A blog and website by Peter Bengtsson

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How to intercept and react to non-zero exits in bash

Bash, GitHub

Inside a step in a GitHub Action, I want to run a script, and depending on the outcome of that, maybe do some more things. Essentially, if the script fails, I want to print some extra user-friendly messages, but the whole Action should still fail with the same exit code.

In pseudo-code, this is what I want to achieve:

exit_code = that_other_script()
if exit_code > 0:
    print("Extra message if it failed")

So here's how to do that with bash:

# If it's not the default, make it so that it proceeds even if 
# any one line exits non-zero
set +e

./script/update-internal-links.js --check

if [ $exit_code != 0 ]; then
  echo "Extra message here informing that the script failed"
  exit $exit_code

The origin, for me, at the moment, was that I had a GitHub Action where it calls another script that might fail. If it fails, I wanted to print out a verbose extra hint to whoever looks at the output. Steps in GitHub Action runs with set -e by default I think, meaning that if anything goes wrong in the step it leaves the step and runs those steps with if: ${{ failure() }} next.

Please post a comment if you have thoughts or questions.

How to count the most common lines in a file

Bash, MacOSX, Linux

tl;dr sort myfile.log | uniq -c | sort -n -r

I wanted to count recurring lines in a log file and started writing a complicated Python script but then wondered if I can just do it with bash basics.
And after some poking and experimenting I found a really simple one-liner that I'm going to try to remember for next time:

You can't argue with the nice results :)

▶ cat myfile.log

▶ sort myfile.log | uniq -c | sort -n -r
   4 one
   2 two
   1 three
   1 once

Please post a comment if you have thoughts or questions.

Find the largest node_modules directories with bash

Bash, MacOSX, Linux

tl;dr; fd -I -t d node_modules | rg -v 'node_modules/(\w|@)' | xargs du -sh | sort -hr

It's very possible that there's a tool that does this, but if so please enlighten me.
The objective is to find which of all your various projects' node_modules directory is eating up the most disk space.
The challenge is that often you have nested node_modules within and they shouldn't be included.

The command uses fd which comes from brew install fd and it's a fast alternative to the built-in find. Definitely worth investing in if you like to live fast on the command line.
The other important command here is rg which comes from brew install ripgrep and is a fast alternative to built-in grep. Sure, I think one can use find and grep but that can be left as an exercise to the reader.

▶ fd -I -t d node_modules | rg -v 'node_modules/(\w|@)' | xargs du -sh | sort -hr
1.1G    ./GROCER/groce/node_modules/
1.0G    ./SHOULDWATCH/youshouldwatch/node_modules/
826M    ./PETERBECOM/django-peterbecom/adminui/node_modules/
679M    ./JAVASCRIPT/wmr/node_modules/
546M    ./WORKON/workon-fire/node_modules/
539M    ./PETERBECOM/chiveproxy/node_modules/
506M    ./JAVASCRIPT/minimalcss-website/node_modules/
491M    ./WORKON/workon/node_modules/
457M    ./JAVASCRIPT/battleshits/node_modules/
445M    ./GITHUB/DOCS/docs-internal/node_modules/
431M    ./GITHUB/DOCS/docs/node_modules/
418M    ./PETERBECOM/preact-cli-peterbecom/node_modules/
418M    ./PETERBECOM/django-peterbecom/adminui0/node_modules/
399M    ./GITHUB/THEHUB/thehub/node_modules/

How it works:

  • fd -I -t d node_modules: Find all directories called node_modules but ignore any .gitignore directives in their parent directories.
  • rg -v 'node_modules/(\w|@)': Exclude all finds where the word node_modules/ is followed by a @ or a [a-z0-9] character.
  • xargs du -sh: For each line, run du -sh on it. That's like doing cd some/directory && du -sh, where du means "disk usage" and -s means total and -h means human-readable.
  • sort -hr: Sort by the first column as a "human numeric sort" meaning it understands that "1M" is more than "20K"

Now, if I want to free up some disk space, I can look through the list and if I recognize a project I almost never work on any more, I just send it to rm -fr.

Please post a comment if you have thoughts or questions.

