Purpose of first line #!usr/bin/perl in a Perl Program

When you run a program from your command line, you have certain information that is passed to the shell without you thinking about it. For example, you have a path, which tells the shell where it can look for files that you reference.

When a program runs through the web server as a CGI program, it does not have that path. Any programs that you invoke in your CGI program (like 'sendmail', for example) will need to be specified by a full path, so that the shell can find them when it attempts to execute your CGI program.

A common manifestation of this is the path to the script interpreter (often perl) indicated in the first line of your CGI program, which will look something like: #!/usr/bin/perl