Explanation for newbies:

• Shell is the programming language that you use when you open a terminal on linux or mac os. Well, actually “shell” is a family of languages with many different implementations (bash, dash, ash, zsh, ksh, fish, …)

• Writing programs in shell (called “shell scripts”) is a harrowing experience because the language is optimized for interactive use at a terminal, not writing extensive applications

• The two lines in the meme change the shell’s behavior to be slightly less headache-inducing for the programmer:

  • set -euo pipefail is the short form of the following three commands:
    • set -e: exit on the first command that fails, rather than plowing through ignoring all errors
    • set -u: treat references to undefined variables as errors
    • set -o pipefail: If a command piped into another command fails, treat that as an error
  • export LC_ALL=C tells other programs to not do weird things depending on locale. For example, it forces seq to output numbers with a period as the decimal separator, even on systems where coma is the default decimal separator (russian, dutch, etc.).

• The title text references “posix”, which is a document that standardizes, among other things, what features a shell must have. Posix does not require a shell to implement pipefail, so if you want your script to run on as many different platforms as possible, then you cannot use that feature.