Learning Linux Commands

linux-commands.md

Linux Notes(TechWorld with NANA)

These notes move from basic commands to more advanced command composition. The goal is to understand how simple commands combine to form powerful pipelines.

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Basic Shell Symbols

.

Represents the current working directory.

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-

Used to pass optional parameters (flags) to commands to modify their behavior.

Example: ls -R

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|

Pipe operator.

Used to chain commands together.
The output of the command on the left becomes the input of the command on the right.

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*

Wildcard character.

Matches any number of characters in filenames.

Example: rm *.cpp

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xargs

Takes the output from the left side of a pipe and passes it as arguments to the command on the right, one by one.

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>

Output redirection.

Sends the standard output of a command into a file.
Overwrites the file if it already exists.

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>>

Output redirection (append).

Appends output to a file if it exists.
Creates the file if it does not exist.

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\

Escape character.

Forces the shell to treat the next character literally.

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;

Command separator.

Marks the end of one command and begins another.

Example: mkdir test; cd test

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{}

Placeholder used with the -exec option of the find command.
Represents the currently matched file.

Must be followed by \;

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Commands (Building from Simple to Advanced)

1. ls

Lists files and directories in the current working directory.

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2. ls <folder_name>

Lists files and directories inside the specified folder.

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3. ls -R

Lists files and directories recursively (includes subdirectories).

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4. find . -type d

Lists only directories inside the current directory (recursively).
Does not list files.

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5. grep ""

Filters input and prints lines containing the given string.

Used mostly with pipes.

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6. find . -type f -name "*.cpp"

Finds all files in the current directory (recursively)
that:

• are regular files (-type f)
• have extension .cpp

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7. cat <file_path>

Prints the content of a file to the terminal.

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8. find . -type f -name "*.cpp" | xargs cat

Step-by-step logic:

• find gets all .cpp files
• xargs passes each file to cat
• cat prints their content

This is the first example of command chaining.

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9. find . -type f -name "*.cpp" | xargs cat | grep "int"

Building further:

• Find all .cpp files
• Print their content
• Filter only lines containing the word "int"

This shows how commands combine progressively.

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10. sort

Sorts input lexicographically (alphabetical order).

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11. sort -k3

Sorts lines based on the third column (field).

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12. uniq

Removes duplicate consecutive lines.
Best used after sort.

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13. uniq -f3

Skips the first three fields and checks uniqueness starting from the fourth field.

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14. mkdir <folder_path>

Creates a directory in the specified path.

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15. cp <src_directory> <dest_directory>

Copies files or directories from source to destination.

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16. find . -type f -name "*.cpp" -exec rsync -R {} <dest_folder> ;

Step-by-step logic:

• find locates .cpp files
• -exec runs a command on each file
• {} represents the current file
• rsync -R copies files while preserving directory structure
• \; marks the end of the exec command

This is a more advanced way to operate on matched files.

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17. rm *.cpp

Removes all files ending with .cpp in the current directory.

Uses wildcard *.

Be careful — deletion is permanent.

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Key Idea

Linux becomes powerful when you combine small, simple commands:

find → pipe → process → filter → sort → unique → redirect

Understanding composition is more important than memorizing commands.