linux-odyssey/quests/execute/en/execute.md

Running Executable Files

Outline

1. What an executable file is
2. How to find an executable with which
3. How to run an executable file

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In earlier lessons, you used commands such as ls, cat, cp, mv, and rm. These commands are executable files that the operating system runs when you enter them. For most commands, you can find the corresponding file in the file system. Use which to find the file associated with a command. Enter which [command name] to display its path.

Use which ls to find the path to ls

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The terminal displays /usr/bin/ls, the location of the ls executable. /usr/bin is a system folder containing many standard programs, including commands such as cat and cp.

Use which cat to find the path to cat

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To run an executable file, enter its path directly. Let's try running a command using the path to its executable.

Enter /usr/bin/ls to list the contents of your current folder

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It lists the files in your folder, just as entering ls does. You can compare the results yourself. You can still pass arguments. Let's try this with cat.

Enter /usr/bin/cat hello.txt to display the contents of hello.txt

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You can see the contents of hello.txt, just as you would with cat. This makes sense: cat is located at /usr/bin/cat, so both commands run the same program. A command like this consists of an executable plus arguments. You can enter ls instead of /usr/bin/ls because the PATH environment variable tells the terminal which folders to search for programs. PATH and environment variables are beyond this lesson's scope. We will cover them in a future lesson.

You can also run custom programs, such as the dog file in your current folder.

Use cat dog to display the contents of dog

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This is a simple program built from echo and sleep commands. You do not need to understand every detail yet. It prints a few lines of text, with short pauses between them.

To run a file, specify its path. Since dog is in your home folder, its absolute path is /home/commander/dog. You can also use the shorter form ~/dog.

Enter ~/dog to run the dog file

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The terminal displays a few words from this dog with an attitude. When you are in the same folder as a program, a relative path is often more convenient than an absolute path. To run a program in your current folder, put ./ before its filename instead of entering just its name. In a path, . means the current folder. Now try running dog using a relative path.

Enter ./dog to run the dog file

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The dog produces the same output as before. This is an example of a simple custom command. You can put a sequence of commands in a file and run them together to handle complex or repetitive tasks. This technique is also useful when running programs written by other people.

Here is a final challenge: enter the commands folder, then run the lucky file inside it using a relative path.