how to merge two files consistently line by line

Question

I have two files (file1.txt & file2.txt ) , files are only examples .

How to merge the two files , in order to create the file - merge_files.txt as example 3

I writing now ksh script , so merge can be done with ksh,awk,sed,perl one liner ...etc

Background - why I need to merge the files : my target is to rename the OLD file (exist in first field) to NEW file (exist in second field) ,

example1

more file1.txt

/etc/port1-192.9.200.1-255.555.255.0
/etc/port2-192.9.200.1-255.555.255.0
/etc/port3-192.9.200.1-255.555.255.0
/etc/port4-192.9.200.1-255.555.255.0
/etc/port5-192.9.200.1-255.555.255.0
.
.
.
.

example2

more file2.txt

/etc/port1-192.90.2.1-255.555.0.0
/etc/port2-192.90.2.1-255.555.0.0
/etc/port3-192.90.2.1-255.555.0.0
/etc/port4-192.90.2.1-255.555.0.0
/etc/port5-192.90.2.1-255.555.0.0
.
.
.
.

example3

 more merge_files.txt



 /etc/port1-192.9.200.1-255.555.255.0  /etc/port1-192.90.2.1-255.555.0.0
 /etc/port2-192.9.200.1-255.555.255.0  /etc/port2-192.90.2.1-255.555.0.0
 /etc/port3-192.9.200.1-255.555.255.0  /etc/port3-192.90.2.1-255.555.0.0
 /etc/port4-192.9.200.1-255.555.255.0  /etc/port4-192.90.2.1-255.555.0.0
 /etc/port5-192.9.200.1-255.555.255.0  /etc/port5-192.90.2.1-255.555.0.0
 .
 .
 .
 .
 .

example4 (merge_files.txt structure)

 first field                           second field

 OLD file                              NEW file

Answer 1

You can use paste to format the files side by side:

$ paste -d" " file1.txt file2.txt
/etc/port1-192.9.200.1-255.555.255.0 /etc/port1-192.90.2.1-255.555.0.0
/etc/port2-192.9.200.1-255.555.255.0 /etc/port2-192.90.2.1-255.555.0.0
/etc/port3-192.9.200.1-255.555.255.0 /etc/port3-192.90.2.1-255.555.0.0
/etc/port4-192.9.200.1-255.555.255.0 /etc/port4-192.90.2.1-255.555.0.0
/etc/port5-192.9.200.1-255.555.255.0 /etc/port5-192.90.2.1-255.555.0.0

E.g.:

$ paste -d" " file1.txt file2.txt | while read from to; do echo mv "${from}" "${to}"; done
mv /etc/port1-192.9.200.1-255.555.255.0 /etc/port1-192.90.2.1-255.555.0.0
mv /etc/port2-192.9.200.1-255.555.255.0 /etc/port2-192.90.2.1-255.555.0.0
mv /etc/port3-192.9.200.1-255.555.255.0 /etc/port3-192.90.2.1-255.555.0.0
mv /etc/port4-192.9.200.1-255.555.255.0 /etc/port4-192.90.2.1-255.555.0.0
mv /etc/port5-192.9.200.1-255.555.255.0 /etc/port5-192.90.2.1-255.555.0.0

Of course you would want to throw in some safety checks ([ -f "${from}" ], ...).

Disclaimer: Works only if there are no spaces in your filenames.