Monday, July 1, 2024

Python and Perl and Bash (oh my!)

I've been thinking a lot recently about code maintainability, including scripts. I write a lot of shell scripts, usually restricting myself to Bourne shell features, not GNU Bash extensions. I also write a lot of Perl scripts, mostly because I'm a thousand years old, and back then, Perl was the state of the scripting art.

Anyway, it's not unusual for me to write a shell script that invokes Perl to do some regular expression magic. For example, I recently wanted to take a dotted IP address (e.g. "") and convert it into a string of 8 hexadecimal digits representing the network order binary representation of the same (i.e. "0a1d0304"). My kneejerk reaction is this:

HEX=`echo "" | perl -nle 'if (/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/) { printf("%02x%02x%02x%02x\n", $1, $2, $3, $4) } else {die "invalid IP $_\n"'}`

But since maintainability has been on my mind lately, most programmers (especially younger ones) would have a steep Perl learning curve to maintain that. So my second thought was to do it in Bash directly. I haven't done much regular expression processing in Bash, given my habit of staying within Bourne, but really, that habit has outlived its usefulness. Open-source Unix (Linux and Berkley) have relegated other Unixes to rare niche use cases, and even those other Unixes have a way to download Bash. I should just accept that Bash extensions are fair game. Here's my second try:

if [[ "$MCAST_ADDR" =~ $pattern ]]; then
  GRP_HEX=$(printf '%02x%02x%02x%02x' ${BASH_REMATCH[1]} ${BASH_REMATCH[2]} ${BASH_REMATCH[3]} ${BASH_REMATCH[4]})
else echo "invalid IP addr"; exit 1

But even as I feel fairly confident that more programmers would be able to maintain that than the Perl version, I still realize that the vast majority of programmers I've known have very basic shell scripting skills. I'm not sure the Bash version expands the pool of qualified maintainers by much. I think the best that can be said is that a programmer with basic shell scripting skills can learn regular expression matching in Bash a lot faster than learning enough Perl to do it.

So, how about Python?

Well, with some help from Claude, here's a Python one-liner:

HEX=`python3 -c "import sys, ipaddress; print('{:08x}'.format(int(ipaddress.ip_address(sys.argv[1]))))"`

So, not only does this use a language that many programmers know, it also completely avoids regular expressions, which is another uncommon skill among the programmers I've known.


What's a dinosaur to do? I haven't been paid to be a programmer for a lot of years, so the programming I do is mostly for my own entertainment. And dammit, I *like* Perl! I've done enough Python programming to know that ... I just don't like it that much. And let's face it: the code I write is unlikely to be widely used, so who cares about maintainability?

(pause for effect)

I do.

I have standards on how programming should be done. If programming is now largely my hobby, I get the most personal reward by doing it according to my standards. I think it's time for me to say a fond farewell to Perl and bow down to my Python overlords.

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