Shell Script – How to Concatenate Lines from Two Text Files

shell-scripttext processing

I have two text files of the same length, in order: one of products, the other of comparison products. I'd like the output to be "product;comparison" for each line. Yes I could throw them in a spreadsheet and export as csv, but I'd like to understand how to do it in bash. The two files are supplied as arguments.

#!/bin/bash
file1="$1";
file2="$2";
separator=";";
while read -r product
do
  read -r comp < "$file2";
  echo $product $separator $comp >> temp.txt;
done < "$file1"
tr -d " " < temp.txt | sort > out.txt
rm temp.txt

This gives me all the products with the same comparison product! Eg 

$: cat out.txt
product1;comp1
product2;comp1
product3;comp1

I'm obviously not reading the single line of the comp file properly – what am I doing wrong? How do I read a single line?

Best Answer

If you really want to do it in bash, I'd suggest making use of the -u fd option to read from the two files simultaneously using numbered streams, e.g.

while read -r -u3 product; read -r -u4 comp; do 
  printf '%s;%s\n' "$product" "$comp"
done 3<products.txt 4<comps.txt

However, you could just use the paste utility

paste -d\; products.txt comps.txt
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