In a Unix shell script, the interpreter directive on the first line begins…

Concept

When an executable text file is launched directly, Unix can use an interpreter directive, commonly called a shebang, at the very start of the file. Its two-character marker is #!, followed by the path of the interpreter, such as /bin/sh.

Application

The question asks only for the character that begins this first-line marker. In #!, the leading character is #, so the required character is #.

Contrast

• &: a shell control operator commonly used to run a command asynchronously.

• !: used for history expansion in shells that enable that feature.

• $: introduces parameter or command expansion.

• #: the leading character of the #! interpreter directive.

Cross-check

A typical first line is #!/bin/sh. Reading it from left to right confirms that # is the first character and ! is the second.