Translating csh switch to perl

Question

I am currently translating some scripts from csh to perl. I have come across one script which has the following switch control

#And now some control
set get_command = h
set finish = 0

while (1)

    switch ($get_command)
    case "h":
    case "H":
    set cine_command = ""

cat << EOF
Control synchronised cine by (case insensitive):
  A        - A view data
  B        - B view data
  a        - accelerate
  d        - decelerate
  r        - real time heart rate
  <num>    - rate (frames per second)
  i        - toggle interpolation
  s        - step through (may lose a little synchronisation)
  c        - continue (restart) after stepping
  y        - reverse direction
  h        - help (repeat this)
  f        - finish (quit)
  q        - quit (finish)
  <return> -  quit
EOF

    breaksw

    case "":
    case "f":
    case "F":
    case "q":
    case "Q":
        set cine_command = '-f'
        set finish = 1
    breaksw

    case "a":
        set cine_command = '-a'
    breaksw

    case "d":
    case "D":
        set cine_command = '-d'
    breaksw

    case "r":
        case "R":
        set cine_command = "-t $time_per_frame"
    breaksw

    case "i":
    case "I":
        set cine_command = '-i'
    breaksw

    case "s":
    case "S": 
        set cine_command = "-s"
    breaksw

    case "c":
    case "C":
        set cine_command = "-c"
    breaksw

    case "y":
    case "Y":
        set cine_command = "-y"
    breaksw

    case '[0-9]*':
        set cine_command = "-r $get_command"
    breaksw

    default:
        echo "$get_command ignored"
        set cine_command = ""
    endsw

    if ('$cine_command' != '') then
    select_tv $FIRST_TV
    cine $cine_command
    select_tv $SECOND_TV
    cine $cine_command
    endif

    #
    # If we're stopping then get out of this loop.
    #
    if ($finish) break

    echo -n "cine > "
    set get_command = $<

end

I have Perl 5.8.8 installed on my system and using use Strict;which I know may become deprecated in the next perl release, I have tried the following

#Add some fine control to script
my $get_command = 'h';
my $finish = 0;
my $cine_command;

while(<>)
  {
      switch ($get_command)
      {

    case [hH] {$cine_command = "";}

    print STDOUT << 'END';
Control synchronised cine by (case insensitive):
  A        - A view data
  B        - B view data
  a        - accelerate
  d        - decelerate
  r        - real time heart rate
  <num>    - rate (frames per second)
  i        - toggle interpolation
  s        - step through (may lose a little synchronisation)
  c        - continue (restart) after stepping
  y        - reverse direction
  h        - help (repeat this)
  f        - finish (quit)
  q        - quit (finish)
  <return> -  quit
END

      case [fFqQ] 
        {
         $cine_command = '-f';
         $finish = 1;
         }

      case "a"
        {
         $cine_command = '-a';
        }

      case [dD]
        {
         $cine_command = '-d';
         }

      case [rR]
        {
         $cine_command = "-t $time_per_frame";
         }

      case [iI]
        {
         $cine_command = '-i';
         }

      case [sS]
        {
         $cine_command = '-s';
         }

      case [cC]
        {
         $cine_command = '-c';
         }

      case [yY]
        {
         $cine_command = '-y'
         }

      case /\d/
        {
         $cine_command = "-r $get_command";
        }

      else 
        {
          print "$get_command ignored\n";
          $cine_command = "";
          }

    if ($cine_command ne "") 
      {
        `select_tv $FIRST_TV`;
        `cine $cine_command`;
        `select_tv $SECOND_TV`;
        `cine $cine_command`;
      }

    exit if( $finish == 1);

    print STDOUT "cine > \n";
    chomp(my $get_command = <STDIN>);

      }


  }

When I press return I get the required options printed to the terminals. However, when I type any option into STDIN - e.g a, h or d - I get no response. When I enter retirn - I get the message "h ignored" printed to the terminal as expected.

Any ideas?

Answer 1

To those who say Get a newer version of Perl): Not everyone has control over their systems. If the OP is on Red Hat, it's probably a company machine which means the OP doesn't have control over it. The latest releas of Perl on Redhat is 5.8.8. We might consider it antique and obsolete, but many corporate version of Perl use it.

I have the latest and greatest versions of Perl on my local machines that I control, but I have to write using Perl 5.8.8 syntax, and I have to assume I can't download any CPAN modules.

This is real life, and it can suck. But, you have to live with it...

---

First off, Perl and Csh are two completely languages and doing a line-by-line translation of any language into another is not a good idea. Perl is a much more powerful language, and it might be nice to use many of the features to improve your csh script.

If you are parsing a command line, look into using the module Getopts::Long which will do a lot of the work for you and is available in Perl 5.8.8. This may do exactly what you're trying to do with the switch statement and take a lot less work and is a lot more flexible.

I would avoid using the switch statement in Perl. It never really worked very well. The new given/when stuff works better, but alas, it's only available since Perl 5.10.

Instead, forget the switch stuff and use an if/elsif structure then case statement:

my $usage =<<USAGE;
Control synchronised cine by (case insensitive):
  A        - A view data
  B        - B view data
  a        - accelerate
  d        - decelerate
  r        - real time heart rate
  <num>    - rate (frames per second)
  i        - toggle interpolation
  s        - step through (may lose a little synchronisation)
  c        - continue (restart) after stepping
  y        - reverse direction
  h        - help (repeat this)
  f        - finish (quit)
  q        - quit (finish)
  <return> -  quit
USAGE

$cine_command;
$finish;
while ( my $command = get_command() ) {
    if   ( $command =~ /^h$/i ) {
        print "$usage\n";
        exit 0;
    }
    elsif ( $command =~ /^(fq)$/i ) {
        $cine_command = '-f'
        $finish = 1
    }
    elsif ( $command =~ /^a$/i ) {
        $cine_command = '-a';
    }
    elsif ...

It's not as elegant as a switch statement, but it does the job and is easy to understand and maintain. Also take advantage of using regular expression matching. For example $command =~ /^(fq)$/i is checking to see if$commandis equal toF,f,q, orQ` all at the same time.

Answer 2

while(<>){} in perl is not equivalent to while(1)in csh. while(<>) in perl is equivalent to while(defined($_ = <>)) which is a read and a check to see that eof has not been reached. try replacing while(<>) with while(1).

Answer 3

You might look at something like App::Cmd for a larger program with lots of options. Otherwise, a hash of subrefs might work for delegation rather than a switch statement.