Wolfgang Resch - Notes

Splitting bash pipelines

December 10, 2012


How can you take the same output of a single process and pipe it through more than one other process?


Using a bash-specific trick and tee:

cat foo | tee >(process1) >(process2) | process3

This works since tee can write what it reads on its stdin to several files. This can be combined with the (bash only) process substitution >(process), which makes the process act like a file. This way process1, process2, and process3 all work on the same input. This can be useful, for example, when filtering a file by different criteria and saving compressed output to different files (contrived example below):

zcat foo.fq.gz | tee >(find_reads_with_adaptor | gzip -c > reads_with_adaptor.fq.gz) \
    | find_low_quality_reads | gzip -c > low_quality_reads.fq.gz