In-place substitution for paste command

Question

When I run the following code

echo '1' > file.txt
echo '2' | paste file.txt - > file.txt

I would expect the content of file.txt be 1 2, because the paste command as it name suggests should put the two strings simply side-by-side. However, it is just 2.

Could anyone of you point me towards additional diagnostics to run in order to pin down the problem.

Why would you use paste? Just echo '2' >> file.txt. Your issue is that you are using > rather than >>. — Questionmark, Apr 20 '15 at 15:33
Thanks a lot for your comment. It was just a minimal example. Actually, I would like to paste multiline output to a multiline file. — Penguin Nurse, Apr 21 '15 at 10:36

score 3 · Answer 1 · answered Apr 20 '15 at 15:32

3

The redirection to file.txt at the end of your paste command is truncating your file before paste has a chance to read it.

Try

echo 2 | paste file.txt - > file2.txt

or if you have sponge installed

echo 2 | paste file.txt - | sponge file.txt

answered Apr 20 '15 at 15:32

Stephen Kitt

434,908

Hi Stephen, thanks for your answer. Both solutions work. Solution 1 has the disadvantage of creating an additional file (maybe that's unavoidable). Solution 2 reduces portability, because it needs additional software to be installed. Your answer is still helpful, though. – Penguin Nurse Apr 21 '15 at 10:38

In-place substitution for paste command

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