linux-command-reference

All Commands and Shortcuts:

• 📋 IT-Tools Bash Cheatsheet

Reference for Linux Commands

• 🖋️ uname: Print basic info about system OS and hardware. Options
• 📍 pwd: Print working directory, where are we located.
• 📂 cd: Change working directory.
• 📋ls: Lists / displays contents of a directory. Shows files and directories within the current directory. Options
• 🐈‍⬛ cat: Concatenate: Read the contents of any file. Options
• 🔍 grep: General Regular Expression Print: Search for text patterns in files or output. Filters and displays lines that match a specific string or patttern. Options
• 📮 cp: Copy files from one directory to another cp [SOURCE] [DESTINATION] Options
• 💯 wc: Word Count: Count number of lines, words, characters in a file or some input. Options
• 🔍 find: Search for Files and direcories. find [starting_path] [option] [expression]. Options
• 🚦 diff: Compare two files and show the difference. diff file1 file2 Options
• 🕸️ curl: Client URL. Used to transfer data from or to a server using HTTP or other protocols. Typically used to interact with APIs. Options
• 📝 vim: Open VIM Editor to change files. Options
• ✍️ chmod: Change Mode: Modify file permissions. Options
• ✋ touch: Create files or update the timestamps. touch [options] [file_name(s)] Options

🎥 Good References / Sources

1. 📼 TechWorld with Nana - 13 Linux Commands: Mentioned Commands:
   • uname, pwd, cd, ls, cat, grep, cp, wc, find, diff, curl, vim, chmod
2. 📋 Linux Commands Cheat Sheet
3. ﹥ Other CLI Tools 10 CLI apps Video

📋 Extended Reference - Commands' Options

uname

• -a All System Information
• -s Kernel name (default)
• -r Kernel release
• -v Kernel version
• -m Machine hardware architecture / name (ex., x86_64)
• -n Network hostname
• -o Operating system
• -p Processor type

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ls

Most Used

• -l Long format: Shows files details: permisions, owner, size and modification date.
• -h Displays file sizes in human-readable formats (e.g., KB, MB) when combined with -l.
• -t Sorts files by modification time, with the newest first.

Others

• -a All files, including hidden ones.
• -R Lists contents of directories recursively, including subdirectories.
• -r Reverses the order of the output.
• -1 Lists one file per line instead of displaying them in columns.
• -d Lists directories only.
• -F Appends a character to filenames indicating their type (e.g., / for directories, * for executables).
• -X Sorts files alphabetically by their extension.

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cat

• -n: Displays the output with line numbers.
• -E: Displays a $ character at the end of each line.
• -s: Squeezes multiple adjacent empty lines into one.

You can join multiple files into a new file:

cat file1.txt file2.txt > merged.txt

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grep

• Searching within a specific file:

grep dog sample.txt

• When searching for phrases use "":

grep "connection refused" sample.txt

• -i makes the search case-insensitive.
• -c display the count of matches.
• Use regex for more advanced seach patterns. Lines that start with Hello for example:

grep "^Hello" -i sample.txt

• More complex search examples 🗒️ Search Patterns Examples

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cp

Examples

Simple Copy

cp file1.txt file1_copy.txt

Copy to another Directory, passing the direct path:

cp file1.txt /root/file1_copy.txt

Also used to copy directories:

cp -r dir1 dir2

• -r used to copy directories recursively, including internal files.
• -p preserve the original file attributes and timestamps

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wc

• -l Count Lines
• -w Count Words
• -c Bytes
• -m Characters
• -L find longest Line Length

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find

• Options: You can search by name, file type, file size or permission.
• -type: f file, d directory.
• -size: Finding by size, using + and - prefixes signifying greater than and less than. 'M' for mebibytes, 'G' for gibibytes, 'k' for kibibytes.
• Examples: "."= Current Directory. "/"= Entire File System. Root file system.

find -name / "*.conf"
# Combine with grep to filter:
find -name / "*.conf" | grep db
find -name / "*.conf*" | grep db
# Larger files:
find . -size +1M

More info: Linux Manual on Find

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diff

• -c: Display the differences in a more readable format.
• -w: Ignore white space differences.

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curl

• -I (or --head): Just return the headers. (Metadata)
• -O Tells curl to save the file with the same name as the remote file.
• -o To specify a different file name.

curl https://google.com
curl http://localhost:5432

curl -o curl_homepage.html https://google.com

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vim

• Commonly used for editing config files in Linux
• It has 3 modes
  • Insert Mode: type or edit text.
  • Normal Mode: Default, for navigation
  • Command Mode: Execute commands like save, quit, search.

vim db.config

Navigation:

• To enter edit mode, press i.
• To Exit: Press ESC (Back to normal mode) then ":" and:
  • :q Quit only if no changes have been made.
  • :q! Quit without Saving
  • :w Save the file
  • :wq or ZZ
  • x Save and quit only if changes were made.

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chmod

• File Permissions

  • Initial symbol: - File, d Directory, l Sybolic Link
  • Different types: -rwxrwxrwx: Read, Write, Execute, - is denied.
  • Position is in this order: User, Group, Other. so -rw-rw--- means User and Group can only read and write.
  • To change permissons each permission has a numeric value: r=4, w=2, x=1

## Full Permissions
chmod 777 db.config
## No Permissions
chmod 000 db.config
## Read Permissions only for all groups
chmod 444 db.config
## Owner rwx, Group and Others: rx (Good for Scripts)
chmod 755 db.config
## Owner rw, Group and Others: r (Usually Text files)
chmod 644 db.config

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touch

• -a: Updates the access time of the file.
• -m: Updates the modification time of the file.
• -d or -t: Sets the access and modification times to the specified date and time.
• -c or -f: Creates the file if it doesn't exist, without issuing an error message.

touch new_file.txt

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Other

Chain multiple commands using the | (pipe) operator. Whatever the first command outputs it will be the input of the following command.

## Chain Commands
cat file1.txt | grep Database

Output functions result into a textfile using >:

## Output result to a file
cat file1.txt | grep Database > filtered.txt

Append lines to .txt using >.

## Create sample text files
echo "First line of file_1.txt." > file_1.txt
echo "Second line of file_1.txt." >> file_1.txt

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Useful Tools

1. 🛠️ It Tools -> Web Version -> Forked due to non maintenance -> Next Tools -> Web Version