2024-10-03_-_better_error_handling_in_bash

anonymous@undisclosed.example.com (Anonymous) — Thu, 03 Oct 2024 18:34:10 +0000

2024-10-03 - better error handling in bash

when wiring bash scripts i always use set -eu -o pipefail to make sure any error that's not explicitly handled is a hard fault. sometimes it's however hard to find the exact line, thus i usually just preemptively add set -x at the beginning, so that in case sth fails, i have a full context. it works, but it's clearly ugly.

there's however a much nicer way of handling it – with traps.

let's take a sample starting code:

#!/bin/bash
set -eu -o pipefail
 
echo "hello, world"
date
false "this is where we'll fail"
echo "never see me"

the output is enigmatic:

hello, world
Thu Oct  3 20:30:05 CEST 2024

we never made it to the end. in shell $? is 1, so the error is reported, but in a longer script – good luck finding what exactly failed!

here's how to do this in a better way:

#!/bin/bash
set -eu -o pipefail
 
on_error() {
  echo "ERROR: $0:$BASH_LINENO failed with exit code $? on:" >&2
  echo "  $BASH_COMMAND" >&2
}
 
trap on_error ERR
 
# actual script goes here - same as before:
echo "hello, world"
date
false "this is where we'll fail"
echo "never see me"

and now the output is decodable, indeed:

hello, world
Thu Oct  3 20:32:03 CEST 2024
ERROR: ./my_script:14 failed with exit code 1 on:
  false "this is where we'll fail"

now we get both nice output and a foot in the door, when things fail. it's such a nice, simple feature – no idea why it's not a common thing all over the place.

2024-10-03_-_raspi_zero_w_1.x_vs._2

anonymous@undisclosed.example.com (Anonymous) — Sun, 24 Nov 2024 20:20:18 +0000

2024-10-03 - RasPi Zero W 1.x vs. 2

RasPi Zero is a nice, little board running linux. for a simpler tasks, that do require a “real OS”, it's a perfect choice, with an friendly price tag. some time ago i bough RasPi Zero 1.x W for a remote flashing tool (i'll leave out details for another post). i needed WiFi-enabled one, but i was hesitating between series 1.x and 2. 1.x was a bit cheaper, but since it's 32-bit, 1 core and thus far less capable, i figured out it will consume less current and went with this one.

it turned out that i had some issues with connecting to my home WiFi. some APs worked, some did not. so i ended up using external (USB) WiFi card. problem solved. it did cost me an evening to figure out the root cause, though.

since i do have version 2 as well, i decided to give it a shot, too. it connected to all WiFis i have flawlessly. that made me thinking – how much power do i really save by using 1.x instead of 2? here's my results.

RasPi version	workload	[V]	[A]	[W]
1.x	idle	5	0.12	0.6
1.x	apt	5	0.3	1.5
2	idle	5	0.1	0.5
2	apt	5	0.25	1.25

turned out that it does not matter if board is doing sth (1 core) or idling – both cases version 2 is more power efficient, despite being 64-bit (vs. 32-bit 1.x). version 2 is a pure win, at a minimal cost difference.

more over - ASLR is almost worthless on 32-bit system nowadays, so 64-bit version is also a security win.

i still have a couple of RasPis 1.x W on the shelve. will use them over time, for sure. but for new projects version 2 is the way to go. :)

BaSzErr - blog:2024:10:03

2024-10-03_-_better_error_handling_in_bash

2024-10-03 - better error handling in bash

2024-10-03_-_raspi_zero_w_1.x_vs._2

2024-10-03 - RasPi Zero W 1.x vs. 2