How to implement 'set -o pipefail' in a POSIX way - almost done, expert help needed

Question

I have to implement the BASH set -o pipefail option in a POSIX way so that it works on various LINUX/UNIX flavors. To explain a bit, this option enables the user to

Answer 1

Am I missing something?

my-script.sh

#!/bin/sh

set -e

cat app.log | grep 'ERROR' 

printf 'It will never print this.\n'

$ ./my-script.sh
cat: app.log: No such file or directory

Answer 2

When you type:

run echo "test" ; grep "test" \| awk '{print}'

you invoke run with the arguments echo and "test"; then you invoke grep with arguments "test", |, awk and {print}. Typically, grep is not going to find any of the files called |, awk or {print}.

To invoke run as you wanted, you'd have to escape the semi-colon like you did the | (and you'd need to do things similarly for && or || or & and possibly other components of a command line; the handling of $(...) or backticks `...` needs to be thought about carefully).

If you write:

run echo "test" \; grep "test" \| awk '{print}'

you will at least get all the arguments you intended to run. Whether it then works is debatable; I don't yet understand how the run code you showed is supposed to work.

[...Later...]

It does some fearsome I/O redirections, but wraps each segment of a command separated by a pipe symbol into a separate little packet of hieroglyphs. It assumes that wrapping double quotes around an argument neutralizes it correctly, which is not always true (though it is true a lot of the time).

Answer 3

My two cents:

#!/bin/sh

# Saving the pid of the main shell is required,
# as each element of the pipe is a subshell.
self=$$

lots_and_fail() {
    seq 100
    return 1
}

{ lots_and_fail || kill $self; } | sed s/7/3/

This thing seems to do the job. Thoughts?

Answer 4

The core of your idea should probably involve something like this:

{ cmd1 ; echo $? > status1 ; } | cmd2 && grep -q '^0$' status1 }

In longer form, that would be:

{ cmd1 ; echo $? > status1 ; } |  \
{ cmd2 ; echo $? > status2 ; } |  \
  # ... and so on                 \
  cmdN                         && \
  # ^ note lack of wrapper        \ 
grep -q '^0$' status1 &&          \
grep -q '^0$' status2 &&          \
  # ... and so on, to N-1