34.1. Bash, version2

#!/bin/bash
# String expansion.
# Introduced with version 2 of Bash.
# Strings of the form $'xxx'
#+ have the standard escaped characters interpreted. 
echo $'Ringing bell 3 times \a \a \a'
 # May only ring once with certain terminals.
echo $'Three form feeds \f \f \f'
echo $'10 newlines \n\n\n\n\n\n\n\n\n\n'
echo $'102円141円163円150円' # Bash
 # Octal equivalent of characters.
exit 0

#!/bin/bash
# Indirect variable referencing.
# This has a few of the attributes of references in C++.
a=letter_of_alphabet
letter_of_alphabet=z
echo "a = $a" # Direct reference.
echo "Now a = ${!a}" # Indirect reference.
# The ${!variable} notation is greatly superior to the old "eval var1=\$$var2"
echo
t=table_cell_3
table_cell_3=24
echo "t = ${!t}" # t = 24
table_cell_3=387
echo "Value of t changed to ${!t}" # 387
# This is useful for referencing members of an array or table,
#+ or for simulating a multi-dimensional array.
# An indexing option (analogous to pointer arithmetic)
#+ would have been nice. Sigh.
exit 0

#!/bin/bash
# resistor-inventory.sh
# Simple database application using indirect variable referencing.
# ============================================================== #
# Data
B1723_value=470 # Ohms
B1723_powerdissip=.25 # Watts
B1723_colorcode="yellow-violet-brown" # Color bands
B1723_loc=173 # Where they are
B1723_inventory=78 # How many
B1724_value=1000
B1724_powerdissip=.25
B1724_colorcode="brown-black-red"
B1724_loc=24N
B1724_inventory=243
B1725_value=10000
B1725_powerdissip=.25
B1725_colorcode="brown-black-orange"
B1725_loc=24N
B1725_inventory=89
# ============================================================== #
echo
PS3='Enter catalog number: '
echo
select catalog_number in "B1723" "B1724" "B1725"
do
 Inv=${catalog_number}_inventory
 Val=${catalog_number}_value
 Pdissip=${catalog_number}_powerdissip
 Loc=${catalog_number}_loc
 Ccode=${catalog_number}_colorcode
 echo
 echo "Catalog number $catalog_number:"
 echo "There are ${!Inv} of [${!Val} ohm / ${!Pdissip} watt] resistors in stock."
 echo "These are located in bin # ${!Loc}."
 echo "Their color code is \"${!Ccode}\"."
 break
done
echo; echo
# Exercises:
# ---------
# 1) Rewrite this script to read its data from an external file.
# 2) Rewrite this script to use arrays,
#+ rather than indirect variable referencing.
# Which method is more straightforward and intuitive?
# Notes:
# -----
# Shell scripts are inappropriate for anything except the most simple
#+ database applications, and even then it involves workarounds and kludges.
# Much better is to use a language with native support for data structures,
#+ such as C++ or Java (or even Perl).
exit 0

#!/bin/bash
# Cards:
# Deals four random hands from a deck of cards.
UNPICKED=0
PICKED=1
DUPE_CARD=99
LOWER_LIMIT=0
UPPER_LIMIT=51
CARDS_IN_SUIT=13
CARDS=52
declare -a Deck
declare -a Suits
declare -a Cards
# It would have been easier to implement and more intuitive
#+ with a single, 3-dimensional array.
# Perhaps a future version of Bash will support multidimensional arrays.
initialize_Deck ()
{
i=$LOWER_LIMIT
until [ "$i" -gt $UPPER_LIMIT ]
do
 Deck[i]=$UNPICKED # Set each card of "Deck" as unpicked.
 let "i += 1"
done
echo
}
initialize_Suits ()
{
Suits[0]=C #Clubs
Suits[1]=D #Diamonds
Suits[2]=H #Hearts
Suits[3]=S #Spades
}
initialize_Cards ()
{
Cards=(2 3 4 5 6 7 8 9 10 J Q K A)
# Alternate method of initializing an array.
}
pick_a_card ()
{
card_number=$RANDOM
let "card_number %= $CARDS"
if [ "${Deck[card_number]}" -eq $UNPICKED ]
then
 Deck[card_number]=$PICKED
 return $card_number
else 
 return $DUPE_CARD
fi
}
parse_card ()
{
number=1ドル
let "suit_number = number / CARDS_IN_SUIT"
suit=${Suits[suit_number]}
echo -n "$suit-"
let "card_no = number % CARDS_IN_SUIT"
Card=${Cards[card_no]}
printf %-4s $Card
# Print cards in neat columns.
}
seed_random () # Seed random number generator.
{ # What happens if you don't do this?
seed=`eval date +%s`
let "seed %= 32766"
RANDOM=$seed
# What are some other methods
#+ of seeding the random number generator?
}
deal_cards ()
{
echo
cards_picked=0
while [ "$cards_picked" -le $UPPER_LIMIT ]
do
 pick_a_card
 t=$?
 if [ "$t" -ne $DUPE_CARD ]
 then
 parse_card $t
 u=$cards_picked+1
 # Change back to 1-based indexing (temporarily). Why?
 let "u %= $CARDS_IN_SUIT"
 if [ "$u" -eq 0 ] # Nested if/then condition test.
 then
 echo
 echo
 fi
 # Separate hands.
 let "cards_picked += 1"
 fi 
done 
echo
return 0
}
# Structured programming:
# Entire program logic modularized in functions.
#================
seed_random
initialize_Deck
initialize_Suits
initialize_Cards
deal_cards
#================
exit 0
# Exercise 1:
# Add comments to thoroughly document this script.
# Exercise 2:
# Add a routine (function) to print out each hand sorted in suits.
# You may add other bells and whistles if you like.
# Exercise 3:
# Simplify and streamline the logic of the script.