Bash – How to add numbers from two txt files with Bash

Maybe you could try to use paste and one additional temp file

touch temp

while read i; do
        awk '{print $4}' ${i}.txt > ${i}_temp
        paste temp ${i}_temp > test.csv
        cp test.csv temp
done < file_list

rm temp

With GNU sed, you can do (even with no extension):

sed -E \
-e 'h;s/(.*)(\.[^.]*$)/\2/;ta;z;:a;x;s//\1/' \
-e 's/([0-9]{1,})/\n000\1\n/g' \
-e 's/\n[0-9]*([0-9]{3})\n/\1/g' \
-e 'G;s/\n//g' file

No loops only regexes.

The first regex will match

• 'h;s/(.*)(\.[^.]*$)/\2/;ta;z;:a;x;s//\1/' place the extension in the hold space (if there was one). Leave the rest in the pattern space.
• 's/([0-9]{1,})/\n000\1\n/g' Place each stream of numbers in separate lines prepending them with 3 zeros.

After each number to modify has been extended to have leading zeros and being in their own line, do:

• 's/\n[0-9]*([0-9]{3})\n/\1/g' Extract the last 3 digits from each line of digits.
• 'G;s/\n//' re-attach the extension captured at the start.

If the source list is:

➤ cat file
1- 23.m2
ATestFile.mp4
SomeFile.m4a
AFileWithNumbers23inside.mp4
File 1 with 12 some 100 numbers 3.mp4
SL Benfica - Match 1 vs FC Porto.mp4
SL Benfica - Match 2 vs FC Porto.mp4
SL Benfica - Match 20 vs FC Porto.mp4
SL Benfica - Match 101 vs FC Porto.mp4

The result will be:

001- 023.m2
ATestFile.mp4
SomeFile.m4a
AFileWithNumbers023inside.mp4
File 001 with 012 some 100 numbers 003.mp4
SL Benfica - Match 001 vs FC Porto.mp4
SL Benfica - Match 002 vs FC Porto.mp4
SL Benfica - Match 020 vs FC Porto.mp4
SL Benfica - Match 101 vs FC Porto.mp4

So, to rename files (filenames should not contain newlines and the extension should follow a dot):

#!/bin/bash

for old in *; do
    new=$(  printf '%s\n' "$old" | 
                sed -E \
                    -e 'h;s/(.*)(\.[^.]*$)/\2/;ta;z;:a;x;s//\1/' \
                    -e 's/([0-9]{1,})/\n000\1\n/g' \
                    -e 's/\n[0-9]*([0-9]{3})\n/\1/g' \
                    -e 'G;s/\n//'
         );
    if [[ ! -f $new ]]; then
        echo \
            mv "$old" "$new";
    fi
done

Remove the echo after you are satisfied with the script to actually change the files.