Shell Scripting Reference

https://speedsheet.io/s/bash
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### For Loop Initialization

Source: https://speedsheet.io/s/bash?q=control-only

Examples of different ways to initialize or define the range for a 'for' loop.

```bash
for ((value=0; value < max; value++))
```

```bash
for value in {first..last}
```

```bash
for value in "${array_1[@]}"
```

```bash
for value in "value 1" "value 2" "value 3"
```

--------------------------------

### Rsync with Identity File

Source: https://speedsheet.io/s/bash

Example of using rsync with a specified identity file for authentication.

```bash
rsync -i identity_file_path ...
```

--------------------------------

### Get CPU Details

Source: https://speedsheet.io/s/bash

Lists detailed information about the system's CPU. Requires the 'util-linux' package.

```bash
lscpu
```

--------------------------------

### Get PCI Device Details

Source: https://speedsheet.io/s/bash

Lists detailed information about the system's PCI devices. This command is part of the 'pciutils' package and may not be installed by default.

```bash
lspci
```

--------------------------------

### Example of Resetting Color

Source: https://speedsheet.io/s/bash

Shows how to apply a specific foreground color and then reset it using the defined escape sequence.

```bash
echo "\e[93m Green \e[0m Reset"
```

--------------------------------

### Get Host Name

Source: https://speedsheet.io/s/bash

Displays the system's network host name.

```bash
hostname
```

```bash
hostnamectl
```

--------------------------------

### Get Operating System Name

Source: https://speedsheet.io/s/bash

Returns the name of the Operating System.

```bash
uname
```

--------------------------------

### Get Bash Version

Source: https://speedsheet.io/s/bash

Retrieves the installed Bash version information.

```bash
bash --version
```

```bash
echo $BASH_VERSION
```

```bash
echo ${BASH_VERSION%%[^0-9.]*}
```

--------------------------------

### Set Prompt to Host Name and Current Path

Source: https://speedsheet.io/s/bash

Combines the hostname and the full current path in the prompt, separated by a colon. Example output: host-1:~/downloads>

```bash
PS1="\h:\w>"
```

--------------------------------

### Start a New Bash Shell

Source: https://speedsheet.io/s/bash

Initiates a new interactive Bash shell session.

```bash
/usr/bin/env bash
```

```bash
/bin/bash
```

--------------------------------

### Document Comment Example

Source: https://speedsheet.io/s/bash?q=fundamentals-only

Place documentation comments before functions to provide context. Use a single hash '#' before the descriptive text.

```bash
# This is a doc comment. function_1() { ... }
```

```bash
# This is a doc comment. # Adds context to the # following function. function_1() { ... }
```

--------------------------------

### Example of Resetting Background Color

Source: https://speedsheet.io/s/bash

Illustrates applying a specific background color and then resetting it to the default using the escape sequence.

```bash
echo "\e[104m Light Blue Background \e[49m Reset"
```

--------------------------------

### Get Running Shell

Source: https://speedsheet.io/s/bash

Identifies the currently active shell process. Example results include 'bash' or '-zsh'.

```bash
ps -ocomm= $$
```

--------------------------------

### Example Usage of ANSI Colors

Source: https://speedsheet.io/s/bash

Demonstrates how to use predefined ANSI color variables to print text with specific foreground and background colors, followed by a reset.

```bash
echo "${LIGHT_GREEN}${ON_DARK_GRAY} Prints Light Green on Dark Gray ${RESET_COLOR}"
```

--------------------------------

### Example Usage of Variable

Source: https://speedsheet.io/s/bash?q=variables-only

Demonstrates how to use a variable within an echo command, ensuring proper quoting for values with spaces.

```bash
text="Print this text."
echo "$text"
```

--------------------------------

### Get Operating System Details

Source: https://speedsheet.io/s/bash

Provides detailed information about the OS version. Multiple commands can be used to retrieve this information.

```bash
hostnamectl
```

```bash
cat /etc/os-release
```

```bash
cat /etc/*-release
```

```bash
cat /proc/version
```

--------------------------------

### Find Lines Starting With a String

Source: https://speedsheet.io/s/bash?q=files-only

Use the `look` command to retrieve lines from a file that begin with a specified prefix.

```bash
look starting_with file_1
```

```bash
look starting_with files
```

--------------------------------

### Full Named Pipe Example

Source: https://speedsheet.io/s/bash

Demonstrates a complete inter-process communication scenario using named pipes. Terminal 1 creates the pipe and listens for input, while Terminal 2 sends data to it.

```bash
mkfifo pipe-1
cat < pipe-1
```

```bash
cat > pipe-1
Send this over the pipe. CTRL + D
```

```bash
rm pipe-1
```

