3 ms·

Bash Is Irrecoverably Broken

account-5 3y ago
2013 - is this still the case 10 years on?
- louisbuchbinder 3y ago
  Yes or at least something similar. TLDR array lookups are not constant time in bash. I tested on my M1 Mac which came with bash3.2 installed and on ubuntu:22.04 with bash5.1. Interestingly bash5.1 seems to be able to traverse in reverse order based on bench65536. ```benchmark.sh #!/bin/bash xs=($(seq 65536)) function bench0() { local x=${xs[0]} y=${xs[0]} } function bench16384() { local x=${xs[16384]} y=${xs[0]} } function bench65536() { local x=${xs[65536]} y=${xs[0]} } function bench() { for n in $(seq 65536); do $1 done } echo bash version: $BASH_VERSION printf '\n%s:' 'bench0: local x=${xs[0]} y=${xs[0]}' time bench bench0 printf '\n%s' 'bench16384: local x=${xs[16384]} y=${xs[0]}' time bench bench16384 printf '\n%s' 'bench65536: local x=${xs[65536]} y=${xs[0]}' time bench bench65536 ``` ```m1mac.txt bash version: 3.2.57(1)-release bench0: local x=${xs[0]} y=${xs[0]}: real 0m0.366s user 0m0.346s sys 0m0.020s bench16384: local x=${xs[16384]} y=${xs[0]} real 0m1.704s user 0m1.676s sys 0m0.028s bench65536: local x=${xs[65536]} y=${xs[0]} real 0m5.443s user 0m5.393s sys 0m0.050s ``` ```docker_ubuntu2204.txt bash version: 5.1.16(1)-release bench0: local x=${xs[0]} y=${xs[0]}: real 0m0.348s user 0m0.345s sys 0m0.005s bench16384: local x=${xs[16384]} y=${xs[0]} real 0m2.394s user 0m2.390s sys 0m0.005s bench65536: local x=${xs[65536]} y=${xs[0]} real 0m0.348s user 0m0.345s sys 0m0.005s ```
shrimp_emoji 3y ago
In Bash's (not that strong) defense, it's a command language. If you're reaching for fancy data structures in it, you've wandered off too far. You're trying to do generic programming in a command language. You're trying to cut a tree with a steak knife. At that point, you should use Python or C or something. It may be the case that command languages are doomed to be terrible general programming languages and general programming languages doomed to be terrible command languages since it seems like that's the case, universally. Therefore, they're totally different niches.

2013 - is this still the case 10 years on?

louisbuchbinder 3y ago
Yes or at least something similar. TLDR array lookups are not constant time in bash. I tested on my M1 Mac which came with bash3.2 installed and on ubuntu:22.04 with bash5.1. Interestingly bash5.1 seems to be able to traverse in reverse order based on bench65536. ```benchmark.sh #!/bin/bash xs=($(seq 65536)) function bench0() { local x=${xs[0]} y=${xs[0]} } function bench16384() { local x=${xs[16384]} y=${xs[0]} } function bench65536() { local x=${xs[65536]} y=${xs[0]} } function bench() { for n in $(seq 65536); do $1 done } echo bash version: $BASH_VERSION printf '\n%s:' 'bench0: local x=${xs[0]} y=${xs[0]}' time bench bench0 printf '\n%s' 'bench16384: local x=${xs[16384]} y=${xs[0]}' time bench bench16384 printf '\n%s' 'bench65536: local x=${xs[65536]} y=${xs[0]}' time bench bench65536 ``` ```m1mac.txt bash version: 3.2.57(1)-release bench0: local x=${xs[0]} y=${xs[0]}: real 0m0.366s user 0m0.346s sys 0m0.020s bench16384: local x=${xs[16384]} y=${xs[0]} real 0m1.704s user 0m1.676s sys 0m0.028s bench65536: local x=${xs[65536]} y=${xs[0]} real 0m5.443s user 0m5.393s sys 0m0.050s ``` ```docker_ubuntu2204.txt bash version: 5.1.16(1)-release bench0: local x=${xs[0]} y=${xs[0]}: real 0m0.348s user 0m0.345s sys 0m0.005s bench16384: local x=${xs[16384]} y=${xs[0]} real 0m2.394s user 0m2.390s sys 0m0.005s bench65536: local x=${xs[65536]} y=${xs[0]} real 0m0.348s user 0m0.345s sys 0m0.005s ```

In Bash's (not that strong) defense, it's a command language. If you're reaching for fancy data structures in it, you've wandered off too far. You're trying to do generic programming in a command language. You're trying to cut a tree with a steak knife. At that point, you should use Python or C or something. It may be the case that command languages are doomed to be terrible general programming languages and general programming languages doomed to be terrible command languages since it seems like that's the case, universally. Therefore, they're totally different niches.