Any file name can be used for source-file . Self-contained awk scripts are useful when you want to write a program which users can invoke without knowing that the program is written in awk . If you omit the quotes, only a shell wizard can predict the result. The first line, which starts with a colon, is used so that this shell script will work even if invoked by a user who uses the C shell. A comment is some text that is included in a program for the sake of human readers, and that is not really part of the program.
Comments can explain what the program does, and how it works.
Nearly all programming languages have provisions for comments, because programs are hard to understand without their extra help. The awk language ignores the rest of a line following a sharp sign. But sometimes statements can be more than one line, and lines can contain several statements. A newline at any other point is considered the end of the statement. This is allowed absolutely anywhere in the statement, even in the middle of a string or regular expression.