--------------------------------

### Get File Information

Source: https://speedsheet.io/s/bash?q=files-only

Use the `file` command to determine the type and properties of a file, such as executable status, text content, and encoding.

```bash
file file_name
```

--------------------------------

### Get System IO Information

Source: https://speedsheet.io/s/bash

Displays I/O statistics and CPU usage over a specified length of time and count.

```bash
iostat length count
```

--------------------------------

### Get First 10 Lines of String

Source: https://speedsheet.io/s/bash

Returns the first 10 lines of a string using the `head` command. Pipe the string output to `head`.

```bash
command | head
```

--------------------------------

### Show Command Help

Source: https://speedsheet.io/s/bash

Displays the manual page for a given command, providing detailed usage information. Press 'Q' to exit.

```bash
man command
```

--------------------------------

### Slice a Bash array to get a subarray

Source: https://speedsheet.io/s/bash?q=array-only

Extracts a portion of an array defined by a starting index and a length.

```bash
array_1=(1 2 3 4 5 6)
array_2=("${array_1[@]:2:3}")
# array_2 will contain (3 4 5)
```

--------------------------------

### Get System Information

Source: https://speedsheet.io/s/bash

Displays system information, including free memory and CPU usage, over a specified length of time and count.

```bash
vmstat length count
```

--------------------------------

### Get all elements except the first from a Bash array

Source: https://speedsheet.io/s/bash?q=array-only

Returns a subarray containing all elements starting from the second element (index 1) to the end.

```bash
array_1=("one" "two" "three")
remainder=("${array_1[@]:1}")
echo "${remainder[@]}"
```

--------------------------------

### Create Directory

Source: https://speedsheet.io/s/bash?q=files-only

Creates a new directory with the specified name.

```bash
mkdir directory
```

--------------------------------

### View First 10 Lines of a File

Source: https://speedsheet.io/s/bash?q=files-only

Use `head` to display the initial 10 lines of a specified file.

```bash
head file_name
```

--------------------------------

### Basic 'Hello World' Script

Source: https://speedsheet.io/s/bash

A simple Bash script to print 'Hello world!' to the console. This is the most basic script to verify Bash execution.

```bash
echo "Hello world!"
```

--------------------------------

### Slice Bash Array from Start

Source: https://speedsheet.io/s/bash

Extracts a portion of a bash array starting from a specified index to the end.

```bash
array_1=(1 2 3 4 5 6)
array_2=("${array_1[@]:4}")
```

--------------------------------

### Create Directory with Subdirectories

Source: https://speedsheet.io/s/bash?q=files-only

Creates a directory and any necessary parent directories that do not already exist.

```bash
mkdir -p directory/directory/directory
```

--------------------------------

### Bash Case Statement Execution Example

Source: https://speedsheet.io/s/bash?q=case-only

An example of a Bash case statement that executes commands based on a variable's value.

```bash
command="start"
case "$command":
  "start") echo "Starting" ;; 
  "stop") echo "Stopping" ;; 
esac
```

--------------------------------

### Extract Substring Using Bash Parameter Expansion

Source: https://speedsheet.io/s/bash

Extracts a portion of a string based on a starting position and length. The start position is 0-indexed.

```bash
=${string_1:start:length}
```

```bash
string_1="012345" substring=${string_1:2:2} echo "$substring"
```

--------------------------------

### Mirror Directory with rsync

Source: https://speedsheet.io/s/bash?q=files-only

Mirrors the contents of a source directory to a target directory using rsync, ensuring both directories are identical. Requires rsync to be installed.

```bash
rsync -avE --delete source_directory/ target_parent_directory/
```

--------------------------------

### Get All Values Separated by IFS in Bash

Source: https://speedsheet.io/s/bash?q=associative-array-only

Use "${dict_1[*]}" to get values as a single word, separated by the first character of IFS.

```bash
="${dict_1[*]}"
```

--------------------------------

### List All Processes

Source: https://speedsheet.io/s/bash?q=processes-only

Use the `ps` command to display information about running processes. Options like `-e` (every process) and `-f` (full format) provide detailed output.

```bash
ps
```

```bash
ps -ef
```

```bash
ps -o ruser,pid,vsz,s,uid,comm -p id
```

```bash
ps -e -o ruser,pid,s,vsz,stime,time,comm
```

--------------------------------

### Get All Keys Separated by IFS in Bash

Source: https://speedsheet.io/s/bash?q=associative-array-only

Use "${!dict_1[*]}" to get keys as a single word, separated by the first character of IFS.

```bash
="${!dict_1[*]}"
```

