do this sort of thing were written long ago.

Before 8.5, 'eval' was the way to perform the "splicing" that {*}
provides.


[1] https://www.tcl.tk/software/tcltk/8.5.tml
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From Newsgroup: comp.lang.tcl

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.

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From Newsgroup: comp.lang.tcl

Am 12.09.2024 um 20:45 schrieb Kenny McCormack:

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.

"Relatively recent" is quite relative. Here is the relevant changes file entry:

2006-11-02 (feature change)[TIP 293] Replace {expand} with {*} (hobbs)
*** POTENTIAL INCOMPATIBILITY with previous 8.5 alphas only ***

;-)



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From Newsgroup: comp.lang.tcl

Am 13.09.2024 um 06:32 schrieb Rich:

Kenny McCormack <gazelle@shell.xmission.com> wrote:

ISTM that this {*} thing is a relatively recent addition to the langauge,

Not really, it was added in 8.5, which was released Feb 12, 2016 [1]. Although 2016 *is* relatively recent in regards to many expect scripts.

since Expect has been around for a long time, and most of the scripts that >> do this sort of thing were written long ago.

Before 8.5, 'eval' was the way to perform the "splicing" that {*}
provides.

[1] https://www.tcl.tk/software/tcltk/8.5.tml

Sorry, this date is TCL 8.5.19. The {*} was TCL 8.5.0...
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From Newsgroup: comp.lang.tcl

In article <vc0f9n$ml8n$1@dont-email.me>, Rich <rich@example.invalid> wrote: >Kenny McCormack <gazelle@shell.xmission.com> wrote:

ISTM that this {*} thing is a relatively recent addition to the langauge,

Not really, it was added in 8.5, which was released Feb 12, 2016 [1]. >Although 2016 *is* relatively recent in regards to many expect scripts.

Well, yes, really, from the perspective of Expect.

That was my point - that Expect hasn't really changed much since the late
90s, and most of the active development was done then. The scripts that I
have in mind - such as "unbuffer" - date back to that era.

since Expect has been around for a long time, and most of the scripts that >> do this sort of thing were written long ago.

Before 8.5, 'eval' was the way to perform the "splicing" that {*}
provides.

Right. OK.

I'm glad I learned about {*}.
--
This is the GOP's problem. When you're at the beginning of the year
and you've got nine Democrats running for the nomination, maybe one or
two of them are Dennis Kucinich. When you have nine Republicans, seven
or eight of them are Michelle Bachmann.
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From Newsgroup: comp.lang.tcl

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
--
"Insisting on perfect safety is for people who don't have the balls to live
in the real world."

- Mary Shafer, NASA Ames Dryden -
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From Newsgroup: comp.lang.tcl

In article <vc0lm1$npv9$1@dont-email.me>,
Harald Oehlmann <wortkarg3@yahoo.com> wrote:

Am 12.09.2024 um 20:45 schrieb Kenny McCormack:

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.

"Relatively recent" is quite relative. Here is the relevant changes file >entry:

2006-11-02 (feature change)[TIP 293] Replace {expand} with {*} (hobbs)
*** POTENTIAL INCOMPATIBILITY with previous 8.5 alphas only ***

;-)

The other poster seemed to think 2016 (not 2006). That's still 8 years
ago...
--
Republican Congressman Matt Gaetz claims that only ugly women want
abortions, which they will never need since no one will impregnate them.
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From Newsgroup: comp.lang.tcl

Kenny McCormack <gazelle@shell.xmission.com> wrote:

In article <vc0lm1$npv9$1@dont-email.me>,
Harald Oehlmann <wortkarg3@yahoo.com> wrote:

Am 12.09.2024 um 20:45 schrieb Kenny McCormack:

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.

"Relatively recent" is quite relative. Here is the relevant changes file >>entry:

2006-11-02 (feature change)[TIP 293] Replace {expand} with {*} (hobbs)
*** POTENTIAL INCOMPATIBILITY with previous 8.5 alphas only ***

;-)

The other poster seemed to think 2016 (not 2006). That's still 8 years ago...

I pulled a date for a "point version" of 8.5 instead of 8.5.0.
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