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#!/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 ...
In this example, /usr/bin/env is the full path of the env command. The environment is not altered. Note that it is possible to specify the interpreter without using env, by giving the full path of the python interpreter. A problem with that approach is that on different computer systems, the exact path may be different.
If a script is invoked as an argument to the interpreting shell, it will be executed regardless of whether the user holds the execute permission for that script. Although Windows also specifies an execute permission, none of the Windows-specific shells block script execution if the permission has not been granted.
The restricted shell is a Unix shell that restricts some of the capabilities available to an interactive user session, or to a shell script, running within it.It is intended to provide an additional layer of security, but is insufficient to allow execution of entirely untrusted software.
A running program can access the values of environment variables for configuration purposes. Shell scripts and batch files use environment variables to communicate data and preferences to child processes. They can also be used to store temporary values for reference later in a shell script.
tcsh and sh shell windows on a Mac OS X Leopard [1] desktop. A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using ...
The file owner is 'root' and the SUID permission is set (the '4') - so the file is executed as 'root'. The reason an executable would be run as 'root' is so that it can modify specific files that the user would not normally be allowed to, without giving the user full root access. A default use of this can be seen with the /usr/bin/passwd binary ...
The subscript of ENVIRON is the name of an environment variable; its result is the variable's value. This is like the getenv function in various standard libraries and POSIX. The shell script makes an environment variable pattern containing the first argument, then drops that argument and has awk look for the pattern in each file.