Hidden gems of moreutils(jpospisil.com)

  You'll never know for sure what shell is the default, so write your scripts to a minimum shell family, and encode the name of that shell family in the shebang.

  - A Bourne shell
  - A C shell
  - A POSIX shell
  - A "modern" shell, like Bash, Zsh, Fish, Osh

  #!/usr/bin/env sh
  #              ^ should result in a Bourne-like shell, on modern systems, but could also be
  #                a POSIX shell (like Ash), which is not really backwards compatible

  #!/usr/bin/env csh
  #              ^ should result in a C shell

  #!/usr/bin/env bash
  #              ^ should result in a Bash shell, though the only version you should
  #                expect is version 3.2.57, the last GPLv2 version

  #!/usr/bin/env dash
  #              ^ you expect the system to have a specific shell. if your code depends
  #                on Dash features, do this. otherwise write your code using an earlier
  #                version of the original shell family, such as Bourne or POSIX.

  - Comparison of command shells[1]
  - Major differences between Bash and Bourne shell[2]
  - Practical differences between Bash and Zsh[3]
  - Fundamental differences between mainstream \*NIX shells[4]

    cat /dev/zero | dd count=10000000 bs=1024 | cat > /dev/null