Do not assume a path to the sh and env binaries

[fornwall]

This improves portability, specifically for non-rooted Android devices which lacks /bin and /usr folders.

[tduehr]

This also breaks installs where PATH is scrubbed before this is run. /usr/bin and /bin are standard locations for these binaries in most distributions and it's common practice to hardcode their location. Where are they in Android? A better route will be to detect they're not in the expected location and use a different path.

[fornwall]

This also breaks installs where PATH is scrubbed before this is run.

Do you know of any such install (or have ever encountered one) with sh and env not in PATH, or is it more of a defensive plan?

I have been pushing in some changes in various projects that replaces /bin/sh => sh and /usr/bin/env => env (like in oh-my-zsh and gevent), so would like to know if I'm breaking something there!

Where are they in Android?

There are system binaries in /system/bin/, but the sh implementation varies over Androd devices and is not that reliable as a standard general sh, so in Termux an app-supplied sh is put in an app-private folder (a horrible path of /data/data/com.termux/files/usr/bin/sh).

A better route will be to detect they're not in the expected location and use a different path.

Would something like the below be ok to determine which sh to use? It would only fall back to using PATH if /bin/sh does not exist:

SHELL=/bin/sh
if [ ! -x /bin/sh ]; then SHELL=sh; fi

[tduehr]

/usr/bin/env and /bin/sh are standard locations across Unix like systems. Any widely distributed, mildly cross-platform shell script will use the following shebang:

#!/usr/bin/env [ruby|python|bash|perl|etc]

The assumed shell in every unix-like system I've used is /bin/sh which should be at least compatible with Bourne Shell. A lot of software is unhappy if that is not the case. Usually resulting in a platform specific package and patch.

Fallback to relying on PATH is okay. but it should probably try /system/bin/sh before falling back to PATH.

[polyzium]

I tried it myself locally with Termux, it failed to build:

1 @localhost ~/ffi (git)-[master] % rake gem:install                                                                                                                                                    
rake aborted!
NoMethodError: undefined method `last_comment' for #<Rake::Application:0x00007f9c657ab8>
/data/data/com.termux/files/home/ffi/Rakefile:227:in `new'
/data/data/com.termux/files/home/ffi/Rakefile:227:in `block in <top (required)>'
/data/data/com.termux/files/home/ffi/Rakefile:226:in `<top (required)>'

[tduehr]

Where are sh and env on that device? Would fallback to PATH have fixed it?

[fornwall]

Where are sh and env on that device? Would fallback to PATH have fixed it?

They are under /data/data/com.termux/files/usr/bin/ which is in the PATH so using PATH should fix it.

Would something like this be fine (if the check for certain paths is still desired)?

SH=sh
ENV=env
if [ -x /bin/sh ]; then SH=/bin/sh; fi
if [ -x /usr/bin/env ]; then ENV=/usr/bin/env; fi

And then use $ENV and $SH to execute them?

[tduehr]

Probably just use env vars to override their location. Not sure why I didn't think of that earlier.

Test the env var then test the standard path and finally fall back to PATH.

[fornwall]

@tduehr Like this?

ENV=${ENV:-/usr/bin/env}
SH=${SH:-/bin/sh}

if [ ! -x "$SH" ]; then SH=sh; fi
if [ ! -x "$ENV" ]; then ENV=env; fi

[tduehr]

Yup

[tduehr]

Upon further research...