I am working on a labb assn. for class. I have to write a script the replicates the seq. command. I have it working pretty good but if i enter negative number in all three params i go into a infinite loop any help understand where i am going wrong ?????

#!/bin/bash
#Kevin L. Freese
#Week 7 lab

#Display How to message.
HOWTO="How To: Enter <./seq P1 P2 P3> at the command promt "

#Displays the version information.
VERSION="Week 7 Lab. Number Sequencer"

#Make sure user enters three parameters.
[ "$1" = "--version" ] && echo $HOWTO && echo $VERSION && exit
[ "$1" = "--help" ] || [ $# -ne 3 ] && echo "$HOWTO" && exit 1

#Test to make sure user enters correct numbers in the parameters.
[ $1 -gt $3 ] && [ $2 -gt 0 ] && echo "When the starting value is \
greater than the limit, the increment must be negative. Try `seq' --help' \
for more information" && exit 3
[ $1 -lt $3 ] && [ $2 -le 0 ] && echo "When the starting value is \
less than the limit, the increment must be positive. Try `seq' --help' \
for more information" && exit 4

#If the first parameter is less than or equal to the third parameter
#then add the add the fist parameter and the second parameter and
#show sequence.
{ a="$1"; while [ "$a" -le "$3" ]; do echo "$a"; ((a=$a+$2)); done; }

#If the first parameter is less than or equal to the third parameter
#then add the add the fist parameter and the second parameter and
#show sequence.
{ a="$1"; while [ "$a" -ge "$3" ]; do echo "$a"; ((a=$a+$2)); done; }

Just look at your script: you only need one while loop to do the counting. That is the natural way to count. So why are there two loops.

Run it on a piece of paper, without computer.

Q: did you expect that done would terminate the script ?

I'll just give you a hint.

It works fine as is, except, check the punctuation in the two echo statements. Remember that "`" backtics have special meaning in bash.

Also you removed the test to determine if P2 is equal to 0 but you only check for that condidion once, e.g. if P1 > P3 then you dont check P2 for 0 so you could get into a loop.