Batch Rename

To rename avatar-01.png to placeholder__avatar-01.png

for file in avatar-*.png ; do mv "$file" "placeholder__${file}" ; doneCopy

Color Console Logs

console.log(`\x1b[38;2;0;200;0m${value}\x1b[0;m`)Copy

\x1b[ and \x1b[ are the delimeters

38; or 48; for text vs block colors

2;0;200 are rgb values

0m ends the first part

0;m at the end resets the console

Create File

touch [filename with path]Copy

To create multiple files at once:

touch file-{1,2}.extCopy

Make Directory

mkdir [directory name]Copy

Use the -p flage for nested directory creation:

mkdir -p directory/subdirectoryCopy

Copy

# cp -rv (recursive, verbose) /source/folder/* /destination/folder/
cp -rv "/home/user/Documents/"* "/home/user/Backup/"Copy

Delete Directory

To delete a directory in bash, you can use the rm command with the -r (recursive) flag if the directory is not empty. Here are the commands:

Delete a non-empty directory:

rm -r /path/to/directoryCopy

Delete a directory and avoid confirmation prompts (use with caution):

rm -rf /path/to/directoryCopy

Delete an empty directory:

rmdir /path/to/directoryCopy

Notes:

• rm -r deletes the directory and its contents (files and subdirectories).
• rm -rf does the same but forces the operation without prompting for confirmation.
• rmdir can only delete empty directories.

Change Permissions

Command: chmod +x {file}

chmod:

What it does: Changes file permissions. Full Form: Change Mode. Usage: Modifies who can read, write, or execute a file.

+x:

What it does: Adds the “execute” permission to the file for the user. Symbol Breakdown: +: Adds a permission. x: Represents the execute permission, which allows the file to be run as a program or script.

{file}:

What it is: The name of the file to which you’re applying the permission change. File extension (.sh): Indicates this is a shell script file. What Happens? Running chmod +x {file}.sh:

Adds the execute permission to the file {file}.sh, making it runnable as a script. Result of Permissions: Before: The file might have permissions like -rw-r—r— (read/write but not executable). After: The file changes to -rwxr-xr-x (read/write/execute for you, and read/execute for others). Testing Permissions: To check a file’s permissions, use:

bash ls -l {file}.sh Example output after running chmod +x:

plaintext -rwxr-xr-x 1 username group 1234 Nov 17 12:34 {file}.sh

Make a shell script

Steps to Create the Script Create the Script File:

Open a terminal and create a new file (e.g., update_yaml.sh):

nano update_yaml.shCopy

Add the Script Content: Paste the corrected script into the file:

#!/bin/bashCopy

A script to update the YAML front matter in markdown files

for file in *.md; do
  date=$(date +"%Y-%m-%d")  # Capture the current date
  filename="${file%.md}"    # Remove .md extension from the file name
  awk -v date="$date" -v layout="../../layouts/PostLayout.astro" -v title="$filename" '
    BEGIN { inside_block = 0 }
    /^---$/ {
      if (inside_block == 0) {
        inside_block = 1
        print "---"
        print "layout: " layout
        print "publishedDate: " date
        print "title: " title
        print "author: Elliot Reed"
      } else {
        inside_block = 0
        print "---"
      }
      next
    }
    !inside_block { print }
  ' "$file" > temp && mv temp "$file"
doneCopy

Make the Script Executable: After saving the file, make it executable:

chmod +x update_yaml.shCopy

Move the Script to a Directory in Your PATH (Optional):

To make the script globally accessible, move it to a directory like /usr/local/bin:

sudo mv update_yaml.sh /usr/local/bin/update_yamlCopy

You can now trigger the script with the command update_yaml from any directory. How to Run the Script Navigate to the Directory with .md Files:

cd /path/to/markdown/filesCopy

Execute the Script:

If the script is in the current directory:

./update_yaml.shCopy

If the script was moved to a directory in your PATH:

update_yamlCopy

Optional Enhancements Accept Directory or File Patterns: Modify the script to take an optional directory or file pattern:

# Default to current directory if no argument is given
target_dir=${1:-.}
for file in "$target_dir"/*.md; do
  ...
doneCopy

Run it like this:

update_yaml /path/to/filesCopy

Backup Files Before Modifying: Add a backup step to ensure original files are not lost:

cp "$file" "$file.bak"Copy

Append Text

echo "some text" >> .gitignoreCopy

Syntax

Quotes

Double Quotes (”)

Preserve the literal meaning of most characters inside them, except for $, , `, and !. Allow variable substitution and command substitution.

echo "Hello, $name"  # Substitutes the value of $nameCopy

Single Quotes (’)

Preserve the literal meaning of all characters inside them. Nothing is interpreted.

echo 'Hello, $name'  # Outputs: Hello, $nameCopy

Dollar Sign ($)

Used to reference variables or perform command substitution.

echo $name  # Refers to a variable named `name`
date=$(date)  # Command substitution: captures the output of `date`Copy

Parentheses

Round Parentheses (())

Used in arithmetic expressions or to define subshells.

result=$((3 + 5))  # Arithmetic: Adds 3 and 5
(cd /tmp && ls)    # Subshell: Executes `cd` and `ls` without changing the parent shellCopy

Square Brackets ([])

Used in conditional tests.

if [ $x -gt 5 ]; then  # Tests if `x` is greater than 5Copy

Double Square Brackets ([[]])

Enhanced test syntax (```bash-specific), supports regex and logical operators.

if [[ $x =~ ^[0-9]+$ ]]; then  # Tests if `x` matches a numeric regexCopy

Braces ({})

Used for grouping commands, variable expansion, or ranges.

echo ${name}_suffix     # Variable expansion with a suffix
for i in {1..5}; do     # Range: Loops from 1 to 5Copy

Pound Sign (#)

Marks the start of a comment in shell scripts.

# This is a commentCopy

Special Syntax in Your Script

$((…)) Arithmetic evaluation.

imageIndex=$(( (imageIndex + 1) % imageCount ))  # Cyclic incrementCopy

${} Expands the value of a variable and allows additional syntax (like default values).

${#images[@]}  # Returns the number of elements in the `images` arrayCopy

$(…) Command substitution: Captures the output of a command.

date=$(date +"%Y-%m-%d")  # Runs `date` and assigns its output to the variableCopy

Inside ${#var}, gets the length of a variable or an array.

${#images[@]}  # Length of the `images` array
> temp && mv temp "$file"Copy

Redirects output to temp, and if successful (&&), renames temp to the original file.