--------------------------------

### Run Command or Fallback

Source: https://speedsheet.io/s/bash

Use '&&' for success and '||' for fallback to execute a command, and if it fails, execute an alternative.

```bash
command_1 && successful_command || fallback_command
```

--------------------------------

### Get Drive Size and Free Space

Source: https://speedsheet.io/s/bash

Displays disk usage information for specified drive paths, showing size and available space in a human-readable format.

```bash
df -h drive_path
```

```bash
df -k drive_path
```

```bash
df -g drive_path
```

--------------------------------

### Get Current User

Source: https://speedsheet.io/s/bash

Displays the username of the currently logged-in user.

```bash
=$USER
```

```bash
logname
```

--------------------------------

### 'Hello World' Script with User Input

Source: https://speedsheet.io/s/bash

This Bash script prompts the user for their name and then prints a personalized greeting. It uses `read -p` to display a prompt and capture user input.

```bash
#!/usr/bin/env bash
read -p "Name: " name
echo "Hello $name!"
```

--------------------------------

### Get Current User Information

Source: https://speedsheet.io/s/bash?q=user-only

Displays comprehensive information about the current user, including their ID, name, and associated groups.

```bash
id
```

--------------------------------

### 'Hello World' Script with Argument or Input

Source: https://speedsheet.io/s/bash

An advanced Bash script that greets a user. It prioritizes a name provided as a command-line argument; otherwise, it prompts the user for input. This script demonstrates basic function usage in Bash.

```bash
#!/usr/bin/env bash

get_name() {
  # stores the input into the variable '`name`':
  read -p "Name: " name
}

print_hello() {
  local name="$@"
  echo "Hello $name!"
}

if [[ -z "$1" ]]; then
  get_name
else
  name="$@"
fi

print_hello "$name"
```

--------------------------------

### Get Current Process ID

Source: https://speedsheet.io/s/bash

Returns the process ID of the current shell.

```bash
$$
```

```bash
echo $$
```

--------------------------------

### Create a File from Command-line Input

Source: https://speedsheet.io/s/bash?q=files-only

Create a file by typing content directly into the terminal after the `cat > file_name` command, ending with Ctrl+D.

```bash
cat > file_name ...content... Ctrl + D
```

--------------------------------

### List Top Processes by CPU Usage

Source: https://speedsheet.io/s/bash?q=processes-only

Use `top` to view a dynamic, real-time list of processes, sorted by CPU usage by default. The output includes PID, CPU%, Memory, and command.

```bash
top
```

```bash
ps -eo pid,%cpu,%mem,vsize,start,args | sort -k 2 -nr | head -25
```

--------------------------------

### List Top 25 Processes by Memory Size

Source: https://speedsheet.io/s/bash

Shows the top 25 processes sorted by memory size. Displays Process ID, CPU %, Memory, Virtual Memory Size, Start Date, and Command-line.

```bash
ps -eo pid,%cpu,%mem,vsize,start,args | sort -k 4 -nr | head -25
```

--------------------------------

### Get Operating System Kernel Version

Source: https://speedsheet.io/s/bash

Retrieves the kernel version of the operating system.

```bash
uname -r
```

--------------------------------

### Get Current User ID

Source: https://speedsheet.io/s/bash?q=user-only

Displays the unique numerical identifier for the current user.

```bash
id -u
```

--------------------------------

### List Top 25 Processes by CPU Usage

Source: https://speedsheet.io/s/bash

Shows the top 25 processes sorted by CPU usage. Displays Process ID, CPU %, Memory, Virtual Memory Size, Start Date, and Command-line.

```bash
ps -eo pid,%cpu,%mem,vsize,start,args | sort -k 2 -nr | head -25
```

--------------------------------

### List All Users on System

Source: https://speedsheet.io/s/bash

Displays all user accounts on the system by reading the '/etc/passwd' file.

```bash
cat /etc/passwd
```

--------------------------------

### Get the size of a Bash array

Source: https://speedsheet.io/s/bash?q=array-only

Returns the number of elements currently stored in an array.

```bash
array_1=("one" "two" "three")
echo "${#array_1[@]}"
```

--------------------------------

### Get CPU Type

Source: https://speedsheet.io/s/bash

Returns the machine hardware name, indicating the CPU type. Useful for identifying specific hardware like M1 Macs.

```bash
uname -m
```

```bash
if [[ $(uname -m) == 'arm64' ]]; then echo "M1 Mac" fi
```

--------------------------------

### Get First N Lines of String

Source: https://speedsheet.io/s/bash

Returns the first `count` lines of a string. Specify the number of lines using the `-n` option with `head`.

```bash
command | head -n count
```

