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In most of today's popular programming languages and operating systems, a computer program usually only has a single entry point.. In C, C++, D, Zig, Rust and Kotlin programs this is a function named main; in Java it is a static method named main (although the class must be specified at the invocation time), and in C# it is a static method named Main.
#!/usr/bin/perl – called the "shebang line", after the hash symbol (#) and ! (bang) at the beginning of the line. It is also known as the interpreter directive. # – the number sign, also called the hash symbol. In Perl, the # indicates the start of a comment. It instructs perl to ignore the rest of the line and not execute it as script code.
The hash mark character introduces a comment in Perl, which runs up to the end of the line of code and is ignored by the compiler (except on Windows). The comment used here is of a special kind: it’s called the shebang line.
Raku (previously called Perl 6) uses the same line comments and POD comments as Perl, but adds a configurable block comment type: "multi-line / embedded comments". [42] It starts with #` and then an opening bracket character and ends with the matching closing bracket character. [42] For example:
Perl 5.6.1 and newer support autovivification of file and directory handles. [3] Calling open() on an undefined variable will set it to a filehandle. According to perl561delta, "[t]his largely eliminates the need for typeglobs when opening filehandles that must be passed around, as in the following example:
#! /usr/bin/env python3 – Execute with a Python interpreter, using the env program search path to find it #! /bin/false – Do nothing, but return a non-zero exit status , indicating failure. Used to prevent stand-alone execution of a script file intended for execution in a specific context, such as by the . command from sh/bash, source from ...
Diagram of the mechanism of using perl modules. A Perl module is a discrete component of software for the Perl programming language.Technically, it is a particular set of conventions for using Perl's package mechanism that has become universally adopted.
Perl. Block comments in Perl are considered part of the documentation, and are given the name Plain Old Documentation (POD). Technically, Perl does not have a convention for including block comments in source code, but POD is routinely used as a workaround. PHP. PHP supports standard C/C++ style comments, but supports Perl style as well. Python