While loop doesn't stop (Bash)

Question

I want to get delete all of the blank lines and lines with spaces (if any exist (ONLY from the bottom of the file)) and then to remove one more line (also ONLY from the bottom of the file).

I have this code:

while [[ "$last_line" =~ ^$ ]] || [[ "$last_line" =~ ^[[:space:]]+$ ]]
do
    sed -i -e '${/$/d}' "./file.txt"
done
    sed -i -e '${/$/d}' "./file.txt"

For some reason the loop doesn't stop and it deletes everything in the file. What is the matter?

You're not changing the value of $last_line within the loop, so how could it stop? — Biffen
– Biffen, Commented Aug 5, 2015 at 11:42

anubhava · Accepted Answer · 2015-08-05 12:04:30Z

2

You can use tac and awk combination for this:

tac file | awk 'BEGIN{p=0} p<=1 && /^[[:blank:]]*$/{p=1; next} p==1{p++; next} 1' | tac

tac file         # prints files in reverse
/^[[:blank:]]*$/ # will find all blank/empty lines using search pattern    
tac              # reverse the file content

edited Aug 5, 2015 at 12:04

answered Aug 5, 2015 at 11:41

anubhava

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3 Comments

Darragh Enright Over a year ago

I never heard of tac before (and it's not on OSX Terminal). So I logged into a linux box and looked up the man page... Basically it's cat in reverse. I guess that is pretty obvious in retrospect :D

anubhava Over a year ago

Hmm I am also on OSX but I have installed all gnu utils using home brew hence tac is there for me.

Darragh Enright Over a year ago

I didn't know that was a package - top tip! I remember having some trouble with some of the BSD-flavoured utils in the past - missing flags etc. Thanks @anubhava

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