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Article from Issue 106/2009

Bash 4 Compatibility

Your article on the new Bash version 4.0 (August 2009, pg. 62) refers to the topic of compatibility right at the start, pointing to eight changes introduced for the sake of POSIX compatibility. Chet Ramey also seems to have been referring to this in your interview, when he said that the new version was as downwardly compatible as possible, but version 3.2's behavior was just incorrect in some places.

In version 4.0 of the shell, the $@ and $* parameter lists are fairly inconsistent "semi-variables" (bash -uc 'echo $@' "$@:unbound variable"; but: @=1 @=1: command not found), although this is not mentioned in the COMPAT file.

These changes mark a departure of the new shell from the POSIX standard, which clearly states: "If there are no positional parameters, the expansion of '@' shall generate zero fields [...]."

[...]

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