You are wary of the Perl environment because it is quite different from the languages you have come across before. The people who believe in strong typing and function prototypes will disagree here, but I believe that restrictions like that are rarely useful. Has C really caught you passing the wrong number of parameters to … Read more
If you had use strict turned on, you would have found out that $++foo doesn’t make any sense. Here’s how to do it: use strict; use warnings; my $file=”SnPmaster.txt”; open my $info, $file or die “Could not open $file: $!”; while( my $line = <$info>) { print $line; last if $. == 2; } close … Read more
There are a few ways: $0 is the currently executing script as provided by POSIX, relative to the current working directory if the script is at or below the CWD Additionally, cwd(), getcwd() and abs_path() are provided by the Cwd module and tell you where the script is being run from The module FindBin provides … Read more
Perl has a syntax called “indirect method notation”. It allows Foo->new($bar) to be written as new Foo $bar So that means Syntax error ! exit 0; is the same as error->Syntax(! exit 0); or error->Syntax(!exit(0)); Not only is it valid syntax, it doesn’t result in a run-time error because the first thing executed is exit(0).
You’ll want to use a coprocess in bash, or in perl with some kind of two-way pipe. In Python you can use the os.popen2 command; perl also has facilities for interacting with subprocesses over pipes. However, it’s much better to use native language database drivers like DBD::Pg or psycopg2 if at all possible. If you … Read more
Perl’s system function has two modes: taking a single string and passing it to the command shell to allow special characters to be processed taking a list of strings, exec’ing the first and passing the remaining strings as arguments In the first form you have to be careful to escape characters that might have a … Read more
There are problems with the design of smart-matching. The decision of what any given TYPE ~~ TYPE should do is most often unobvious, inconsistent and/or disputed. The idea isn’t to remove smart matching; it’s to fix it. Specifically, ~~ will be greatly simplified, as you can see in a proposal by the 5.18 pumpking. Decisions … Read more
Whenever you can use the name of a variable, you can use a block that evaluates to a reference instead. For example, the following are valid syntax for specifying an array: @NAME # If you have the name e.g. @array @BLOCK # If you have a reference e.g. @{ $ref } This is the “circumfix … Read more
Double quotes use variable expansion. Single quotes don’t In a double quoted string you need to escape certain characters to stop them being interpreted differently. In a single quoted string you don’t (except for a backslash if it is the final character in the string) my $var1 = ‘Hello’; my $var2 = “$var1”; my $var3 … Read more
I think you’re misunderstanding what a fork does. When you successfully fork, you’re creating a subprocess, independent from the process you started with, to continue doing work. Because it’s a separate process, it has its own memory, variables, etc., even though some of these started out as copies from the parent process. So you’re setting … Read more