#!/usr/bin/perl

use strict;
use Cwd;
use POSIX;
use Sys::Hostname;
use File::Basename;

sub interpolate {
  # heavily borrowed from http://search.cpan.org/~djerius/String-Interpolate-RE-0.03/lib/String/Interpolate/RE.pm
  my ($string, $repls, $opts) = (@_);
  $string =~ s{
    (
      (?:(\\.)(?:\{([^\}]+)\})?)|
      (?:\${(\w+)})
    )
  }{
    my $v;
    my $t = (defined($2)) ? $2 : $4;
    if (exists($repls->{$t})) {
      $v = ref($repls->{$t}) eq 'CODE' ? &{$repls->{$t}}($t,$3) : $repls->{$t}
    } elsif (exists($ENV{$t})) {
      $v = $ENV{$t}
    }
    defined($v) ? $v : $1
  }egx;
  return $string;
}

my $string = '\s\n\u@\h \w \D{%F}\n\t\n\T\n\@\n\A\n\$\n${LANG}\n\q\n${FOO} $ ';

my %repls = (
  '\a' => "\a",
  '\D' => sub { strftime($_[1], localtime) },
  '\e' => "\029",
  '\h' => sub { (split(/\./,hostname()))[0] },
  '\H' => sub { hostname() },
  '\n' => "\n",
  '\r' => "\r",
  '\s' => sub { basename($0) },
  '\t' => sub { strftime('%T', localtime) },
  '\T' => sub { strftime('%I:%M:%S', localtime) },
  '\A' => sub { strftime('%R', localtime) },
  '\@' => sub { strftime('%I:%M %p', localtime) },
  '\u' => sub { getpwuid($>) },
  '\w' => sub { $_ = cwd(); s/$ENV{HOME}/~/ ; return $_; },
  '\W' => sub { (cwd() eq $ENV{HOME}) ? '~' : basename(cwd()) },
  '\$' => $>,
);

print interpolate($string,\%repls) . "\n";