Need shell script to read two file at same time and print output in single file


Example I have two files 1) file1.txt 2) file2.txt

File1.txt contains

Aaa
Bbb
Ccc
Ddd
Eee
Fff


File2.txt contains

Zzz
Yyy
Xxx
www
vvv
uuu


I need output file like output.txt

Aaa
Zzz
-----
Bbb
Yyy
----
Ccc
Xxx
----
Ddd
www


please help me any one

There are probably a million better ways to do this...
but here goes...

#!/bin/sh
linecount1=$(wc -l file1.txt | cut -d\  -f 1 )
linecount2=$(wc -l file2.txt | cut -d\  -f 1 )
i=1 j=1
while [ $i -le $linecount1 -a $j -le $linecount2 ]; do
    sed -n -e "${i}p" file1.txt >> output.txt
    sed -n -e "${j}p" file2.txt >> output.txt
    echo "-----" >> output.txt
    i=$(( i + 1 )); j=$(( j + 1))
done

With (g|n|m)awk

awk 'NR==FNR{_[NR]=$0}NR!=FNR{print _[FNR] "\n" $0 "\n---"}' file1 file2

ripat,

I knew there would be a better way, most likely awk.
Here, I try to explain how it works...

awk '
NR==FNR {_[NR]=$0}  
                    # NR is total number of lines read in both files.
                    # FNR is number of lines read, reset for each file.
                    # _[NR] is an array named _ with NR as index.
                    # This loads array with contents of file1,
                    # and ignores file2.
                    
NR!=FNR {print _[FNR] "\n" $0 "\n---"}
                    # This part ignores file1.
                    # For each line in file 2,
                    # Print the corresponding line from the array,
                    # using FNR as index.
                    # then a newline, then the line from file2,
                    # another newline, then the dashes, then another newline.
' file1 file2

That's exactly it.
_ has no special meaning. It's just a fast and, I confess, obfuscated way of writing array names.

Well, maybe. However, awk never hit the memory barrier on my systems even on large test files (1 Mega lines and more). But you are probably right. You could do that by parallel looping through two file handles in perl.

awk '{print;getline < "file1";print $0 "\n---"}' file2

thank you all for quick reply