What's the purpose of the following two lines of perl??
my $host = shift || 'localhost';
my $port = shift || 200;
That should return localhost and port 10. What is the shift keyword??
What this piece of code is, is a way to provide default values for $host
and $port
. It will typically be at the start of a script or a subroutine, and take values from @ARGV
and @_
respectively.
That should return localhost and port 10.
No, the ||
operator is a short circuiting OR
, which means that if the LHS operand returns a true value, the RHS operand is ignored. Basically, it means this (and ONLY this): "choose the left hand side value if it is true, otherwise choose the right hand side value."
shift ARRAY
will return the first value of ARRAY
, or:
If ARRAY is omitted, shifts the @_ array within the lexical scope of subroutines and formats, and the @ARGV array outside a subroutine and also within the lexical scopes established by the eval STRING , BEGIN {} , INIT {} , CHECK {} , UNITCHECK {} and END {} constructs.
Quoted from http://perldoc.perl.org/functions/shift.html
Also, of course, shift
removes the value from the array that is shifted. Therefore you can have two shift
in a row like this, for very convenient argument handling.