Basic User Management

Using coreutils on macOS


The date command lets you get the date in your terminal. It contains the -I flag which allows you to get the date in ISO8601 format. -Is to print the ISO8601 date as well as the current time up to seconds.



If you have a process running in the background of your terminal, you can release it. The process will continue, retaining the original PID, but it will no longer be part of your terminal session.

# disown the process with job id %2
disown %2


stat() is a Unix system call that returns file attributes about an inode. 1 The semantics of stat() vary between operating systems. As an example, Unix command ls uses this system call to retrieve information on files that includes:

You can use stat to get information about a file.


The du command stands for disk usage. It can tell you information about how much space a given file on your computer is taking up.

Viewing the size of a directory

You can also set the environment variable DU_BLOCK_SIZE to have a default setting for the size of blocks reported by du


The lsof command stands for list open files. On the surface, this doesn't seem useful, you'd know what files are open on your computer. However, Unix thinks of everything as a file. This includes sockets, ports, etc.


The -m flag allows you to specify the octal permissions code for the files inside the directory to be created.


By default, head will return the first 10 lines of the specified file. You can use the -n flag to specify the number of lines that should be returned.


By default, tail will return the last 10 lines of the specified file. You can use the -n flag to specify the number of lines that should be returned.


Although more people are familiar with the .zip extention written by microsoft, there also exists the GNU zip .gz extension, which has a slightly higher performance benchmark in comarison to .zip.


The Unix dig command, which stands for "Domain Information Groper" is a program used to query DNS servers for the records held by domain names.

dig @ helpful.wiki A +short
# =>


tar is a tool used for archiving files onto tape drives, which is why the program stands for tape archive. Today it is still used to create a compressed copy of a directory. tar is used to create tarballs, a term used to denote an archive .tar file.

Useful flags

Short form Long form Function
-c --create Create a new .tar tarball
-r --append Append files to a existing tarball
-t --list List the contents of a tarball
-u --update Append a file to the archive, even if an existing version of that file is already in the archive
-x --extract Extract the files contained within an archive
N/A --delete Delete the file from the archive
-k --keep-old-files Don't replace existing files when extracting files from an archive
-f --file Specify the archive file to be created, or the one to be extracted from
-z --gzip Filter the archive command through gzip
-a --auto Use the archive file's suffix to automatically determine which compression program to use
-v --verbose Verbosely list files as they are being processed.
-w --interactive Ask for confirmation for every action
-h --dereference Follow any symlinks and archive the files they point to
-C --dir Change to a different directory before performing any operations
-O --to-stdout Extract files to standard output
-P --absolute Don't strip leading slashes from file names when creating an archive
-N --newer Only store files newer than DATE, which, if starting with a / or a . will be calculated in reference to the file specified as DATE.
N/A --utc Print file modification times in UTC
N/A --exclude-vcs Exclude version control systems like .git
N/A --excluse-vcs-ignores Excludes files from VCS ignore files like .gitignore
N/A --overwrite Overwrite existing files when extracting
N/A --remove-files Remove files from the disk after adding them to the archive
N/A --skip-old-files Don't replace existing files when extracting, silently skip over them
N/A --xform / --transform Use sed to replace the following expression when transforming the file names
N/A --strip n Strip n leading components from the file names on extraction
N/A --quoting Specify the style of quoting when listing directory contents, accepts shell as a valid argument

Creating an archive

When creating an archive, the -C or --dir option is very useful. It allows you to specify which directory to be in for the subsequent operations. In the case of archiving a file, by default tar will create the archive including every directory specified in the path. If you tried to type tar -cf archive.tar ~/example then it would actually create an archive of /Users/tommy/example where the root directory is /Users, containing a single directory /tommy, which itself contained a single directory /example. To avoid this, you must specify which directory tar should operate from. In this case, it should be the parent directory of example which is /Users/tommy.


tar -f archive.tar -t
tar --file archive.tar --list
# -> example/spaced out.txt
tar --file archive.tar --list --quoting shell


Getting Started

brew install tree


rs and datamash




Typically, a manpage for a given command is located at /usr/share/man/man1/command.1

sudo update-alternatives /usr/bin/yarn yarn /usr/bin/yarnpkg 1

You can also do the same for python3

sudo apt install python3
sudo apt install python3-pip
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 1
sudo update-alternatives --install /usr/bin/pip pip /usr/bin/pip3 1



File Systems

File System Hierarchy

Volumes & Drives

The collection of non-volatile memory stored on a computer is kept in one or more Volumes. The collection of data is the Volume, and the device this volume exists on is what's known as the Drive. Back in the day, these drives were implemented as discs, hence the term Floppy Disk Drive and Hard Disk Drive. These days, we're moving on from disc drives, instead transitioning to Solid State Drives, which use transistors and circuits to store the volume (which contains the file system).

The commands for performing various operations are different on macOS and Linux. I'll try to include an example of how to do each in the relevant section. (I ran out of time while writing this, so this is to be continued for now...)


PAC Files

A Proxy Auto-Config PAC file contains a JavaScript function that decides which proxy a given network connection (URL) should use. curl does not support PAC files, but I'm putting this note here for now.


Article: Authentication: Everything curl

curl --anyauth \


Example crontab using zsh globbing


# When the computer reboots,
# delete any files in ~/tmp that haven't been accessed in over a day
@reboot rm ~/tmp/**/*(.ad+1) 2> ~/tmp/cron.log

# When the computer reboots,
# delete any directories in ~/tmp that are empty
@reboot rm -rf ~/tmp/**/*(/^F) 2> ~/tmp/cron.log

# Month, Hour, Day, Month, Weekday
#   *     *     *     *       *

# @yearly
0 0 1 1 * echo 'Once a year' &> ~/log.txt

# @monthly
0 0 1 * * echo 'Once a month' &> ~/log.txt

# @weekly
0 0 * * 0 echo 'Once a week' &> ~/log.txt

# @daily
0 0 * * * echo 'Once a day' &> ~/log.txt

# @hourly
0 * * * * echo 'Once an hour' &> ~/log.txt



Useful Flags


Useful Flags

coreutils exclusive flags


Useful Flags








visudo & vipw

These are two special commands to manage the super user and password files on your computer


The file that determines the timezone of the computer is located at /etc/localtime

To change what time it is, make a symbolic link from another timezone, and store it at this location.



The dns-sd diagnostic tool is useful for network scanning. If you are trying to find users to connect to via ssh, this is a great way to find out what their multicast DNS (mDNS) name is, such as tommy.local

Filesystem Hierarchy Standard

Disk Utility Functions

Encoding / Decoding Text

Binary Files