Created SC3040 (markdown)

SC3040.md

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+## In POSIX sh, set option pipefail is undefined.
+
+### Problematic code:
+
+```sh
+#!/bin/sh
+set -o pipefail
+if cmd1 | cmd2 | cmd3
+then
+  echo "Success"
+fi
+```
+
+### Correct code:
+
+```sh
+fail="$(mktemp)"
+if { cmd1 || echo > "$fail"; } |
+   { cmd2 || echo > "$fail"; } |
+     cmd3 && [ ! -s "$fail" ]
+then
+  echo "Success"
+fi
+rm "$fail"
+```
+
+or switch to a shell that supports pipefail, such as Bash.
+
+### Rationale:
+
+ShellCheck found `set -o pipefail` in a script declare to run with `sh` or `dash`. This feature may not be supported on these shells.
+
+As an alternative, each stage in the pipeline such as `cmd1` can be rewritten as `{ cmd1 || echo > file; }` which will behave as before but now also write the exit code into `file` if the command fails.
+
+If the file has been written to when the pipeline is done, it means one of the commands failed. This is demonstrated in the correct example.
+
+This can obviously be extended with e.g. `echo "cmd1=$?" >> file` if the particular exit codes for particular commands are desired.
+
+### Exceptions:
+
+If the script has already inspected the current shell and determined the option is available, you can [[ignore]] this message.
+
+### Related resources:
+
+* Help by adding links to BashFAQ, StackOverflow, man pages, POSIX, etc!