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.
#!/usr/bin/perl -w # script 'tst' print "Hello, world!\n";
Now, instead of running
$ perl tst
you can run just the script itself:
which will produce the expected
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.