What should the first line of a bash shell script typically contain?

The first line of a bash shell script is commonly known as the "shebang" line, and it indicates which interpreter should be used to execute the script. The correct answer, which specifies #!/bin/bash, directly points to the bash shell located in the /bin directory. This is a standard location for the bash interpreter on many Unix-like systems.

Using this shebang ensures that when the script is run, it utilizes the bash shell specifically, which is important because different shells may have different syntax and features. This line instructs the operating system to look for the bash executable in the specified path to interpret the script's commands.

The other option that also indicates the use of bash, #!/usr/bin/env bash, is valid and widely used as it makes the script more portable across different systems where bash may not be located in the same directory. However, #!/bin/bash is a direct reference to the bash executable.

Options that reference invalid or non-standard paths or include erroneous formatting do not correctly fulfill the purpose of directing the script to use the appropriate interpreter. Thus, the choice identifying /bin/bash is seen as the most specific and common designation for a bash shell script's shebang line.