Required

ex01: print_groups

The easiest way to get a clean list of a user's group is using

id -nG $FT_USER

This will have the output seperated by spaces and ending with a newline, but the exercise requires commas and no newline at the end of output. So how do we fix this?

Using the tr command, we can replace one character with another character. So to replace with ,:

id -nG $FT_USER | tr ' ' ','

And what about the newline? We can remove \n which is the escape sequence for the newline character using tr as well using it's -d parameter

So final command is:

id -nG $FT_USER | tr ' ' ',' | tr -d '\n'

Using the pipe (|) character, we can pass the output of the command to the left of it to the one on the right. So the output basically goes through all 3 of these commands that way.

ex02: find_sh

Using the basename command we can get the filename of a path. Using -s we can remove the .sh suffix (see man page for basename)

But if we want to do it for every file found in the current directory, we need to use find alongside basename as follows:

basename -s ".sh" $(find . -name "*.sh")

The $(...) expression runs the command in the brackets and puts each line of the output in it's place. So this causes every found file to run basename on it and you get the desired result.

ex03: count_files

This counts both how many regular files and regular dirs are in the directory.

Using

find . -type f,d

we can list these files. Notice how every file has its own line? We can use wc (stands for word count) with it's -l parameter to count all the newlines, which there is 1 per file for.

find . -type f,d | wc -l

The result is the number we counted.

ex04: MAC

In UNIX(-like) operating systems, the file system exposes almost everything through "files". Whether it's files, symlinks, hardlinks, system reports or even hardware it's all there and handled by the kernel.

In Linux, /sys/class/net/ contains all the networking related information for all interfaces. Each interface has a "file" called address which contains that network interface's MAC address. So if we cat all address files available, we get every MAC address for that computer.

cat /sys/class/net/*/address

This only works on Linux tho. If that's an issue, I'll correct this solution.

ex05: "\\?\$\'MaRViN'\\$?\\"

To name a file"\\?\$\'MaRViN'\\$?\\" you must put the file name in touch in single quotes, which ignores all special characters

touch '"\?$*’MaRViN’*$?\"'

Note that the ’ does not actually equal ' which is why this works

Then write 42 inside.

Optional

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This page is Shell01's notes, rendered here from the README on GitHub. Last read on 18 October 2026 at 18:37 UTC.