--------------------------------

### List Mounted Devices

Source: https://speedsheet.io/s/bash

Displays all currently mounted file systems and their mount points.

```bash
mount
```

--------------------------------

### Get the first item from a Bash array

Source: https://speedsheet.io/s/bash?q=array-only

Retrieves the element at index 0 from an array.

```bash
array_1=("one" "two" "three")
echo "${array_1[0]}"
```

--------------------------------

### Get Total System Memory

Source: https://speedsheet.io/s/bash

Extracts the total system memory in kilobytes from the `/proc/meminfo` file.

```bash
grep MemTotal /proc/meminfo | awk '{print $2}'
```

--------------------------------

### Navigate to Parent Directory

Source: https://speedsheet.io/s/bash?q=symbols-only

The '..' symbol represents the parent directory.

```bash
cd ..
```

--------------------------------

### Get Parameter Count

Source: https://speedsheet.io/s/bash?q=parameters-only

Returns the total number of command-line arguments passed to the script or function.

```bash
$#
```

--------------------------------

### List Top Processes by CPU Usage

Source: https://speedsheet.io/s/bash

Lists the top applications by CPU usage.

```bash
top
```

--------------------------------

### Navigate to Home Directory

Source: https://speedsheet.io/s/bash?q=symbols-only

The '~' symbol represents the user's home directory.

```bash
cd ~
```

--------------------------------

### Get Command/Script Name

Source: https://speedsheet.io/s/bash?q=parameters-only

Retrieves the name of the script or command that was executed, including any path used.

```bash
$0
```

--------------------------------

### Get Local IP Address

Source: https://speedsheet.io/s/bash

Lists the server's local IP address. Multiple commands are provided as compatibility may vary across systems.

```bash
hostname -I
```

```bash
ip addr show
```

```bash
sudo /sbin/ifconfig -a
```

```bash
ifconfig | sed -En 's/127.0.0.1//;s/.*inet (addr:)?(([0-9]*.){3}[0-9]*).*/2/p'
```

--------------------------------

### Set Prompt to Host Name

Source: https://speedsheet.io/s/bash

Sets the prompt to display the full hostname of the server.

```bash
PS1=\H
```

--------------------------------

### Get an item from a Bash array by position

Source: https://speedsheet.io/s/bash?q=array-only

Retrieves the element at a specific zero-based index from an array.

```bash
array_1=("one" "two" "three")
echo "${array_1[1]}"
```

--------------------------------

### Access Individual Parameters

Source: https://speedsheet.io/s/bash?q=parameters-only

References positional parameters passed to the script, starting from $1 for the first parameter.

```bash
$1 $2 $3 ...
```

--------------------------------

### Get Script Run Command

Source: https://speedsheet.io/s/bash

Retrieves the command used to execute the script, including the path if it was specified.

```bash
=$0
```

--------------------------------

### Run Command or Fallback Command

Source: https://speedsheet.io/s/bash?q=command-execution-only

Use '&&' and '||' to execute a fallback command if the initial command fails.

```bash
command_1 && successful_command || fallback_command

```

--------------------------------

### Get String Length

Source: https://speedsheet.io/s/bash

Returns the length of a string using the `${#string_name}` syntax. This is a Bash parameter expansion.

```bash
string_1="12345" length="${#string_1}" # Returns 5
```

--------------------------------

### View First N Lines of a File

Source: https://speedsheet.io/s/bash?q=files-only

Use `head -n` to display a specific number of lines from the beginning of a file.

```bash
head -n count file_name
```

--------------------------------

### Show Directory Sizes

Source: https://speedsheet.io/s/bash?q=files-only

Displays the sizes of directories. Use the -h option for human-readable output, -k for kilobytes, or -ks to list sizes for each file. The output can be sorted and piped to head for summary information.

```bash
du
```

```bash
du -h directory_path
```

```bash
du -k | sort -rn | head
```

--------------------------------

### Get the last item from a Bash array

Source: https://speedsheet.io/s/bash?q=array-only

Retrieves the last element from an array using negative indexing.

```bash
array_1=("one" "two" "three")
echo "${array_1[-1]}"
```

--------------------------------

### Create a User Group

Source: https://speedsheet.io/s/bash

Adds a new user group to the system.

```bash
groupadd group_name
```

--------------------------------

### Navigate to Current Directory

Source: https://speedsheet.io/s/bash?q=symbols-only

The '.' symbol represents the current directory.

```bash
cd .
```

--------------------------------

### Set Terminal Backspace Key

Source: https://speedsheet.io/s/bash

Configures the terminal's backspace key behavior. For example, setting it to Ctrl+H.

```bash
stty erase backspace_key
```

```bash
stty erase ^H
```

