Append lines from stdin to a file, but only if they don't already appear in the file.
Outputs new lines to
stdout too, making it a bit like a
tee -a that removes duplicates.
Here, a file called
things.txt contains a list of numbers.
newthings.txt contains a second
list of numbers, some of which appear in
things.txt and some of which do not.
anew is used
to append the latter to
▶ cat things.txt Zero One Two ▶ cat newthings.txt One Two Three Four ▶ cat newthings.txt | anew things.txt Three Four ▶ cat things.txt Zero One Two Three Four
Note that the new lines added to
things.txt are also sent to
stdout, this allows for them to
be redirected to another file:
▶ cat newthings.txt | anew things.txt > added-lines.txt ▶ cat added-lines.txt Three Four
▶ go get -u github.com/tomnomnom/anew