Comparing compression commands with hyperfine

Bash, MacOSX, Linux

Today I stumbled across a neat CLI for benchmark comparing CLIs for speed: hyperfine. By David @sharkdp Peter.
It's a great tool in your arsenal for quick benchmarks in the terminal.

It's written in Rust and is easily installed with brew install hyperfine. For example, let's compare a couple of different commands for compressing a file into a new compressed file. I know it's comparing apples and oranges but it's just an example:

hyperfine usage example
(click to see full picture)

It basically executes the following commands over and over and then compares how long each one took on average:

  • apack log.log.apack.gz log.log
  • gzip -k log.log
  • zstd log.log
  • brotli -3 log.log

If you're curious about the ~results~ apples vs oranges, the final result is:

▶ ls -lSh log.log*
-rw-r--r--  1 peterbe  staff    25M Jul  3 10:39 log.log
-rw-r--r--  1 peterbe  staff   2.4M Jul  5 22:00 log.log.apack.gz
-rw-r--r--  1 peterbe  staff   2.4M Jul  3 10:39 log.log.gz
-rw-r--r--  1 peterbe  staff   2.2M Jul  3 10:39 log.log.zst
-rw-r--r--  1 peterbe  staff   2.1M Jul  3 10:39

The point is that you type hyperfine followed by each command in quotation marks. The --prepare is run for each command and you can also use --cleanup="{cleanup command here}.

It's versatile so it doesn't have to be different commands but it can be: hyperfine "python" "python" to compare to Python scripts.

🎵 You can also export the output to a Markdown file. Here, I used:

▶ hyperfine "apack log.log.apack.gz log.log" "gzip -k log.log" "zstd log.log" "brotli -3 log.log" --prepare="rm -fr log.log.*" --export-markdown
▶ cat | pbcopy

and it becomes this:

Command Mean [ms] Min [ms] Max [ms] Relative
apack log.log.apack.gz log.log 291.9 ± 7.2 283.8 304.1 4.90 ± 0.19
gzip -k log.log 240.4 ± 7.3 232.2 256.5 4.03 ± 0.18
zstd log.log 59.6 ± 1.8 55.8 65.5 1.00
brotli -3 log.log 122.8 ± 4.1 117.3 132.4 2.06 ± 0.09

Please post a comment if you have thoughts or questions.

./bin/ - A bash script to prevent lurking ghosts

Python, Linux, Bash

tl;dr; Here's a useful bash script to avoid starting something when its already running as a ghost process.

Huey is a great little Python library for doing background tasks. It's like Celery but much lighter, faster, and easier to understand.

What cost me almost an hour of hair-tearing debugging today was that I didn't realize that a huey daemon process had gotten stuck in the background with code that wasn't updating as I made changes to the file in my project. I just couldn't understand what was going on.

The way I start my project is with honcho which is a Python Foreman clone. The Procfile looks something like this:

elasticsearch: cd /Users/peterbe/dev/PETERBECOM/elasticsearch-7.7.0 && ./bin/elasticsearch -q
web: ./bin/ web
minimalcss: cd minimalcss && PORT=5000 yarn run start
huey: ./ run_huey --flush-locks --huey-verbose
adminui: cd adminui && yarn start
pulse: cd pulse && yarn run dev

And you start that with simply typing:

honcho start

When you Ctrl-C, it kills all those processes but somehow somewhere it doesn't always kill everything. Restarting the computer isn't a fun alternative.

So, to prevent my sanity from draining I wrote this script:

#!/usr/bin/env bash
set -eo pipefail

# This is used to make sure that before you start huey, 
# there isn't already one running the background.
# It has happened that huey gets lingering stuck as a 
# ghost and it's hard to notice it sitting there 
# lurking and being weird.

bad() {
    echo "Huey is already running!"
    exit 1

good() {
    echo "Huey is NOT already running"
    exit 0

ps aux | rg huey | rg -v 'rg huey' | rg -v '' && bad || good

(If you're wondering what rg is; it's short for ripgrep)

And I change my Procfile accordingly:

-huey: ./ run_huey --flush-locks --huey-verbose
+huey: ./bin/ && ./ run_huey --flush-locks --huey-verbose

There really isn't much rocket science or brain surgery about this blog post but I hope it inspires someone who's been in similar trenches that a simple bash script can make all the difference.

Please post a comment if you have thoughts or questions.