--------------------------------

### Show System Uptime

Source: https://speedsheet.io/s/bash

Displays how long the system has been running since the last boot.

```bash
uptime
```

--------------------------------

### List Block Level Devices

Source: https://speedsheet.io/s/bash

Shows all storage devices recognized at the block level by the system.

```bash
lsblk
```

--------------------------------

### List All Drives and Free Space

Source: https://speedsheet.io/s/bash

Shows disk usage for all mounted drives, including size and available space in a human-readable format.

```bash
df -h
```

```bash
df -k
```

```bash
df -g
```

--------------------------------

### Get Full File Path

Source: https://speedsheet.io/s/bash?q=files-only

Use the `realpath` command to resolve a file name to its absolute, canonical path.

```bash
realpath file_name
```

--------------------------------

### Display User Home Directory

Source: https://speedsheet.io/s/bash

Prints the current user's home directory path. Ensure the HOME environment variable is set.

```bash
echo "$HOME"
```

--------------------------------

### Get Array Elements (Separate Words)

Source: https://speedsheet.io/s/bash?q=symbols-only

The '[@]' symbol returns all elements from an array or associative array as separate words.

```bash
=items_1[@]
```

--------------------------------

### Get Variable Value

Source: https://speedsheet.io/s/bash?q=variables-only

Retrieves the value of a variable. Use double quotes to handle values containing spaces.

```bash
=$variable_1
="$variable_1"
="${variable_1}"
```

--------------------------------

### Get Current User Name

Source: https://speedsheet.io/s/bash?q=user-only

Shows the login name of the current user. Both 'whoami' and 'logname' commands achieve this.

```bash
whoami
```

```bash
logname
```

--------------------------------

### Create an Empty File

Source: https://speedsheet.io/s/bash?q=files-only

Create an empty file using either `echo -n "" > file_name` or the `touch file_name` command.

```bash
echo -n "" > file_name
```

```bash
touch file_name
```

--------------------------------

### Get All Values from Bash Associative Array

Source: https://speedsheet.io/s/bash?q=associative-array-only

Use "${dict_1[@]}" to retrieve all values from the associative array.

```bash
="${dict_1[@]}"
```

--------------------------------

### Check if String Starts With Prefix in Bash

Source: https://speedsheet.io/s/bash?q=operators-only

Use the == operator with a wildcard to verify if a string begins with a specified prefix.

```bash
"$string_1" == "$start"*
if [[ $string_1 == "$start"* ]] ; then ... fi
```

--------------------------------

### Create Symbolic Link

Source: https://speedsheet.io/s/bash?q=files-only

Creates a symbolic link to a source file or directory. The -s option allows linking across different devices.

```bash
ln -s source_path link_name
```

--------------------------------

### Access Parameters Excluding First

Source: https://speedsheet.io/s/bash?q=parameters-only

References all parameters starting from the second one. Parameters are individually quoted, preserving spaces.

```bash
${@:2}
```

--------------------------------

### Compare Two Files

Source: https://speedsheet.io/s/bash?q=files-only

Use the `diff` command to show line-by-line differences between two files.

```bash
diff file_1 file_2
```

--------------------------------

### Bash Case Statement - Basic Example

Source: https://speedsheet.io/s/bash?q=control-only

Executes a clause based on the value of a variable. 'case' is case-sensitive, and ';;' terminates each clause.

```bash
command="start"
case "$command":
  "start") echo "Starting" ;;
  "stop") echo "Stopping" ;;
esac
```

--------------------------------

### Connect to SFTP Server

Source: https://speedsheet.io/s/bash

Connects to an SFTP server. Supports connecting with a PEM file for authentication.

```bash
sftp user_id@server.com
```

```bash
sftp -i server_pem_file user_id@server.com
```

--------------------------------

### Copy a File

Source: https://speedsheet.io/s/bash?q=files-only

Use the `cp` command to copy a file. Options `-a` preserves attributes, and `-v` enables verbose output.

```bash
cp source_file new_file
```

--------------------------------

### Get Operating System Type from Variable

Source: https://speedsheet.io/s/bash

Returns the CPU type from the OSTYPE variable. Useful for OS-specific conditional logic.

```bash
$OSTYPE
```

```bash
if [[ $OSTYPE == 'darwin'* ]]; then ... fi
```

--------------------------------

### Get Public IP Address

Source: https://speedsheet.io/s/bash

Retrieves the public-facing IP address of the server using an external IP information service.

```bash
curl -s "ipinfo.io" | grep -Eo '"ip":.*?[^\\]*,' | sed 's/^.*: "//;s/",//'
```

