Assigning using ternary operator?
I’d usually write this as: $review = ( defined($model->test) ? 1 : ” ); where the parentheses are for clarity for other people reading the code.
perl
Why are use warnings; use strict; not default in Perl?
It’s for backwards compatibility. Perl 4 didn’t have strict at all, and there are most likely still scripts out there originally written for Perl 4 that still work fine with Perl 5. Making strict automatic would break those scripts. The situation is even worse for one-liners, many of which don’t bother to declare variables. Making … Read more
How can I store the result of a system command in a Perl variable?
From Perlfaq8: You’re confusing the purpose of system() and backticks (“). system() runs a command and returns exit status information (as a 16 bit value: the low 7 bits are the signal the process died from, if any, and the high 8 bits are the actual exit value). Backticks (“) run a command and return … Read more
Forcing a list context in Perl
You’re confused because you think = is a single operator while it can result in two different operators: a list assignment operator or a scalar assignment operator. Mini-Tutorial: Scalar vs List Assignment Operator explains the differences. my $b = (33,22,11); —————— Scalar assign in void context. ———- List literal in scalar context. Returns last. my … Read more
Why is Perl so afraid of “deep recursion”?
Because in Haskell, we have laziness & guarded recursion and tail call optimization and Perl has neither. This essentially means that every function call allocates a set amount of memory called “the stack” until the function returns. When you write recursive code, you build up a huge amount of memory because of these nested function … Read more
export vs export_ok in perl
Let’s say I have a package MyPackage that uses @EXPORT. #this is MyPackage.pm package MyPackage; @EXPORT = qw(do_awesome_thing); sub do_awesome_thing { … } sub be_awesome { … } Now, when I use MyPackage in my code, #this is myscript.pl use MyPackage; do_awesome_thing(); #works be_awesome(); #doesn’t work MyPackage::be_awesome(); #works do_awesome_thing gets automatically exported to my code … Read more
Passing a Function Object and Calling it
Here’s a complete, working script that demonstrates what you’re asking. sub a { print “Hello World!\n”; } sub b { my $func = $_[0]; $func->(); } b(\&a); Here’s an explanation: you take a reference to function a by saying \&a. At that point you have a function reference; while normally a function would be called … Read more
How to run CGI scripts on Nginx
Nginx doesn’t have native CGI support (it supports fastCGI instead). The typical solution for this is to run your Perl script as a fastCGI process and edit the nginx config file to re-direct requests to the fastCGI process. This is quite a complex solution if all you want to do is run a CGI script. … Read more
How do I download a file using Perl?
I’d use LWP::Simple for this. #!/usr/bin/perl use strict; use warnings; use LWP::Simple; my $url=”http://marinetraffic2.aegean.gr/ais/getkml.aspx”; my $file=”data.kml”; getstore($url, $file);
How to produce range with step in Perl
perldoc -f map is one way: use warnings; use strict; use Data::Dumper; my @ns = map { 5 * $_ } 1 .. 4; print Dumper(\@ns); __END__ $VAR1 = [ 5, 10, 15, 20 ]; See also: perldoc perlop