First encouter

• Type in the following perl script (e.g., emacs hw.pl).

  #!/usr/bin/perl -w
  print ("5 beer, please.\n");
  exit;
  

• Now, from the shell (command line terminal), turn on the executable bits.

  $ chmod +x hw.pl
  $ ls -l
  -rwxr-xr-x  1 ntakebay ntakebay 45 Apr  9 20:00 hw.pl
  

  Remember the unix permissions? To run a script, the file has to be executable (x). When you compile a C program, gcc automatically make the object code executable. But we have to manually change the permission mode by chmod command for perl script. If you use minus sign (chmod -x hw.pl), the executable bit get unset.

  chmod u+w file	user who owns it can write
  chmod o+r file	other people can read
  chmod ugo-wx file	user, group, and others cannot write or execute
  chmod -wx file	same as above

• To run it, type ./hw.pl

• With perl, you do not need to compile.
  Actually, it gets compiled each time when you run it (behind the scene).

• The first line starting from #! tells that the script should be ``interpreted'' by a ``perl interpreter'' program /usr/bin/perl.

  The perl interpreter program perl is usually installed at this location in linux and mac OS-X. But in other unix system, you may find it to be installed in /usr/local/bin/perl. Then the first line should be ``#!/usr/local/bin/perl''.

  To find the location of the perl interpreter, try
     which perl

• -w tells that the perl interpreter will print out extra warnings (easier to catch bugs).

• As in C, each statement is terminated by a semi-colon (;).

• Text string is surrounded by double-quotes (").

• The parentheses for built-in functions (e.g., print) are never required nor forbidden. So the following is OK:

  print "5 beer, please.\n";
  

  You'll notice that things are more relaxed (flexible) in perl than in C in general.