Regex in shell fails to evaluate

Installing and Using OpenWrt
1

Identical APs and OWRT builds, shell environment variables and busybox version -

root@pWPW10-1:~# opkg list busy*
busybox - 1.36.1-r2

root@pWPW10-2:~# opkg list busy*
busybox - 1.36.1-r2

root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [0-4] ]] && echo $@
root@pWPW10-1:~#

root@pWPW10-2:~# set -- "a" "b" "c"; [[ $# =~ [0-4] ]] && echo $@
a b c
root@pWPW10-2:~#

And more confusion -

root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [1-4] ]] && echo $@
root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [2-4] ]] && echo $@
a b c
root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [3-4] ]] && echo $@
a b c
root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [0-3] ]] && echo $@
root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [1-3] ]] && echo $@
root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [2-3] ]] && echo $@
a b c
root@pWPW10-1:~# set -- "a" "b" "c"; [[ $# =~ [3-3] ]] && echo $@
a b c
root@pWPW10-1:~#

Suggestions?

2

Standard shell is ash and not bash.
Regex is one of the differences

3
4

This is the standard behavior in almost all shells (following is bash, could be sh or ash or csh): if the glob has no match, return the glob; it it has a match return the expansion.

$ ls l*
layer2-mode.sh  layer2.json     layer3.json

$ echo l*
layer2-mode.sh layer2.json layer3.json

$ ls b*
ls: b*: No such file or directory

$ echo b*
b*

So, where you say apk list something*, you should really always be quoting the glob apk list 'something*' to suppress expansion and let apk do its job. Without quotes it's just "accidentally" working sometimes because there happen to be no files that match.

5

This is not an answer to the question as the snippet clearly illustrates different behaviours in identical ash shells.

6

busybox supports a superset of POSIX/ SUSv4 sh syntax, including some common misconceptions bashisms to ease porting - but only the SUSv4 subset is 'guaranteed' ([[ ...]] is always wrong).

7

'wrong' or not, ash (in the OWRT implementation) supports compound command. And that POSIX exposes support for BREs and EREs with regcomp() in utilities, IMNSHO, 'opens the door' for implementation within [[...]].

And why, returning to the OP, does the shell on an AP correctly evaluate the impure shell command whilst on a different AP, not?

Suggestions?