--------------------------------

### Basic String Literals

Source: https://speedsheet.io/s/bash

Demonstrates the basic syntax for string literals in Bash, including unquoted, single-quoted, and double-quoted strings.

```bash
string
'a string'
"a string"
```

--------------------------------

### Get Public Host Name

Source: https://speedsheet.io/s/bash

Retrieves the public host name of the server using an external IP information service.

```bash
curl -s "ipinfo.io" | grep -Eo '"hostname":.*?[^\\]*,' | sed 's/^.*: "//;s/",//'
```

--------------------------------

### Create Symbolic Link (Copy)

Source: https://speedsheet.io/s/bash?q=files-only

Creates a symbolic link to a source file or directory. Using the -p option preserves the link itself, rather than copying the target's content.

```bash
cp -P source_link new_link
```

--------------------------------

### List Local Network Devices

Source: https://speedsheet.io/s/bash

Lists all local devices connected to the network, showing their IP addresses.

```bash
arp -a
```

--------------------------------

### Get CPU Architecture

Source: https://speedsheet.io/s/bash

Retrieves the CPU architecture type. Useful for conditional logic based on the system's processor.

```bash
uname -p
```

```bash
if [[ $(uname -p) == 'arm' ]]; then echo "Arm Based System" fi
```

--------------------------------

### Download File with Wget

Source: https://speedsheet.io/s/bash

Downloads a web page or file using wget. Use '-O' to specify the output filename and '-q' for quiet mode.

```bash
wget http://site.com/page
```

```bash
wget -O file_name http://site.com/page
```

--------------------------------

### Get all elements except the last from a Bash array

Source: https://speedsheet.io/s/bash?q=array-only

Returns a subarray containing all elements from the beginning up to, but not including, the last element.

```bash
array_1=("one" "two" "three")
subarray=("${array_1[@]:0:${#array_1[@]}-1}")
echo "${subarray[@]}"
```

--------------------------------

### View File Contents Paged

Source: https://speedsheet.io/s/bash?q=files-only

Use the `more` command to view file content one screen at a time. Supports basic navigation keys.

```bash
more file_name
```

--------------------------------

### Get all elements from a Bash array

Source: https://speedsheet.io/s/bash?q=array-only

Retrieves all elements of an array, typically used when passing the array to another command or variable.

```bash
array_1=("one" "two" "three")
all=("${array_1[@]}")
echo "${all[@]}"
```

--------------------------------

### Set Prompt to Bash Version

Source: https://speedsheet.io/s/bash

Sets the prompt to display the current Bash version.

```bash
PS1=\v
```

--------------------------------

### Get All Keys from Bash Associative Array

Source: https://speedsheet.io/s/bash?q=associative-array-only

Use "${!dict_1[@]}" to retrieve all keys. The order of keys is not guaranteed.

```bash
="${!dict_1[@]}"
```

--------------------------------

### List All User Groups (Linux)

Source: https://speedsheet.io/s/bash

Displays all user groups on the system by reading the /etc/group file.

```bash
cat /etc/group
```

```bash
cut -d: -f1 /etc/group | sort
```

--------------------------------

### Extract Substring from Start in Bash

Source: https://speedsheet.io/s/bash

Extracts a substring from the beginning of a string up to a specified length. This is a specific case of general substring extraction.

```bash
=${string_1:0:length}
```

```bash
string_1="012345" substring=${string_1:0:2} echo "$substring"
```

--------------------------------

### Bash Case Statement Basics

Source: https://speedsheet.io/s/bash?q=case-only

Demonstrates the basic structure of a Bash case statement with multiple value clauses.

```bash
case "$string_1" in value_1) ... ;; value_2) ... ;; value_3 | value_4 | value_5) ... ;; *) # Default: ... ;; esac
```

--------------------------------

### Single-Line Comment in Bash

Source: https://speedsheet.io/s/bash?q=fundamentals-only

Use the hash symbol '#' to start a comment line in Bash. Any text following '#' on the same line is ignored by the interpreter.

```bash
# Comments - Single Line
```

--------------------------------

### Find Processes with Full Command-line

Source: https://speedsheet.io/s/bash?q=processes-only

Display the full command-line of matching processes using pgrep. This is useful when the process name alone is insufficient.

```bash
pgrep -fl ...
```

```bash
pgrep -a ...
```

--------------------------------

### Change File Permissions Only

Source: https://speedsheet.io/s/bash?q=files-only

Use `find` with `chmod` to selectively change permissions for files. This example sets file permissions to 644.

```bash
find path -type f -exec chmod 644 {} +
```

```bash
chmod 644 $(find path -type f)
```

