Advanced Bash−Scripting Guide

Advanced Bash−Scripting Guide
Arrays lend themselves, to some extent, to emulating data structures for which Bash has no native support.
Example 26−8. Emulating a push−down stack
#!/bin/bash
# stack.sh: push−down stack simulation
# Similar to the CPU stack, a push−down stack stores data items
#+ sequentially, but releases them in reverse order, last−in first−out.
BP=100
SP=$BP
Data=
# Base Pointer of stack array.
# Begin at element 100.
# Stack Pointer.
# Initialize it to "base" (bottom) of stack.
# Contents of stack location.
# Must use local variable,
#+ because of limitation on function return range.
declare −a stack
push()
{
if [ −z "$1" ]
then
return
fi
let "SP −= 1"
stack[$SP]=$1
# Push item on stack.
# Nothing to push?
# Bump stack pointer.
return
}
pop()
{
Data=
# Pop item off stack.
# Empty out data item.
if [ "$SP" −eq "$BP" ] # Stack empty?
then
return
fi # This also keeps SP from getting past 100,
#+ i.e., prevents a runaway stack.
Data=${stack[$SP]}
let "SP += 1"
return
}
# Bump stack pointer.
status_report()
# Find out what's happening.
{
echo "−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−"
echo "REPORT"
echo "Stack Pointer = $SP"
echo "Just popped \""$Data"\" off the stack."
echo "−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−"
echo
}
Chapter 26. Arrays 304