Why source command doesn't work with process substitution in bash 3.2?

Question

I've the following shell script:

cat <(echo foo)
source <(echo bar=bar)
echo $bar

However it works differently in GNU bash 3.2 and 4.3 as shown below:

$ /bin/bash foo.sh 
foo

3.2.53(1)-release

$ /usr/local/bin/bash foo.sh 
foo
bar
4.3.33(1)-release

Why this works only on one version? Is it a bug or added feature?

It seems the process substitution works fine, however problem lay when sourcing the file.

If this is expected behaviour, what other syntax should I use instead to source something from the standard input to be compatible between different bash versions?

Accusal

Duplicate of #10521105 ? – Deidredeific

Answer 1

This is a known limitation in bash 3.2. To work around it:

source /dev/stdin <<<"$(echo bar=bar)"

...or, similarly:

source /dev/stdin <<<"$(cat <(...))"

Deidredeific

eval behavior is not quite identical; look at top-level return semantics, for example, or the various arrays used to stack-trace reporting. – Deidredeific

Amazing! This also works with curl: source /dev/stdin <<<"$( curl $url )" – Castleman

This limitation still exists in GNU bash 4.4.19(1). – Ancilla

@ChadSkeeters, I don't believe that's true. Sure you aren't on a platform, like msys2 Windows builds, with broken process substitutions? See it working fine with bash 5 at ideone.com/amkRVh; if I could link to an online 4.x sandbox I'd do so as well, but the one I know offhand is only IRC vs web-based. – Deidredeific

@CharlesDuffy I'm on MacOS 10.15.4 with bash 4.4.19(1) from brew. Process substitution did not work for me. – Ancilla

@ChadSkeeters, I don't use/trust/condone Homebrew (making /usr/local contents user-writable strikes me as a horrifically bad idea), but I can't reproduce that. Connect to irc.freenode.org, join the channel #evalbot, and run 43# source <(echo bar=bar); echo "$bar" to test in bash 4.3.46(1), or 44# source <(echo bar=bar); echo "$bar" to test in bash 4.4.46(1). Both work fine, emitting bar instead of the empty string. – Deidredeific

@ChadSkeeters, ...I suspect that even though you installed bash 4.4 in Homebrew, that your interactive shell is still Apple's 3.2.57(1). Be sure you're running echo "$BASH_VERSION" to check your active version, not bash --version. – Deidredeific

@CharlesDuffy Good catch. My system's bash shell is 3.2.57(1)-release even though I have a newer version installed via brew. My mistake. – Ancilla