How to issue commands from inside a loop?

Question

This is a very basic question.

I think of TCL as a command line generator. Its purpose is to generate strings for the tool’s command line interpreter. For example, the tcl commands:

set alpha “run”
$alpha
$alpha
$alpha

cause the “run” command to be sent to the tool three times – which makes sense. But:

set alpha “run”
for {set i 0} {$i<3} {incr i} $alpha

does not. So the question is: How do I send commands to the tool from inside a loop?

Style point: write the loop as for {set i 0} {$i<3} {incr i} {$alpha} to avoid possible issues with quoting. I hope that's not going to fix it for real for you, but maybe… — Donal Fellows
– Donal Fellows, Commented Apr 25, 2016 at 8:11

Peter Lewerin · Accepted Answer · 2016-04-25 05:58:46Z

1

Your problem is likely to be with the "funny quotes" in the line

set alpha “run”

To Tcl, those quotes aren't syntactic markers, just text. Try

set alpha "run"

or, even better,

set alpha run

answered Apr 25, 2016 at 5:58

Peter Lewerin

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Comments

Sharad · Accepted Answer · 2016-04-25 07:00:40Z

0

Here's a possible way (with output):

% proc foo {count} {
    puts "count = $count"
}
% set alpha foo
foo
% for {set i 0} {$i<3} {incr i} {
    $alpha $i    
}
count = 0
count = 1
count = 2
%

edited Apr 25, 2016 at 7:00

answered Apr 25, 2016 at 3:38

Sharad

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2 Comments

Peter Lewerin Over a year ago

The use of eval is unnecessary here and can actually break things if any of the arguments has list structure.

Sharad Over a year ago

@PeterLewerin Agree. Thanks. Updated the snippet above.

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