Perl/Code

In a Linux/Unix environment it has become standard practise to include a special comment in a script's first line, which will direct the command interpreter (shell) where to find the executable, the so-called "hash bang" line. Usually the complete path to the executable is written, thus making this line in the script dependent on the host's file system structure. Example:

#!/usr/bin/perl -w

# script 'tst'

print "Hello, world!\n";

Now, instead of running

$ perl tst

you can run just the script itself:

$ ./tst

which will produce the expected

Hello, world!

This however requires that a valid Perl executable exists in /usr/bin/ or the shell will produce an error. The '-w' option is always recommended, it will direct Perl to produce warnings about unsafe code such as using undeclared variables, and other potential traps.