Array not surviving while loop

Shell Programming and Scripting
1

So I'm trying to read datafile into an array, with each line representing one variable in the array. I'm successful at first but somehow it keeps getting erased.

i=0
grep '.*' datafile | while read line
do
	echo $i
	array[$i]=$(echo $line)
	echo ${array[1]} #printing array to make sure it's still there
	(( i++ ))
done

echo ${array[1]} #isn't there anymore

Sooo, do any of you know what's happening?

2

Probably because of pipe. ( that creates sub shell )
and the value of array is not exists in the parent shell.

i=0
while read line
do
 ..
 ..
done < datafile
3

anchal_khare is right !
but why use echo ?

array[$i]=$(echo $line)
# could be
array[$i]="$line"

better with quotes if any special character in $line.

4

Your script is relying on undefined behavior. If you want it to work as is, use ksh instead of bash. Bash made an implementation choice that break your logic.

5

In ksh this would work, but as others have noted one of the intricacies of bash is that the part after the pipe get run in a subshell. You do not need a grep statement and a pipe, you can use an if or case statement inside the loop to filter out empty lines.

If you still need to use a pipe into a while loop in bash you can do this:

i=0
grep '.*' datafile | {
while read line
do
        echo $i
        array[$i]=$(echo $line)
        echo ${array[1]} #printing array to make sure it's still there
        (( i++ ))
done

echo ${array[1]} #isn't there anymore
}
6

You can try this technique for reading the file into an array :

$ cat read_file.sh

i=0
while IFS= read line
do
  set_array="${set_array}array[$i]='${line}';"
  (( i++ ))
done < inputfile
eval ${set_array}

echo "array size=${#array[*]}"
for ((i=0; i<${#array[*]}; i++))
do
   echo "array[$i]=${array[$i]}"
done

$ cat inputfile
First line
Line 2
Last line
$ ./read_file.sh
array size=3
array[0]=First line
array[1]=Line 2
array[2]=Last line
$

Jean-Pierre.