In a bash function, how do I get stdin into a variable

Question

I want to call a function with a pipe, and read all of stdin into a variable.

I read that the correct way to do that is with read, or maybe read -r or read -a. However, I had a lot of problems in practise doing that (esp with multi-line strings).

In the end I settled on

function example () {
  local input=$(cat)
  ...
}

What is the idiomatic way to do this?

Answer 1

input=$(cat) is a perfectly fine way to capture standard input if you really need to. One caveat is that command substitutions strip all trailing newlines, so if you want to make sure to capture those as well, you need to ensure that something aside from the newline(s) is read last.

input=$(cat; echo x)
input=${input%x}   # Strip the trailing x

Another option in bash 4 or later is to use the readarray command, which will populate an array with each line of standard input, one line per element, which you can then join back into a single variable if desired.

readarray foo
printf -v foo "%s" "${foo[@]}"