Hi Team,
I need to know why ppl use If true loop instead of just writing down the sequence of code lines.
1:
Code:
echo "Line1"
if true; then
echo "Line2"
fi
echo "Line3"
2:
Code:
echo "Line1"
echo "Line2"
echo "Line3"
Could you explain what does the if true loop make difference in 1st compare to 2nd code?
Regards,
Chandana
I'm not sure what you mean by "if true loop". There is no loop here.
The only time I have seen code like this is during development where true is a placeholder for code to be added later. (But that should never be done without including a comment describing what code needs to be added.)
I have, however, e seen true used as the condition in a while loop to create an obvious infinite loop or a loop where the termination condition occurs in the middle of the loop instead of at the start of the loop or the end of the loop as in:
Code:
echo line1
while true
do echo line2
other stuff
if [ something_failed ]
then break
fi
more stuff
done
echo line3
This User Gave Thanks to Don Cragun For This Post:
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I need help with a script to loop unitl the statement is true
done some thing like this
until
if
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Discussion started by: chandana.hs
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LEARN ABOUT DEBIAN
io::async::test
IO::Async::Test(3pm) User Contributed Perl Documentation IO::Async::Test(3pm)NAME
"IO::Async::Test" - utility functions for use in test scripts
SYNOPSIS
use Test::More tests => 1;
use IO::Async::Test;
use IO::Async::Loop;
my $loop = IO::Async::Loop->new;
testing_loop( $loop );
my $result;
$loop->do_something(
some => args,
on_done => sub {
$result = the_outcome;
}
);
wait_for { defined $result };
is( $result, what_we_expected, 'The event happened' );
...
my $buffer = "";
my $handle = IO::Handle-> ...
wait_for_stream { length $buffer >= 10 } $handle => $buffer;
is( substr( $buffer, 0, 10, "" ), "0123456789", 'Buffer was correct' );
DESCRIPTION
This module provides utility functions that may be useful when writing test scripts for code which uses "IO::Async" (as well as being used
in the "IO::Async" test scripts themselves).
Test scripts are often synchronous by nature; they are a linear sequence of actions to perform, interspersed with assertions which check
for given conditions. This goes against the very nature of "IO::Async" which, being an asynchronisation framework, does not provide a
linear stepped way of working.
In order to write a test, the "wait_for" function provides a way of synchronising the code, so that a given condition is known to hold,
which would typically signify that some event has occured, the outcome of which can now be tested using the usual testing primitives.
Because the primary purpose of "IO::Async" is to provide IO operations on filehandles, a great many tests will likely be based around
connected pipes or socket handles. The "wait_for_stream" function provides a convenient way to wait for some content to be written through
such a connected stream.
FUNCTIONS
testing_loop( $loop )
Set the "IO::Async::Loop" object which the "wait_for" function will loop on.
wait_for( $condfunc )
Repeatedly call the "loop_once" method on the underlying loop (given to the "testing_loop" function), until the given condition function
callback returns true.
To guard against stalled scripts, if the loop indicates a timeout for 10 consequentive seconds, then an error is thrown.
wait_for_stream( $condfunc, $handle, $buffer )
As "wait_for", but will also watch the given IO handle for readability, and whenever it is readable will read bytes in from it into the
given buffer. The buffer is NOT initialised when the function is entered, in case data remains from a previous call.
$buffer can also be a CODE reference, in which case it will be invoked being passed data read from the handle, whenever it is readable.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
perl v5.14.2 2012-10-24 IO::Async::Test(3pm)