Basic stream/sed? bash script, perform substring on each line

Question

I know this is basic, but I couldn't find the simplest way to iterate through a file with hundreds of lines and extract a substring.

If I have a file:

ABCY uuuu
UNUY uuuu

...

I want to end up with:

uuuu
uuuu
....

Ideally do a substring

{5} detect at character 5 and output that

Answer 1

You need no sed:

cut -c5-9 yourfile

Answer 2

It would be easier to use cut or awk. Assuming that your fields are separated by a space and you want the second field, you can use:

cut -d' ' -f2 file.txt

awk '{print $2}' file.txt

You can also use cut and awk to extract substrings:

cut -c6- file.txt
awk '{print substr($0,6);}'  file.txt

However, if you really want to iterate through the file and extract substrings, you can use a while loop:

while IFS= read -r line
do
    echo ${line:5}
done < file.txt