I notice that the hush parameter expansion ${parameter:+word} is
backwards compared to bash.
Here is a test case comparing 'u-boot hush' against 'debian bash'.
It shows that at lines 4 and 8, the results are backwards:
shell command result u-boot hush
result debian-bash
------------------------------------- ---------------------
---------------------
1. var=''
2. echo "\${var} = (${var})" ${var} = ()
${var} = ()
3. echo "\${var:-bbbb} = (${var:-bbbb})" ${var:-bbbb} = (bbbb)
${var:-bbbb} = (bbbb)
4. echo "\${var:+cccc} = (${var:+cccc})" ${var:+cccc} = (cccc)
${var:+cccc} = ()
5. var='aaaa'
6. echo "\${var} = (${var})" ${var} = (aaaa)
${var} = (aaaa)
7. echo "\${var:-bbbb} = (${var:-bbbb})" ${var:-bbbb} = (aaaa)
${var:-bbbb} = (aaaa)
8. echo "\${var:+cccc} = (${var:+cccc})" ${var:+cccc} = ()
${var:+cccc} = (cccc)
The bash manual says at:
https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html
${parameter:+word}
------------------
If parameter is null or unset, nothing is substituted, otherwise the
expansion of word is substituted.
Example:
--------
$ var=123
$ echo ${var:+var is set and not null}
var is set and not null
