How to produce the same string for x number of lines and paste 2 files? unix

Question

How to produce the same string for x number of lines and then use paste to combine the files: I have a file as such with unknown number of lines, e.g.:

$ echo -e "a\tb\tc\nd\te\tf" > in.txt
$ cat in.txt
a   b   c
d   e   f

I want to concat the files with a new column that has the same string for every row. I have tried using echo to create a file and then using paste to concat the columns but i have to know the number of rows in in.txt first and then create a in2.txt using echo.

$ echo -e "a\tb\tc\nd\te\tf" > in.txt
$ cat in.txt
a   b   c
d   e   f
$ echo -e "x\nx\n" > in2.txt
$ paste in.txt in2.txt
a   b   c   x
d   e   f   x

How else can I achieve the same output for an unknown number of lines in in.txt?, e.g.

[in:]

a   b   c
d   e   f

[out:]

a   b   c   x
d   e   f   x

My data consist of a million lines with 3 columns in in.txt of 50-200 chars for each line, so solution needs to keep the "big" data size in mind.

Answer 1

One way with join:

echo | join input - -a 1 -o "1.1 1.2 1.3 2.1" -e x

Though just doing a sed replace should be much better.