Question

Is there an idiomatic analog to Ruby’s Object#tap for Unix command pipelines?

Use case: within a pipeline I want to execute a command for its side effects but return the input implicitly so as to not break the chaining of the pipeline. For example:

echo { 1, 2, 3 } |
  tr ' ' '\n' |
  sort |
  tap 'xargs echo' | # arbitrary code, but implicitly return the input
  uniq

I’m coming from Ruby, where I would do this:

[ 1, 2, 3 ].
  sort.
  tap { |x| puts x }.
  uniq

Answer 1

The tee command is similar; it writes its input to standard output as well as one or more files. If that file is a process substitution, you get the same effect, I believe.

echo 1 2 3 | tr ' ' '\n' | sort | tee >( **code** ) | uniq

The code in the process substitution would read from its standard input, which should be the same thing that the call to uniq ends up seeing.