#11 Consider set -o pipefail a bashism

[mcandre]

Okay, here's a neat one. "set" is a common command in shell scripting languages. In bash and bash-like languages, "set -euo pipefail" enables runtime options that are helpful for debugging, such as -e: exiting immediately when one of the commands in the script fails, -u: treating undefined variables as an error, and -o pipefail: treating a failing program piped to another program as a failure result for the aggregation of piped commands.

The fish program also accepts -e and -u flags, but not -o pipefail, and of course -e and -u mean something different to fish than to bash. So set -o pipefail is really specific to bash.

For what it's worth, ksh and zsh do support set -euo pipefail, though dash only supports set -eu. So set -eu runs as a pseudobashism, and set -euo pipefail, set -o pipefail, or set -e -u -o pipefail are all variants on ways to invoke a command configuration that only succeeds in bash and bash-inspired shells. If your scripts have a habit of using a shebang like #!/bin/sh, /bin/sh could refer to any number of POSIX-y shells, depending on the operating system setup. Any scripts that use bash-specific flags for the set command are not portable to systems without /bin/sh acting as /bin/bash. Accordingly, such scripts should use the more specific shebang #!/bin/bash, in case they are mistakenly run in an environment where /bin/sh maps to /bin/dash, /bin/csh, and so on.

So, would it be possible to warn when a script might invoke set -euo pipefail or similar? If the check is done carefully, it can help to identify scripts that might not be portable to other shell languages.