How is bash scripting affected by the bash4 release?

bash shell bash4

The bash NEWS file, repro'd here with some summary, has some good info. Big new features include:

Associative arrays: name members in array using array[name], and access with ${array[name]}
The special ** glob pattern: match all files and "zero or more" directories
Co-processes: use the coproc keyword to spawn another process, then redirect its I/O to the currently existing shell (or another process, if you so desire)
Case-modifying expansions: match names without regard to character case

bash shell bash4

There is a compatibility document that covers all versions of bash through to 4.1.

Tightening up of POSIX compliance is one area where differences with version 3.2 have arisen.

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