[SOLVED] shell script indexing an array

Garrett85 · 01-04-2013, 04:06 PM

I've got an array CALENDER=(31 28 31 30 31 30 31 31 30 31 30 31)

I have two if statements that Need to get an index from the array above but when I feed a value into the brackets e.g.
${CALENDER[${SECONDDIGIT}]}
or
${CALENDER[${FIRSTDIGIT}]}

it seems to only be getting the first inded of the CALENDER array, 31, even though FIRSTVALUE will have a number from 1-9 in it and SECONDDIGIT will have 10, 11, or 12. Any ideas by I am unable to get the correct index with my FIRST and SECONDDIGIT values? Thanks.

colucix · 01-04-2013, 04:23 PM

It should work, except that arrays indexes are numbered from zero:

Code:

$ CALENDER=(31 28 31 30 31 30 31 31 30 31 30 31)
$ for INDEX in {0..11}
> do
>  echo ${CALENDER[$INDEX]} 
> done
31
28
31
30
31
30
31
31
30
31
30
31
$

Garrett85 · 01-04-2013, 05:00 PM

This looks like a simple loop although I'M new to bash. In my case the index number stored in FIRSTDIGIT & SECONDDIGIT will be bases on user input.

Quote:

Originally Posted by colucix

It should work, except that arrays indexes are numbered from zero:

Code:

$ CALENDER=(31 28 31 30 31 30 31 31 30 31 30 31)
$ for INDEX in {0..11}
> do
>  echo ${CALENDER[$INDEX]} 
> done
31
28
31
30
31
30
31
31
30
31
30
31
$

colucix · 01-04-2013, 05:16 PM

Quote:

Originally Posted by Garrett85

In my case the index number stored in FIRSTDIGIT & SECONDDIGIT will be bases on user input.

How exactly the two variables are assigned? I mean, what is the difference between the two from the user point of view?

By the way, if the input is a number from 1 to 12, you can subtract 1 from it:

Code:

FIRSTDIGIT=$((FIRSTDIGIT - 1))

or simply

Code:

((FIRSTDIGIT--))

or even

Code:

let FIRSTDIGIT=FIRSTDIGIT-1

Another way is to add a dummy value at the beginning of the array so that index 0 can be safely ignored:

Code:

CALENDER=(99 31 28 31 30 31 30 31 31 30 31 30 31)

PTrenholme · 01-04-2013, 05:47 PM

Can you post your code? I suspect that you want to use associative arrays, not numeric indexed ones. Look at the discussion of different array types in pinfo bash for more information.

Garrett85 · 01-04-2013, 07:23 PM

I main problem I'M having is that the value in the index varibles FIRSTDIGIT & SECONDDIGIT are not getting back the correct index from the CALENDER array. I believe that they are always getting the first index in the array. When I run the script with #! /bin/bash -x I see that the indexing varaible is always being checked agaisnt 31, never 28 or 30. If I add a +1 to the FRISTDIGIT it will then be run again 28 which to me is further proof that it the script doesnt seem to care what the value of the indexing variable is but is always going to the first position in the array.
If I run date 04301998 it fails and I don't know why. Below is my code:

Quote:

#! /bin/bash -x

# This is the calender array for the DateValidation program
CALENDER=(31 28 31 30 31 30 31 31 30 31 30 31)

#############################
### FUNCTION-is_leap_year ###
#############################

is_leap_year()
{
PART1=`expr ${YY} % 4`
PART2=`expr ${YY} % 100`
if [[ 0 -eq ${PART1} ]] && [[ 0 -ne ${PART2} ]] || [[ 0 -eq `expr ${YY} % 400` ]]; then #{
result=true
else
result=false
fi #}
}

####################
### END FUNCTION ###
####################

########################
### FUNCTION-get_day ###
########################

get_day()
{
DAY="BAD"
FIRSTDIGIT=${MM:0:1}
SECONDDIGIT=${MM:1:1}
if [[ ${FIRSTDIGIT} -eq 0 ]]; then #{
if [[ ${DD} -gt 0 ]] && [[ ${DD} -le ${CALENDER[${SECONDDIGIT+1}]} ]]; then #{
DAY="GOOD"
fi #}
else
if [[ ${DD} -gt 0 ]] && [[ ${DD} -le ${CALENDER[${MM}]} ]]; then #{
DAY="GOOD"
fi #}
fi #}
}

####################
### END FUNCTION ###
####################

KEEPGOING=1
while [[ ${KEEPGOING} != "exit" ]]; do

read -p "Enter a date for validation: " DATE

# establish the varible LEN to hold the number of characters in Date, 8 is the only valid number
LEN=$(echo ${#DATE})

if [[ "${DATE} == exit" ]]; then
${KEEPGOING}=0

elif [ $LEN -eq 8 ]; then #{

# set date dariables MM, DD, & YY
MM=${DATE:0:2}
DD=${DATE:2:2}
YY=${DATE:4:4}

if [ ${YY} -gt 0 ]; then #{
if [ ${MM} -gt 0 ] && [ ${MM} -lt 13 ]; then
if [ ${MM} -eq 02 ]; then

is_leap_year ${YY}
if [ $result == true ]; then
if [ ${DD} -gt 0 ] && [ ${DD} -le 29 ]; then
echo "${DATE} is a valid date!"
else
echo "${DD} is invalid for this date!"
fi #}
else
get_day ${DD}
if [ ${DAY} == GOOD ]; then
echo "${Date} is a valid date!"
else
echo "${DD} is invalid for this date!"
fi #}
fi #}
else
get_day ${DD}
if [ ${DAY} == GOOD ]; then
echo "${DATE} is a valid date!"
else
echo "${DD} is invalid for this date!"
fi #}
fi #}

else
echo "${MM} is invalid for this date!"
fi #}

else
echo "${YY} is invalid for this date!"
fi #}

else
echo "Invalid number of digits for a date!"
fi #}
done

grail · 01-05-2013, 08:42 AM

Well there are several other errors with the code, but the error with the array is as follows:

Code:

 ${CALENDER[${SECONDDIGIT+1}]}

Here you have included the increment inside the variable call and hence it is being set to 0 and using the first value.

You can simplify this to:

Code:

${CALENDER[SECONDDIGIT-1]}

I would also urge you to look at (()) for testing numbers and review your exit process which does not work.

Garrett85 · 01-05-2013, 01:01 PM

Thanks grail. ${CALENDER[SECONDDIGIT-1]} did it rather than my old ${CALENDER[${SECONDDIGIT-1}]} script. That's been driving me mad for days now. Thanks again.

Quote:

Originally Posted by grail

Well there are several other errors with the code, but the error with the array is as follows:

Code:

 ${CALENDER[${SECONDDIGIT+1}]}

Here you have included the increment inside the variable call and hence it is being set to 0 and using the first value.

You can simplify this to:

Code:

${CALENDER[SECONDDIGIT-1]}

I would also urge you to look at (()) for testing numbers and review your exit process which does not work.