Bash & zsh Shell Terminal Basics Cheat Sheet

What are Bash & zsh Terminals?

Shell terminals, such as Bash and zsh, are text-based user interfaces for interacting with an operating system. They allow you to input commands through a command line, offering direct communication with the system for tasks like file manipulation, program execution, and system control. Bash is common on Linux systems and zsh is the default on MacOS systems.

Definitions

The working directory is the directory that commands are executed from. By default, commands will read and write files to this directory.

The root directory is the top of the file system. All other directories are contained within the hierarchy of this directory.

An absolute path starts from the root directory. Think of it like latitude and longitude - the values to a location don't change wherever you are.

A relative path starts from the working directory. Think of it like directions from where you are, like "20 kilometers West from here".

A glob pattern is a way of specifying multiple files at once.

A regular expression is a more complex way of specifying text fragments. Learn more in DataCamp's Regular Expressions Cheat Sheet.

Getting Help

Display the manual for a command with man

man head

File System Navigation

Print the current working directory with pwd

pwd

Change the current working directory with cd

cd data/raw # Go to raw dir inside data dir inside current dir

Absolute paths start with the root directory, /

cd /home 

Relative paths can start with the current working directory, .

cd ./images

Move up to the parent directory with .. (can be used repeatedly)

cd ../.. # Go to grandparent directory

List files and folders in the current working directory with ls

ls

List all files and folders, including hidden ones (names starting .) with ls -a

ls -a

List files and folders in a human-readable format with ls -lh

ls -lh

List files and folders matching a glob pattern with ls pattern

ls *.csv # Returns all CSV files

Recursively list all files below the current working directory with ls -R

ls -R

List estimated disk usage of files and folders in a human-readable format with du -ah

du -ah

Find files by name in the current directory & its subdirectories with find . -type f -name pattern

find . -type f -name *.ipynb # Find Juypter notebooks

Displaying Files

Display the whole file with cat

cat README.txt

Display a whole file, a page at a time with less

less README.txt

Display the first few lines of a file with head

head -n 10 filename sales.csv # Get first 10 lines of sales.csv

Display the last few lines of a file with tail

tail -n 10 filename sales.csv # Get last 10 lines of sales.csv

Display columns of a CSV file with cut

cut -d , -f 2-5, 8 sales.csv # Using comma delimiter, select fields 2 to 5 & 8

Display the lines of a file containing text matching a regular expression with grep

grep [0-9]+ sales.csv # Matches lines containing numbers

Display the names of files with filenames containing text matching a regular expression with grep -r

grep -r sales[0-9]+\.csv # Matches filesnames with "sales", numbers, dot "csv"

Get the line word & character count of a file with wc

wc README.txt

Copying, Moving and Removing Files

Copy (and paste) a file to a new directory with cp

cp sales.csv data/sales-2023.csv # Copy to data dir and rename

Copy files matching a glob pattern with cp pattern newdir

cp *.csv data/ # Copy all CSV files to data dir

Move (cut and paste) a file to a new directory with mv

mv sales.csv data/sales-2023.csv # Move to data dir and rename

Rename a file by moving it into the current directory

mv sales.csv sales-2023.csv 

Move files matching a glob pattern with mv pattern newdir

mv *.csv data/ # Move all CSV files to data dir

Prevent overwriting existing files with mv -n

mv -n sales.csv data/sales-2023.csv # Rename unless new filename exists

Remove (delete) a file with rm

rm bad_data.json

Remove a directory with rmdir

rmdir temp_results

Combining commands

Redirect the output from a command to a file with >

head -n 5 sales.csv > top_sales.csv

Pipe the output from a command to another command with |

head -n 5 sales.csv | tail -n 1

Redirect the input to a command with <

head -n 5 < sales.csv

Glob Patterns

Match one or more character with *

*.txt # Match all txt files

Match a single character with ?

sales202?.csv # Match this decade's sales data files

Match any character in the square brackets with [...]

sales202[0123].csv # Match sales data files for 2020 to 2023

Match any patterns listed in the curly braces with {...}

{*.csv *.tsv} # Matches all CSV and TSV files

Manipulating File Contents

Sort lines of a file with sort

sort random_order.txt

Sort in descending order using sort -r

sort -r random_order.txt

Combine cut and sort using a pipe to sort a column of a CSV file

cut -d , -f 2 | sort

Remove adjacent duplicate lines with uniq

uniq sales.csv

Get counts of (adjacent) duplicate lines with uniq -c

uniq -c sales.csv

Combine sort and uniq using a pipe to remove duplicate lines

sort random_order.txt | uniq

Variables

List all environment variables with set

set

Create a shell variable with name=value (no spaces around =)

mydata=sales.csv

Create a shell variable from the output of a command with name=$(command)

pyfiles=$(ls *.py)

Print an environment variable or shell variable name with echo $value

echo $HOME

Convert a shell variable into an environment variable with export

export mydata

Loops and Flow Control

Execute a command for multiple values with for variable in values; do command; done

datafiles=*.csv
for file in datafiles; do echo $file; done

Spread loops over multiple lines for increased readability

datafiles=*.csv
for file in datafiles
do 
    echo $file
done

Conditionally execute code with if [ condn ]; then command; else alt_command; fi

x=99;
if [ $x > 50 ] ; then
    echo "too high";
elif [ $x < 50 ] ; then
    echo "too low";
else
    echo "spot on";
fi

Reusing Commands

See your previous commands with history

history

Save commands in a shell file (extension .sh) and run them with bash or zsh

bash mycommands.sh 
zsh mycommands.sh