Full House

My last article about a Bash version change is 10 years old [1]. Version 4 was in the starting blocks at that time, but it took some time for all distributions to switch to this version. Nobody puts their production system at risk without good reason.

Nevertheless, the change was very attractive for developers of complex scripts, because – thanks to associative arrays – a completely new data structure was introduced. The advantages were more elegant, simpler programs that were also easier to maintain. Other important changes included the coproc command (which supports parallelization) and redirection operators.

Treasure Hunt

For Bash 5, the first job is to look at files such as NEWS and CHANGES to separate the important changes from the unimportant ones. These files are linked from the Bash page of maintainer Chet Ramey [2], who – keeping to the true spirit of Bash – almost completely does without graphical elements. The Bash homepage on [3] is in no way inferior (Figure 1). The NEWS file lists 44 changes to Bash and another 11 to the Readline library used since the last stable version. This is information overkill in its purest form.

Figure 1: The Bash homepage – without reference to the 30th anniversary.

On closer inspection, you feel more like a gold digger – the yield in terms of actual nuggets is extremely low. Even for me, and I have written several 10,000 lines of Bash code in the course of my life and exhausted the functionality of Bash in many areas, most of the changes relate to fairly arcane border areas.

One example is associative arrays. In Bash 5, strings consisting only of blanks can also act as keys. This is certainly logical, but not a change that would make you want to migrate prematurely. The new EPOCHSECONDS and EPOCHREALTIME variables are more useful. The first now contains the Unix time (seconds since the beginning of the epoch); the second additionally has the microseconds.

For example, anyone who feeds measurement data into an RRD database every second benefits from this and saves the operating system an additional fork (Figure 2) by not having to call the external Date binary. A list of potentially interesting changes can be found in Table 1.

Figure 2: The new stable Bash ve

Installation

Because of the very manageable number of epochal innovations, installing the new Bash is not really an attractive option. However, if you want to try out Bash 5.0 anyway, you can build the shell yourself. Alternatively, openSUSE's build service offers several experimental and community builds. The problem with these builds, however, is the additional dependency on new glibc versions, so an installation is almost equivalent to a complete update of the whole system.

Users of the rolling release version Tumbleweed offered by openSUSE will find RPM packages for Bash 5.0 and Readline 8 that ensure a simple update path. Arch Linux now also provides a Bash 5.0 package; other well-known Linux distributions are likely to follow soon.

Changes

Given the meager yield of genuine innovations, the question arises as to why the Bash developers changed the major version at all – at the end of the day, it still wasn't quite clear to me either. One potentially decisive hint results from the detailed study of the individual changes. There are also some incompatibilities to the previous version.

Unlike the Linux kernel, changing the version for compatibility reasons is a common procedure for many software projects. If backward compatibility is broken, the team increments the major number. This sometimes leads to the situation where, for years, several versions require active support – Python is a notorious example.

Bash 5.0 basically shows that the scripting language has reached a mature state in the meantime. Like with the last change from Bash 3 to Bash 4, the major distributions will update to the current Bash in upcoming versions and almost no one will notice this change. By then, the worst of the newly-introduced bugs should have been fixed.