What is the general structure of a for loop in a shell script?

The general structure of a for loop in a shell script is typically outlined as "for variable in list; do action; done". This means that a variable will take each value from a specified list, and the actions defined between do and done will be executed for each value.

In the correct choice, the structure explicitly follows this format: a variable named "file" iterates over all files in the current directory that match the pattern "*.txt". The action performed within the loop is the command to echo the value of the variable, which effectively prints the name of each text file.

This format captures both the iteration mechanism and the proper use of the control structure, making it a clear and accurate example of a for loop in a shell script.