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Core Commands

Here I list core commands (e.g. ps, du, find) grouped by functionality for proficient use of the shell.

pwd Print Working Dir​

pwd prints the absolute filepath of the current working directory.

pwd

Will print out something like:

/home/users/Documents

du Disk Usage​

One mistake I used to make is use ls -lah to see directory sizes, which always surprisingly small, until I realized it only displayed the size of the directory entry, not its contents. To see actual disk usage of an entire directory, use du -sh where -s summarizes and -h makes the size human readable. Note that du without any arguments will evaluate the current . directory. The du command displays both directory and file sizes.

Detail

By default, the du command will evaluate the disk usage of the argument directory and evaluate all of its subdirectories and files. If you do not want to see all the subdirectories and files, the -s flag displays only the sum total disk usage of the argument directory or file.

# Show size of each subdirectory in current directory
du -sh *

# Show size of a specific directory (and its subdirectories)
du -sh path/to/dir

# Show a sorted list of the biggest directories/files
du -sh * | sort -h

df Disk Free​

While du tells you the size of files and directories, the df command stands for "disk free" and reports the amount of available and used disk space on mounted filesystems.

df -h # get human readable file system

An example output looks like this:

Filesystem      Size  Used Avail Use% Mounted on
none            3.9G     0  3.9G   0% /usr/lib/modules/6.6.87.2-microsoft-standard-WSL2
none            3.9G  4.0K  3.9G   1% /mnt/wslg/
C:\             476G  399G   77G  84% /mnt/c

Another common use case is checking the shared memory:

df -h /dev/shm

find Find Files​

Often find is used to specifically look for files or directories. The command find can be used to search for a file by filename if you're not sure where you saved it:

find / -name "somefile.txt" 2>/dev/null
# /home/dave/Documents/somefile.txt

For partial search use asterisks in the name, also use iname for case insensitive:

find / -iname "*foo*.txt" 2>/dev/null
# can match the following:
# /home/dave/Documents/foobar.txt
# /home/dave/Documents/Foo.txt
name vs. iname

The name option matches filename by shell pattern (do not give it slashes as it only matches filename). The key difference with the counterpart iname is that iname makes the match case insensitive. The asterisk * works the same in both cases.

Trick

Use 2>/dev/null to silence permission errors - redirecting stderr. File descriptors 0 is stdin, 1 is **stdout, and 2 is stderr. So 2> redirects stderr to /dev/null which is essentially a special device that discards everything (think of it as a black hole). Writing to it just throws it away.

List contents of a directory with the -ls option:

find ~/Documents -ls

Find files by type: use -type f for regular file, -type d for directory.

find ~ -type f

This allows you to list directories in a filepath (which ls cannot do). You might want to limit the depth (because it is recursive) using the -maxdepth option:

find ~/Public/ -type d -maxdepth 1
# there is also a -mindepth N option!

You'll often do this in your current directory:

  • find . -type f - find current directory files
  • find . -type d - find current directory subdirectories
  • find . -type l - find current directory symlinks

Other common patterns with find involve filtering by sizes:

  • find . -size +100M - find files bigger than 100MB
  • find . -size -10k - find files smaller than 10KB

Or filtering by owners:

  • find . -user dave
  • find . -group staff
  • find . -perm 644

Combine conditions with AND (-and), OR (-o), Negation (!):

# OR
find . -type f -name "*.log" -o -name "*.txt"
# AND
find . -type f -name "*.sh" -and -executable
# NEGATE
find . -type f ! -name "*.txt"

You can also perform actions on results via -delete and -exec for executing a command:

find . -name "*.txt" -exec rm {} +

As an example of how I used find, recently my error output identified some directory with problematic files. Since it did not print the exact filepath, I just used find to locate it:

find data/imagery -type d -name "20160311_464_837"

tree Directory Listing​

Pitfall

tree is not a built-in command on bash, so you will need to do sudo apt install tree.

The command recursively lists contents of directories in depth-indented, tree like format, providing visual representation of directory structure.

Flags:

  • -d - list directories only
  • -L - limit depth so -L 2 to limit 2 levels deep

Example:

tree

Gets you the following output (in your current working directory):

.
├── 01-core-commands.mdx
├── 02-shortcuts.mdx
├── 03-cli-tools.mdx
└── 04-scripting.mdx

0 directories, 4 files

File Management​

cp, mv, rm, touch​

chmod​

chown​

ln​

Inspection​

cat​

less​

tail​

file​

stat​

which​

Text Processing​

grep​

awk​

sed​

cut​

sort​

uniq​

wc​

Networking​

curl​

wget​

ping​

netstat​

ssh​

scp​

System Monitoring​

ps​

top​

htop​

kill​

uptime​

free​

Execution​

source​

exec​

To restart the shell e.g. if you have just installed conda, use exec:

exec $SHELL

This replaces the current shell with a brand new instance. You can also get a similar effect by reloading configurations and refreshing settings using source ~/.bashrc.