--------------------------------

### Change Directory Permissions Only

Source: https://speedsheet.io/s/bash?q=files-only

Use `find` with `chmod` to selectively change permissions for directories. This example sets directory permissions to 755.

```bash
find path -type d -exec chmod 755 {} +
```

```bash
chmod 755 $(find path -type d)
```

--------------------------------

### Set Prompt to Host Name Up To '.'

Source: https://speedsheet.io/s/bash

Sets the prompt to display the hostname truncated at the first period ('.').

```bash
PS1=\h
```

--------------------------------

### Create a New User

Source: https://speedsheet.io/s/bash?q=user-only

Creates a new user account. Use the -g option to add the user to a specific group.

```bash
adduser user_name
```

```bash
adduser -g group_name user_name
```

--------------------------------

### Get All Values from Associative Array

Source: https://speedsheet.io/s/bash

Retrieve all values from an associative array using the `array[@]` syntax. Each value is treated as a separate element.

```bash
echo "${dict_1[@]}"
```

--------------------------------

### Trace Route to Server

Source: https://speedsheet.io/s/bash

Traces the route to a server, mapping each hop along the way and displaying the journey time.

```bash
traceroute ip_address
```

```bash
traceroute url
```

--------------------------------

### List All Drives

Source: https://speedsheet.io/s/bash

Displays a list of all drives connected to the system. Note: Functionality may vary across Linux versions.

```bash
diskutil list
```

--------------------------------

### Extract Directory from File Path

Source: https://speedsheet.io/s/bash?q=files-only

Use `dirname` to get the directory component of a given file path. Returns '.' if no directory is present.

```bash
dirname $file_path
```

```bash
directory="$(dirname "$file_path")"
```

--------------------------------

### Switch to Root User

Source: https://speedsheet.io/s/bash

Switches the current user identity to the root user. Use 'su' without any options to become root.

```bash
su
```

--------------------------------

### Get Return Code

Source: https://speedsheet.io/s/bash?q=parameters-only

Retrieves the exit status of the last executed command or script. A value of 0 typically indicates success.

```bash
$?
```

--------------------------------

### Show Current Directory Path

Source: https://speedsheet.io/s/bash?q=files-only

Prints the full path of the current working directory.

```bash
pwd
```

--------------------------------

### Get Specific Value from Bash Associative Array

Source: https://speedsheet.io/s/bash?q=associative-array-only

Access a value by its key using the syntax "${dict_1[name]}".

```bash
="${dict_1[name]}"
```

--------------------------------

### View File Contents

Source: https://speedsheet.io/s/bash?q=files-only

Use the `cat` command to display the entire content of a file to standard output.

```bash
cat file_name
```

--------------------------------

### Extract Substring from End in Bash

Source: https://speedsheet.io/s/bash

Extracts the remainder of a string starting from a specified position. A negative length with a preceding space extracts from the end.

```bash
=${string_1:start}
```

```bash
=${string_1: -length}
```

```bash
string_1="012345" substring=${string_1:2} echo "$substring"
```

--------------------------------

### Show Current Date

Source: https://speedsheet.io/s/bash

Displays the current system date and time in a default format.

```bash
date
```

--------------------------------

### Identifier Regex Pattern

Source: https://speedsheet.io/s/bash?q=fundamentals-only

This regex defines the valid format for Bash identifiers: starting with a letter or underscore, followed by letters, digits, or underscores.

```regex
[_a-zA-Z][_0-9a-zA-Z]*
```

--------------------------------

### List Top Processes by Memory Usage

Source: https://speedsheet.io/s/bash

Lists the top applications by memory usage.

```bash
top -a
```

--------------------------------

### List Open Ports

Source: https://speedsheet.io/s/bash

Lists all open ports on the computer that are listening for connections.

```bash
netstat -tupln
```

```bash
netstat -an | grep "LISTEN"
```

--------------------------------

### Set IFS Delimiter

Source: https://speedsheet.io/s/bash

Changes the Internal Field Separator (IFS) delimiter characters. This example demonstrates setting IFS to a comma and then restoring it.

```bash
IFS = 'new_characters'
IFS="\n"
old_ifs="$IFS" IFS="," echo "${dict_1[*]}" IFS="$old_ifs"
```

--------------------------------

### Get Current User Name via Environment Variable

Source: https://speedsheet.io/s/bash?q=user-only

Retrieves the current user's name by accessing the USER environment variable.

```bash
echo "$USER"
```

