Jason's Notebook

Basics of Terminal

3 min read

Terminal Basics

The terminal is a text-based interface that interprets commands and outputs results.

  • echo: Displays the string provided to it.
    • Example: echo "Hello World" outputs Hello World.
  • pwd (Print Working Directory): Prints the absolute path of your current location.
    • Example: pwd → C:/Users/jason.
  • ls: Lists the files and folders contained within the current directory.

Previewing Files

  • head: Displays the beginning of a file.
    • Default (10 lines): head orders.tsv
    • Custom count: head -n 3 orders.tsv (Prints first 3 lines)
  • tail: Displays the end of a file.
    • Default (10 lines): tail orders.tsv
    • Custom count: tail -n 3 orders.tsv (Prints last 3 lines)
  • cat: Returns and displays the entire content of a file.

Data Filtering and Pipelines

Unix commands can be combined to filter data and store results.

Searching with grep

The grep command generates lists based on filtering properties.

  • Standard: grep "Burrito" orders.tsv (Case-sensitive search).
  • Case-Insensitive: grep -i "burrito" orders.tsv (Ignores casing).
  • Invert Search: grep -v "Burrito" orders.tsv (Finds lines without the term).

Connecting Commands

  • Pipes (|): Directs the output of the left command to the input of the right command.
    • Example: grep -v "Burrito" orders.tsv | tail -n 3
  • Redirection (>): Saves the result of an analysis into a specific file.
    • Example: grep "Burrito" orders.tsv > burritos.tsv
  • File Copying (cp): Copies content from one file to another.
    • Example: cp ref.fa.bak ref.fa

Environment Variables

Variables store data for use throughout the terminal session.

  • Assignment: Use = with no spaces around it.
    • Example: abc=123
  • Retrieval: Use the $ delimiter to call the variable.
    • Example: echo $abc
  • Deletion: Use the unset command.
    • Example: unset abc
  • Listing: Use env to see all active environment variables.

Compiling C++ Programs

C++ source code is converted into an executable using the g++ compiler.

Standard Compilation

For a file named HelloWorld.cpp:

  1. Compile: g++ HelloWorld.cpp (Creates a default file named a.out).
  2. Execute: ./a.out.
  3. Named Output: Use the -o flag to specify the executable name.
    • g++ -o hello_world HelloWorld.cpp
    • ./hello_world

Build Automation with Makefiles

Makefiles organize the compilation of complex projects with multiple files. They track modifications and only recompile necessary components.

General Syntax:

target: dependencies
	system command

Note

System commands must be indented with a Tab character.

Example: Multiple Dependencies If HelloWorld.cpp depends on PrintWords.cpp:

all: hello_world

hello_world: HelloWorld.o PrintWords.o
	g++ -o hello_world HelloWorld.o PrintWords.o
	
HelloWorld.o: HelloWorld.cpp
	g++ -c HelloWorld.cpp
	
PrintWords.o: PrintWords.cpp
	g++ -c PrintWords.cpp
	
clean:
	rm *.o hello_world

Using the Makefile:

  1. Build: Run make (Executes the first target, all).
  2. Execute: Run ./hello_world.
  3. Maintenance: Run make clean to remove compiled object files and binaries.

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