"while :" would mean to do a loop of the whole while - do block. On this case, it is supposed to echo the question until the user either answers a Y (which on this case will execute the break command) and a N (which will exit the script).
If you put the inner while-do block outside of the outer while-do, the routine will work. It is only when it is inside the outer while-do that the routine goes into loop.
Quote:
Originally Posted by porter
1. what does "while :" mean?
2. everything inside the while/read/do/done will use testdata as stdin, including the "read YESNO", you would need to do
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Discussion started by: yifangt
3 Replies
LEARN ABOUT OPENDARWIN
while
while(n) Tcl Built-In Commands while(n)
__________________________________________________________________________________________________________________________________________________NAME
while - Execute script repeatedly as long as a condition is met
SYNOPSIS
while test body
_________________________________________________________________DESCRIPTION
The while command evaluates test as an expression (in the same way that expr evaluates its argument). The value of the expression must a
proper boolean value; if it is a true value then body is executed by passing it to the Tcl interpreter. Once body has been executed then
test is evaluated again, and the process repeats until eventually test evaluates to a false boolean value. Continue commands may be exe-
cuted inside body to terminate the current iteration of the loop, and break commands may be executed inside body to cause immediate termi-
nation of the while command. The while command always returns an empty string.
Note: test should almost always be enclosed in braces. If not, variable substitutions will be made before the while command starts execut-
ing, which means that variable changes made by the loop body will not be considered in the expression. This is likely to result in an
infinite loop. If test is enclosed in braces, variable substitutions are delayed until the expression is evaluated (before each loop iter-
ation), so changes in the variables will be visible. For an example, try the following script with and without the braces around $x<10:
set x 0
while {$x<10} {
puts "x is $x"
incr x
}
SEE ALSO
break(n), continue(n), for(n), foreach(n)
KEYWORDS
boolean value, loop, test, while
Tcl while(n)