Linux issues with variable not resetting throughout loop

Question

I am currently trying to grab the nth line of text out of a file namelist.txt, store it in a variable "name", and write it to EnergyData.txt using "head -n," as shown:

#!/bin/bash

counter=0

for folder in */
do

   counter=$((counter+1))
   name=$(cat namelist.txt | head -n $counter)
   echo $name
   printf $name >> EnergyData.txt
   cd $folder

   for i in */
   do
      cd $i
      ground_state=$(cat aims.out | grep  "Total energy of the DFT" | cut -c 77-94)
      HL_gap=$(cat aims.out | grep "Overall HOMO-LUMO gap" | tail -n 1 | cut -c 30-41 )
      echo "$i G1: $ground_state " >> ../../EnergyData.txt
      echo "$i HOMO-LUMO gap: $HL_gap "  >> ../../EnergyData.txt
      cd ..
   done

   cd ..
   min=$(cat EnergyData.txt | grep "G1" | cut -c 7-24 | sort -n | head -1)
   echo $min
   minline=$(cat EnergyData.txt | grep "$min" | cut -c 1-25 )
   echo -e "min energy: $minline\n" >> EnergyData.txt

done


Instead of grabbing just the nth line, it grabs the 1st-nth line, pasting progressively more lines as the loop continues. Any advice on how to fix this problem?

This feels like you're halfway through something that might not be the best approach to begin with - instead of reading the entire file for each line, do you maybe want to read it just once, line by line, as in [BashFAQ/001](https://mywiki.wooledge.org/BashFAQ/001)? — Benjamin W., Jun 14 '21 at 23:13
@BenjaminW. I am trying to insert the name in between the other blocks of data gathered in the nested for loop, so it's important that I read the file over every iteration of the for loop. — ogclifford, Jun 14 '21 at 23:29
Run your script through shellcheck: https://www.shellcheck.net/ — , Jun 14 '21 at 23:46
Does this answer your question? [Bash tool to get nth line from a file](https://stackoverflow.com/questions/6022384/bash-tool-to-get-nth-line-from-a-file) — pjh, Jun 15 '21 at 22:29

score 0 · Answer 1 · answered Jun 15 '21 at 19:44

You may want to use awk command to print the specific line that you want, you can pass the counter as a variable with the -v flag, for example:

awk -v count=$counter 'NR==count {print}' namelist.txt

and you can print the line and adding it to the file EnergyData.txt at the same time with:

awk -v count=$counter 'NR==count {print}' namelist.txt | tee -a >> EnergyData.txt

awk is designed to process the file line by line so you may want to exit after processing the line that you want, so try this:

awk -v count=$counter 'NR==count {print; exit;}' namelist.txt | tee -a >> EnergyData.txt

Linux issues with variable not resetting throughout loop

1 Answers1