--------------------------------

### Set Prompt to Date

Source: https://speedsheet.io/s/bash

Sets the prompt to display the current date in the format 'Mon Jan 01'.

```bash
PS1=\d
```

--------------------------------

### Set Prompt to Full Current Path

Source: https://speedsheet.io/s/bash

Sets the prompt to display the complete, absolute path of the current working directory.

```bash
PS1=\w
```

--------------------------------

### String to SHA256 Hash using sha256sum

Source: https://speedsheet.io/s/bash

Converts a string to its SHA256 hash using the sha256sum command-line utility. Requires sha256sum to be installed.

```bash
echo "$string_1" | sha256sum
```

--------------------------------

### String to SHA256 Hash using OpenSSL

Source: https://speedsheet.io/s/bash

Converts a string to its SHA256 hash using the OpenSSL command-line tool. Requires OpenSSL to be installed.

```bash
echo "$string_1" | openssl dgst -sha256
```

--------------------------------

### Connect to a Server via SSH

Source: https://speedsheet.io/s/bash

Establishes a secure terminal connection to a remote server. Use the -i option to specify an identity file for authentication.

```bash
ssh user_id@server_url
```

```bash
ssh -i server_pem_file user_id@server_url
```

--------------------------------

### Set Exit Code to True and Check

Source: https://speedsheet.io/s/bash?q=boolean-only

Sets the exit code to 0 using `true` and then demonstrates checking it with `echo "$?"`.

```bash
true
echo "$?"
```

--------------------------------

### Extract Lines N to M from String

Source: https://speedsheet.io/s/bash

Returns a range of lines from a string using `sed -n 'n,mp'`. Line numbers start at 1.

```bash
command | sed -n 'n,mp'
```

--------------------------------

### List Top Processes by Memory Usage

Source: https://speedsheet.io/s/bash?q=processes-only

Use `top -a` to view processes sorted by memory usage. Alternatively, `ps` with specific sorting can achieve the same result.

```bash
top -a
```

```bash
ps -eo pid,%cpu,%mem,vsize,start,args | sort -k 4 -nr | head -25
```

--------------------------------

### Get Last N Lines of String

Source: https://speedsheet.io/s/bash

Returns the last `count` lines of a string. Specify the number of lines using the `-n` option with `tail`.

```bash
command | tail -n count
```

--------------------------------

### Get Last 10 Lines of String

Source: https://speedsheet.io/s/bash

Returns the last 10 lines of a string using the `tail` command. Pipe the string output to `tail`.

```bash
command | tail
```

--------------------------------

### Display Primary Prompt String

Source: https://speedsheet.io/s/bash

Outputs the string used for the primary command prompt.

```bash
$PS1
```

--------------------------------

### Create a File from Script using Stream Literals

Source: https://speedsheet.io/s/bash?q=files-only

Use stream literals (e.g., `<< END_LABEL`) within a script to create a file with multi-line content.

```bash
cat > file_name << END_LABEL ...content... ...content... ...content... END_LABEL
```

--------------------------------

### Set Prompt to Time (HH:MM AM/PM)

Source: https://speedsheet.io/s/bash

Sets the prompt to display the current time in 12-hour format with AM/PM indicator.

```bash
PS1=\@ 
```

--------------------------------

### Show Symbolic Link Target

Source: https://speedsheet.io/s/bash?q=files-only

Displays the target file or directory that a symbolic link points to.

```bash
ls -l link_name
```

--------------------------------

### View Memory Allocation By Type

Source: https://speedsheet.io/s/bash

Displays detailed memory information, including allocation for different memory types on the system.

```bash
cat /proc/meminfo
```

--------------------------------

### Multiline Statement Example

Source: https://speedsheet.io/s/bash?q=fundamentals-only

Use a backslash '\' at the end of a line to indicate that the statement continues on the next line. This improves readability for long commands or strings.

```bash
echo "Part 1 and " \ 
"part 2 and " \ 
"part 3."
```

--------------------------------

### Display Host Name

Source: https://speedsheet.io/s/bash

Outputs the hostname of the computer the script is running on.

```bash
$HOSTNAME
```

--------------------------------

### Run Multiple Commands Sequentially

Source: https://speedsheet.io/s/bash?q=command-execution-only

Use ';' to separate and execute multiple commands in a single line.

```bash
echo "Hello"; echo "There"

```

--------------------------------

### Extract File Name Without Extension or Directory

Source: https://speedsheet.io/s/bash?q=files-only

Combine `basename` and parameter expansion `${file_name%.*}` to get the base file name without extension or path.

```bash
base_name="$(basename "${file_name%.*}")"
```
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