Adding different suffix to end of the line

Question

I have a text file which contains this:

John
Jack
Jerry

I have another text file:

2017
2015
2018

And I want to make them like this:

John2017
John2015
John2018
Jack2017
Jack2015
Jack2018
Jerry2017
Jerry2015
Jerry2018

How can I do this?

Answer 1

Assuming that the files are small, it may be viable to read them into arrays (with bash or ksh93):

names=( $( <names.txt ) )
years=( $( <years.txt ) )

You may then construct a double loop that combines each name with each year in turn:

for n in "${names[@]}"; do
  for y in "${years[@]}"; do
    printf '%s%s\n' "$n" "$y"
  done
done

If years.txt is small, but names.txt is large:

years=( $( <years.txt ) )

while read n; do
  for y in "${years[@]}"; do
    printf '%s%s\n' "$n" "$y"
  done
done <names.txt

Result:

John2017
John2015
John2018
Jack2017
Jack2015
Jack2018
Jerry2017
Jerry2015
Jerry2018

Treating the files as single-column, header-less, CSV files:

$ csvsql -H --query "SELECT * FROM names CROSS JOIN years" names.txt years.txt | sed -e '1d' -e 's/,//'

This performs a relational cross join operation on the data in the two tables and then goes on to strip off the first line of the output along with all commas (csvsql creates properly formatted CSV with a header line and comma-separated values).

csvsql is part of csvkit.

Answer 2

$ join -j2 -t : names year | tr -d :

• join by a non existing field and remove the output field separators.

Field 2 is empty and equal for all the element in names and year so join will concatenate each name with all the years: it is in fact calculating the Cartesian product.

Answer 3

The solution that @Kusalananda provided is superior to this one. I provided it without fully thinking through what $(cat ...) does in terms of memory usage. I'll leave it here for reference – it'll work and isn't terrible for if the files are small.

#!/bin/bash

for name in $(cat names); do
    for year in $(cat years); do
        echo "${name}${year}"
    done
done