Find Match in Csv File

You have a few issues here:

1. you need to set awk's field separator appropriately: by default it is whitespace, whereas your files appear to be delimited by semicolons

2. you are trying to match on a partial field: 4670046 is in a but 46700468915 isn't

3. you seem to be confused about which field you are matching, $1 or $2

If you know that you want to match the first 7 characters, you can try

awk -F ';' '
  NR==FNR {a[$1]=$2; next} {k = substr($1,1,7)} k in a {print $0, a[k]}
' OFS='\t' 2.csv 1.csv

or equivalently

awk '
  BEGIN{FS=";"; OFS="\t"} 
  NR==FNR {a[$1]=$2; next} {k = substr($1,1,7)} k in a {print $0, a[k]}
' 2.csv 1.csv

Ex. given

$ head ?.csv
==> 1.csv <==
46700468915;2000

==> 2.csv <==
4670046;Tele2

then

$ awk 'BEGIN{FS=";"; OFS="\t"} NR==FNR {a[$1]=$2; next} {k = substr($1,1,7)} k in a {print $0, a[k]}' 2.csv 1.csv
46700468915;2000    Tele2

The awk solution should be much faster but here is an example, how to achieve this via bash script, which read each line of 2.csv as -array and then uses sed to do the changes (the if statement is not essential part of the script).

$ cat ./script.sh

#!/bin/bash

TARGET_FILE="./1.csv"
ORIGIN_FILE="./2.csv"

# In order to append new column to a line, comment-out -i.bak
while IFS=';' read -r -a line
do
        if grep -q "${line[0]}" "$TARGET_FILE"
        then
                sed "/^${line[0]}/ s/$/;${line[1]}/" "$TARGET_FILE" #-i.bak
        fi
done < "$ORIGIN_FILE"

echo '-----'

# In order to replace the second column of a line, comment-out -i.bak
while IFS=';' read -r -a line
do
        if grep -q "${line[0]}" "$TARGET_FILE"
        then
                sed -r "s/(^${line[0]}.*\;).*$/\1${line[1]}/" "$TARGET_FILE" #-i.bak
        fi
done < "$ORIGIN_FILE"

Example of usage:

$ cat 1.csv
46700468915;2000
46700568916;3000
46700668917;4000

$ cat 2.csv
4670046;Tele2
4670047;Tele3
4670048;Tele4

$ ./script.sh
46700468915;2000;Tele2
46700568916;3000
46700668917;4000
-----
46700468915;Tele2
46700568916;3000
46700668917;4000