Day 10: ls -l *

sean2024 — Thu, 28 Nov 2024 18:39:58 +0000

Introduction

Hey all. I was recently asked this question:

describe what happens when ls -l * is run on the Linux command line

My description was very wrong. But, now that I've got some time and room to learn a bit more, I've taken a few minutes to write up the actual answer.

Listing in Bash on Linux

The Actual Output

Here's an example of the output:

➜  pwd $ ls -l *
-rw-r--r--@ 1 user  group    0 Month 01 14:05 LICENSE
-rw-r--r--@ 1 user  group  202 Month 01 14:05 go.mod
-rw-r--r--@ 1 user  group  896 Month 01 14:05 go.sum
-rw-r--r--@ 1 user  group  138 Month 01 14:05 main.go

cmd:
total 8
-rw-r--r--@ 1 user  group  1444 Month 01 14:05 root.go

internal:
total 16
-rw-r--r--@ 1 user  group   37 Month 01 16:05 main.go
-rw-r--r--@ 1 user  group  225 Month 01 14:10 main_test.go

Here are some things we see so far:

It shows the current working directory and all its non-hidden contents.
It shows permissions of the files in symbolic notation (as opposed to file mode notation like 0755). These permissions include owner, group, and other permissions (in that order) along with @ indicating extended attributes like for SELinux.
It shows the total number of child elements below each directory child below the current working directory (pwd).
This listing shows the user and group indicated on the child (file or dir)
The last mod date/time for the file.

How does `ls` get this information?

stat - for getting file and directory info for each item listed, even with symbolic links and not using the -l (long-listing) option.
lstat - for getting metadata information for when using -l (long-listing) on symbolic link file types.

Code Sample

In an attempt to implement ls with -l support in go, here is a code sample.

What were the difficult parts?

Mode Parsing - Here's the stat_t mode parsing section. The hardest part here was to find the right order of parsing. Some of these file types are also other file types.
User Lookup - It turns out that some user lookups fail. That was annoying, so I had to fail over to "unknown".
Permissions - Parsing permissions so that it was understandable in the application layer was an interesting challenge. Mostly it was difficult to explain through well-named variable names the concept of single integer values being used to represent a series of values. This is interesting as a single integer can be converted to binary and be used to indicate enum values within range of the original value's binary equivilent. There were two operations that I ended up using to read the binary values:

bit shifting to the right (>>) - This removed the parts of the binary value of the original int so that the resulting shifted value can be &-ed with the offset of the part of the original value that we are looking for.
bit is set via bitmask (&) - When the value is shifted to the right so that the resulting value when v & offset == offset.

Symbolic Link De-referencing - The interesting part here was checking for link loops and then having a test confirming successful detection.

Conclusion

In all, this experiment was very informative. Learning how to parse integer values with bit-wise offsets and then to apply bit-mask in order to determine if a value is set is an interesting and efficient technique.

Day 2: Leetcode

sean2024 — Wed, 20 Nov 2024 04:55:20 +0000

Hey everyone!

I'm thrilled to share that I've embarked on a journey to level up my coding skills, and today marks Day 2 of this adventure. 🎉

My Study Goals

Solve 3-9 Medium to Hard Leetcode Problems Daily
Pushing myself with challenging problems to sharpen my problem-solving abilities.
Deep Dive into Each Problem
Not just aiming for the correct answer but truly understanding the underlying concepts and multiple solution approaches.

Dedicated Study Time

2 Hours Daily on coding problems.
2 Hours Weekly on system design to broaden my architectural knowledge.
2 Hours Weekly on a personal project:
- Possibly developing a library that could benefit my team at work (unrelated to actual work projects).
- Alternatively, creating something to deepen my understanding of the network layer.

The Coin Jar Motivation

To keep myself motivated, I've started a fun ritual. For every problem I solve, I drop a coin into a jar. My monthly goal is to fill up the jar each quarter (no pun intended). It's a tangible way to visualize my progress and stay committed. Plus, who doesn't love the satisfying clink of a coin dropping after cracking a tough problem?

Why I'm Sharing This

I believe that documenting and sharing my journey will...

Hold Me Accountable - Knowing that others are following along encourages me to stay on track.
Help Others - Maybe my experiences, struggles, and triumphs can inspire or assist someone else on a similar path.
Build Community - I'd love to connect with others who are also preparing for interviews or looking to improve their skills. ## Looking Ahead

I'm excited about this effort, and I know that consistency is key. I'll be sharing regular updates on my progress, insights from the problems I tackle, and any tips or resources I find helpful.

DEV Community: sean2024