Shebang

Introduction#

Shebang is a special symbol in Unix and Unix-like operating systems, composed of the characters #!, used to indicate which interpreter should execute a script file. It usually appears at the beginning of a script file, followed by the path of the interpreter. Shebang allows script files to be run directly like executable programs, without manually calling the interpreter.

Origin of the Name#

# in English represents hash or sharp, ! in programming and command lines represents bang, and the combination of these two symbols is called hash-bang or sharp-bang. Over time, hash-bang was simplified to shebang.

Specifying the Interpreter#

The path specified after Shebang is the location of the interpreter, such as:

#!/bin/bash

The system will use the bash under this path to execute the script content.

Unified Execution Form#

Scripts of different types can be uniformly executed using the form ./file, without explicitly calling the interpreter.

#!/bin/bash

No need to use bash file to execute, directly use ./file.

#!/bin/python3

No need to use python file to execute, directly use ./file.

Common Examples#

We often see the following examples in bash scripts.

#!/usr/bin/env bash

env is a command related to environment variables. When the argument following it is bash, it will search for the bash interpreter based on the path provided by the environment variable PATH. The advantage of doing this is that there is no need to hard-code the path of the bash interpreter, because the bash interpreter may be in different locations in different systems.

type -a bash

bash is /usr/bin/bash
bash is /bin/bash

For the above python example, a better Shebang is to use env.

#!/usr/bin/env python

Manual Invocation#

If there is no Shebang, the interpreter can be manually called.

bash script.sh