First encouter

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

  #!/usr/bin/perl -w
  
  print ("5 beer, please.\n");
  
  $drink = "whisky";
  $howmany = 1;
  $howmany = $howmany + 1;
  
  print ("Or $howmany $drink, 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). If you use minus sign (chmod -x hw.pl), the executable bit get unset.

  chmod u+w file	(u)ser who owns it can write
  chmod o+r file	(o)ther people can read
  chmod ugo-wx file	(u)ser, (g)roup, and (o)thers cannot write or execute
  chmod -wx file	same as above

• To run it, type ./hw.pl

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

    If the perl interpreter program perl is not at this location, it might 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).

  • Each statement is terminated by a semi-colon (;).

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

  • A simple variable (= a container/memory to store data) starts with $.
  • I used howmany as the name of the container (variable). But you can give whatever name to each container (e.g. ``$varA'', ``$weight1'').
  • You can change the contents of variables.