Dear community,
how can I create an array from file taking only the 4th field?
out.txt file is something like this:
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
17 18 19 20
So the final array should be:
4 8 12 16 20
With this command I created an array with all the fields, but I need only the 4th one:
arr1=( $(cat out.txt | tr '\n' ' ') )
You are not specifying what shell you use; looks like it's bash; try
$ arr=( $(cut -d" " -f4 test) )
$ echo ${#arr[@]} , ${arr[@]}
5 , 4 8 12 16 20
Yes bash, but the command doesn't work for me 
#!/bin/bash
arr=( $(cut -d" " -f4 out.txt) )
echo ${arr[@]}
result empty array:
# ./test.sh
#
---------- Post updated at 02:59 PM ---------- Previous update was at 02:55 PM ----------
Aaah wait, this because I've not specify the correct out.txt file:
So I have as out.txt:
1234567890 1 1 9876[9876=1]
7634567890 1 1 3456[3456=1]
8934567890 1 4 0123[0123=1];1234[4567=3]
5534567890 1 1 0001[0101=1]
7834567890 1 1 3256[3256=1]
4534567890 1 1 7560[7560=1]
1334567890 1 1 900[0900=1]
0034567890 1 2 9899[9899=2]
And this out.txt file with your command produce an empty array!
Pls try the cut cmd from the keyboard, as well as the echo, and post the results.
your new out.txt:
echo ${arr[@]}
9876[9876=1] 3456[3456=1] 0123[0123=1];1234[4567=3] 0001[0101=1] 3256[3256=1] 7560[7560=1] 900[0900=1] 9899[9899=2]
In bash you can use mapfile:
mapfile -t myarray < <(cut -d" " -f4 file)
--
Bye
The cut commnad reply me with blank space:
cut -d" " -f4 out.txt
#
Try with -f1, -f2, -f3
OR: provide an octal/hexdump of out.txt
You probbly have more than 1 space between each field, try using awk instead of cut:
arr=( $(awk '{ print $4}' out.txt)
echo ${arr[@]}
Of course: if you load the array in a subshell (scripts are run in subshells), how can you have it in the parent shell?
------- EDIT ------------------------------
Sorry, I misread your message: I thought you were running echo outside the script.
--
Bye
Oh YES!!! More space between fields!!! 
Your command works ok, except for the fact you've missed one ')' 
arr=( $(awk '{ print $4}' out.txt) )
echo ${arr[@]}
Thanks all for partecipating! Apreciated!
---------- Post updated at 04:04 PM ---------- Previous update was at 03:12 PM ----------
Guys sorry, whitout opening a new thread, is it possible to put into an array the whole line?
1234567890 1 1 9876[9876=1]
7634567890 1 1 3456[3456=1]
8934567890 1 4 0123[0123=1];1234[4567=3]
5534567890 1 1 0001[0101=1]
7834567890 1 1 3256[3256=1]
4534567890 1 1 7560[7560=1]
1334567890 1 1 900[0900=1]
0034567890 1 2 9899[9899=2]
So the array will be:
arr[0]="1234567890 1 1 9876[9876=1]"
arr[1]="7634567890 1 1 3456[3456=1]"
arr[2]="8934567890 1 4 0123[0123=1];1234[4567=3]"
....
....
Then later I'll take the 4th value and the other one to post-process them....
To put into an array the whole lines of a file:
mapfile -t myarray <file
help mapfile for details.
--
Bye
Note mapfile requires bash 4 is you are still on 3 you may need to use cat:
OLDIFS=$IFS
IFS=$'\n'
arr=( $(cat out.txt) )
IFS=$OLDIFS
It may not be an issue for this data set, but, just in case, I'll mention that this approach deletes newlines since contiguous IFS whitespace is treated as a single delimiter.
If the situation requires preserving lines (including newlines) exactly as they appear in the text file, the following will do it:
while IFS= read -r line; do
arr[${#arr[@]}]=$line;
done
Regards,
Alister
Thanks all for partecipating, I'll keep all your suggestion for future use! 
For now, I'll create 4 array for each row in the output file. This will simplify my post-processing!
Just a question, if I can, mapfile is not present in my bash. This because probably I don't have bash v4.
How can I upgrade to bash v4 ??