shebanglinje

A shebang line, or shebanglinje in many Scandinavian languages, is the first line of a script that starts with the characters #! followed by the path to an interpreter. On Unix-like systems, the kernel uses this line to determine which program should execute the script, allowing the script to be run directly as an executable without explicitly invoking the interpreter.

How it works: when a script with a valid shebang is executed as a program, the operating system launches the specified interpreter and passes the script file as an argument. This enables scripts written in different languages (such as sh, Python, Perl, or Ruby) to be run with a single, portable command. A common convention is to use an explicit path like /bin/sh or /usr/bin/python, or to use /usr/bin/env to locate the interpreter in the user’s PATH, for example #!/usr/bin/env python3, which improves portability across systems where interpreter locations vary.

Execution requirements and portability: to run as a command, the script file must have executable permission (for example, chmod +x on Unix-like systems). The behavior of shebang lines is specific to Unix-like environments; Windows does not use shebangs to determine executability, though some environments (such as Git Bash, Cygwin, or the Windows Subsystem for Linux) emulate similar behavior.

Common examples:

- #!/usr/bin/env python3

- #!/bin/sh

Overall, the shebang line provides a simple, portable way to specify the interpreter for a script, enabling cross-language scripting with minimal boilerplate.