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Garcia16 · 09-24-2010, 05:38 AM

Hi,

there is some code :

Code:

test=(1 2 3 4 5)

for car in ${test[@]}
do
 echo "Element : $car"
 if [ $car -eq 1 ]
 then
  test=( "${test[@]" 6 )
 fi
done

The idea of above code is that if variable $car equals 1, new element is added "6" to an array. But i don't know why when i am printing
all elements of this array (echo "Element : $car") this element ("6") is not mentioned, but if i make a command which check an amount of contained elements by array it will be 6 elements.

I was wondering about using while command but it is not easy.

Do you have an idea how use this element ("6") which was added before.

GrapefruiTgirl · 09-24-2010, 06:11 AM

Code:

test=(1 2 3 4 5); x=0

while [ "${test[$x]}" ]; do
  car="${test[$x]}"; echo "Element : $car"
  if [ $car -eq 1 ]; then
    test=( "${test[@]}" 6 )
  fi
x=$((x+1)); done

I believe the problem in your original code was that the for construct was grabbing all elements of the array only once, at the start, and running the loop once for each element; and the fact that an element was added to the array at some later point did not change the number of loops that are done - put simply, you correctly determined that the array was not being checked dynamically to see if there were any more elements that the current one.

The code I show above, using a while loop, seems to do what you wish it to do. Here's a sample output, first with no "1" in the array, and then, with a "1" in the array:

Code:

sasha@reactor: test=(8 2 3 4 5); x=0; while [ "${test[$x]}" ]; do car="${test[$x]}"; echo "Element : $car";  if [ $car -eq 1 ];  then test=( "${test[@]}" 7 );  fi; x=$((x+1)); done
Element : 8
Element : 2
Element : 3
Element : 4
Element : 5

sasha@reactor: test=(1 2 3 4 5); x=0; while [ "${test[$x]}" ]; do car="${test[$x]}"; echo "Element : $car";  if [ $car -eq 1 ];  then test=( "${test[@]}" 6 );  fi; x=$((x+1)); done
Element : 1
Element : 2
Element : 3
Element : 4
Element : 5
Element : 6
sasha@reactor:

DOes that help?

Garcia16 · 09-24-2010, 06:31 AM

Hi,

splendid code with examples of using

Thank you very much.

konsolebox · 09-24-2010, 06:33 AM

Hi Garcia16 and GrapefruiTgirl. Maybe this could help as well:

Code:

test=(1 2 3 4 5)
for (( i = 0; i < ${#test[@]}; ++i )); do
    echo "Element : $car"
    if [[ $car -eq 1 ]]; then
        test=("${test[@]" 6)
    fi
done

GrapefruiTgirl · 09-24-2010, 06:39 AM

Ahh

konsolebox, thanks! Early in the morning here, I overlooked using # to get the number of elements in the array, instead, assuming (bad!) that # was only useful for determining the length of a string variable. Nice one! Your solution is more like what I would have posted, had I not been asleep at the wheel

kurumi · 09-24-2010, 06:59 AM

Code:

for i in ${!test[@]}
do
  if [ ${test[$i]} -eq 1 ] ;then
      .....
  fi
done

konsolebox · 09-24-2010, 07:03 AM

Quote:

Originally Posted by kurumi

Code:

for i in ${!test[@]}
do
  if [ ${test[$i]} -eq 1 ] ;then
      .....
  fi
done

Good day kurumi. Does the expanded indices in ${!test[@]} also gets updated when test[] gets a new appended value?

konsolebox · 09-24-2010, 07:19 AM

Quote:

Originally Posted by GrapefruiTgirl

Ahh

konsolebox, thanks! Early in the morning here, I overlooked using # to get the number of elements in the array, instead, assuming (bad!) that # was only useful for determining the length of a string variable. Nice one! Your solution is more like what I would have posted, had I not been asleep at the wheel

When somebody makes a funny quote about wheels it always reminds me about the description that a zodiac book described me.. a free wheeler. Not that I really believe in it but somehow I find the description a bit funny and recalling it always makes me smile a bit.

grail · 09-24-2010, 07:24 AM

So here is another take:

Code:

#!/bin/bash

test=(1 2 3 4 5)

echo ${test[@]}

for car in ${test[*]}
do
    echo "Element : $car"
    (( car == 1 )) && test+=(6)
done

echo ${test[@]}

Edit: Appears I got caught not doing what Grapefruitgirl said

This is the same plan as hers:

Code:

#!/bin/bash

test=(1 2 3 4 5)

echo ${test[@]}

x=0
while [[ ${test[x]} ]]
do
    car=${test[x++]}
    echo "Element : $car"
    (( car == 1 )) && test+=(6)
done

echo ${test[@]}

kurumi · 09-24-2010, 08:49 AM

Quote:

Originally Posted by konsolebox

Good day kurumi. Does the expanded indices in ${!test[@]} also gets updated when test[] gets a new appended value?

Code:

test=(1 2 3 4 5)
echo "before: ${!test[@]}"
for i in ${!test[@]}
do
  if [[ "${test[$i]}" = 1 ]] ;then
      test=(${test[@]} "6")
  fi
done
echo ${test[@]}
echo "after: ${!test[@]}"

konsolebox · 09-24-2010, 10:19 PM

Hello kurumi. The method's also quite valid however the changes should immediately be felt when inside the loop and that number 6 will also be tested if it is equal to 1.

kurumi · 09-24-2010, 10:28 PM

Quote:

Originally Posted by konsolebox

changes should immediately be felt when inside the loop and that number 6 will also be tested if it is equal to 1.

but why should the new value be tested? the original requirement is to append new text to array if element is 1. If you run my script using

Code:

test=(1 2 3 4 5 1)

Code:

$ bash myscript.sh
before: 0 1 2 3 4 5
1 2 3 4 5 1 6 6
after: 0 1 2 3 4 5 6 7

there are two 1's, so there are two 6's. the for loop will not be iterating the new values because in the first place, its only iterating the initial elements.

grail · 09-25-2010, 12:32 AM

Quote:

Originally Posted by kurumi

but why should the new value be tested?

Well I am guessing that is what the OP meant by:

Quote:

Originally Posted by Garcia16

read array dynamically

kurumi · 09-25-2010, 12:54 AM

Quote:

Originally Posted by grail

Well I am guessing that is what the OP meant by:

its a bit strange to me, why there is need to test for "6" against 1, since 6 is only added when the element is 1. ie, why do we need to test what's being added, since we know it couldn't be 1. ?

konsolebox · 09-25-2010, 01:36 AM

At first I also thought that the code was just a shell scripting trial or game.