Bash Cheat Sheet¶

Beginner Concepts¶

Basic Commands¶

# Basic Commands
pwd         # Print current directory
ls          # List directory contents
cd          # Change directory
mkdir       # Make directory
touch       # Create empty file

# File Operations
cat         # Display file content
cp          # Copy files and directories
mv          # Move or rename files and directories
rm          # Remove files and directories

# Text Manipulation
echo        # Print message
grep        # Search text
sed         # Stream editor
awk         # Text processing

# Text Manipulation
echo        # Print message
grep        # Search text
sed         # Stream editor
awk         # Text processing

# Permissions
chmod       # Change file permissions
chown       # Change file ownership
chgrp       # Change group ownership

# Environment Variables
export      # Set environment variables
env         # Display environment variables

Intermediate Concepts¶

# Shell Scripting
#!/bin/bash  # Shebang line
$1, $2, ...  # Positional parameters
if ...; then
    # Code block
fi

# Conditional Statements
if ...; then
    # Code block
elif ...; then
    # Code block
else
    # Code block
fi

# Loops
for ...; do
    # Code block
done

while ...; do
    # Code block
done

# Functions
function_name() {
    # Code block
}
function_name   # Call function

# Command Substitution
variable=$(command)

# Job Control
&           # Run command in background
jobs        # List background jobs
fg          # Bring job to foreground
bg          # Resume job in background

# Redirection and Pipes
>           # Redirect output to file
>>          # Append output to file
<           # Redirect input from file
|           # Pipe output to another command

# Conditionals and Loops with Advanced Commands
find ... -exec ... \;    # Execute command for each file found
xargs ...                # Build and execute command lines from standard input

Introduction¶

Start scripts with

#!/bin/bash

Save Scripts to /bin/ directory

$ cd /bin/

Give scripts "execute" permission

$ chmod +x script.sh

To ensure that scripts in ~/bin/ are available, you must add this directory to your PATH within your configuration file

$ PATH=~/bin:$PATH

Variables¶

Within bash scripts, or the terminal, varibles are declared by setting the variable name equal to another value. So to set the variable greeting to "Hello", syntax would be,

$ greeting="Hello"

To access the value of the variable, use the name of the variable prepended with a dollar sign, ($). From previous example, to print the variable to the screen, use the following.

$ echo $greeting

Conditionals¶

Use if to start the conditional, followed by the condition in square brackets ([ ]). Leave a space between a bracket and the conditional statement! then begins the code that will run if the condition is met. else begins the code that will run if the condition is not met. Lastly, the conditional is closed with a backwards if, fi.

if [ $index -lt 5 ]
then
  echo $index
else
  echo 5
fi

Above I used -lt which is “less than”. The result of this conditional is that if $index is less than 5, it will print to the screen. If it is 5 or greater, “5” will be printed to the screen. List of comparison operators for numbers you can use within bash scripts: * Equal: -eq * Not equal: -ne * Less than or equal: -le * Less than: -lt * Greater than or equal: -ge * Greater than: -gt * Is null: -z When comparing strings, put the variable into quotes ("). This prevents errors if the variable is null or contains spaces. The common operators for comparing strings are: * Equal: == * Not equal: !=

#!/bin/bash

first_greeting="Nice to meet you!"
later_greeting="How are you?"
greeting_occasion=0 


if [ $greeting_occasion -lt 1 ]
then
    echo $first_greeting
else
    echo $later_greeting
fi

Loops¶

3 different ways to loop * for - iterate through a list and execute an action at each step * while - keep looping while the provided condition is true * until - keep looping until the condition is true

for - iterate through a list and execute an action at each step note below word is being defined at the top of the for loop so there is no $ prepended. we prepend the $ when accessing the value of the variable

for word in $paragraph
do
  echo $word
done