Please enable JavaScript.

Coggle requires JavaScript to display documents.

Command Line (Commands (Redirection (grep (grep -Rl (Searches all files in…

- - - - Run programs
      - Write scripts to automate common tasks
      - Combine simple commands to operate to handle difficult tasks
- - - - When typed: the command line looks at the folder you are in, and then "lists" the files and folders inside it.
      - Options:
        
        ls -a
        
        Lists all contents, including hidden files and directories
        
        The -a is called an option
        
        DEFINITION Option: modify the behavior of commands.
        
        Modifies the behavior of the ls command to also list the files and directories starting with a dot (.), which don't appear when using ls alone.
        
        ls -l
        
        Lists all contents of a directory in long format
        
        Lists files and directories as a table.
        
        e.g.
        
        Columns:
        
        1. Access rights
        
        Actions that are permitted on a file or directory.
        
        2. Number of hard links
        
        This number counts the number of child directories and files. This number includes the parent directory link (..) and current directory link (.).
        
        3. The username of the file's owner.
        
        4. The name of the group that owns the file.
        
        5. The size of the file in bytes
        
        6. The date & time that the file was last modified.
        
        ls -t
        
        order files and directories by the time they were last modified.
        
        ls -alt
        
        lists all contents, including hidden files and directories, in long format, ordered by the date and time they were last modified.
    - - "print working directory"
      - Outputs the name of the directory you are currently in, called the working directory.
      - Useful to show where you are in the filesystem.
    - - "change directory"
      - Switches you into the directory you specify
      - i.e. changes the working directory.
      - Takes a directory name as an argument, and switches into that directory
      - e.g.
      - Navigate directly to a directory:
        
        Use cd with the directory's path as an argument.
        
        e.g. navigates directly to the jan/memory directory
      - Move up one directory:
        
        use cd ..
        
        e.g. navigates up from jan/memory/ to jan/.
    - - "make directory"
      - Takes in a directory name as an argument, and then creates a new directory in the current working directory.
    - - Creates a new file inside the working directory.
      - Takes in a filename as an argument, and then creates an empty file in the current working directory.
      - e.g. used touch to create a new file named keyboard.txt inside the 2014/dec/ directory.
  - - - Copies files or directories.
      - Copy contents of one file into another
        
        e.g. copies the contents of frida.txt into lincoln.txt.
      - Copy a file into a directory
        
        Use cp with the source file as the first argument and the destination directory as the second argument.
        
        e.g. copies the file biopic/cleopatra.txt and place it in the historical/ directory.
      - Copy multiple files into a directory
        
        Use cp with a list of source files as the first arguments, and the destination directory as the last argument.
        
        e.g. copies the files biopic/ray.txt and biopic/notorious.txt into the historical/ directory.
      - Wildcards
        
        Special characters used to select groups of files.
        
        *
        
        Selects all files in the working directory
        
        e.g. uses cp to copy all files into the satire/ directory.
        
        e.g. **m.txt selects all files in the working directory starting with "m" and ending with ".txt", and copies them to scifi/*.
    - - Moves files.
      - Similar to cp in usage
      - Move multiple files into a directory
        
        Use mv with a list of source files as the first arguments, and the destination directory as the last argument.
        
        e.g. move wonderwoman.txt and batman.txt into superhero/.
      - Move a file into a directory
        
        e.g. move superman.txt into superhero/.
        
        Use mv with the source file as the first argument and the destination directory as the second argument.
      - Rename a file
        
        Use mv with the old file as the first argument and the new file as the second argument.
        
        e.g. By moving batman.txt into spiderman.txt, we rename the file as spiderman.txt.
    - - Deletes files and directories.
      - Removing files
        
        e.g. Here we remove the file waterboy.txt from the filesystem.
      - rm -r
        
        Modifies the behavior of the rm command.
        
        The -r stands for "recursive".
        
        Used to delete a directory and all of its child directories.
      - WARNING:Be careful when you use rm! It deletes files and directories permanently. There isn't an undelete command, so once you delete a file or directory with rm, it's gone.
  - - - Standard input
      - Information inputted into the terminal through the keyboard or input device.
    - - Standard output
      - The information outputted after a process is run.
    - - Standard error
      - An error message outputted by a failed process.
    - - Redirects the standard output to a file.
        
        e.g.
        
        Standard input: "Hello"
        
        Standard output: "Hello" - redirected by > to the file hello.txt.
        
        cat
        
        Outputs the contents of a file to the terminal.
        
        When you type cat hello.txt, the contents of hello.txt are displayed.
        
        Takes the standard output of the command on the left, and redirects it to the file on the right.
        
        e.g.
        
        Here the standard output of cat oceans.txt is redirected to continents.txt.
        
        Overwrites all original content in continents.txt.
        
        When you view the output data by typing cat on continents.txt, you will see only the contents of oceans.txt.
    - - Takes the standard output of the command on the left and appends (adds) it to the file on the right.
      - You can view the output data of the file with cat and the filename.
      - e.g. Here, the output data of rivers.txt will contain the original contents of rivers.txt with the content of glaciers.txt appended to it.
    - - Takes the standard input from the file on the right and inputs it into the program on the left.
      - e.g. Here, lakes.txt is the standard input for the cat command. The standard output appears in the terminal.
    - - Pipe
      - Takes the standard output of the command on the left, and pipes it as standard input to the command on the right.
      - You can think of this as "command to command" redirection.
      - e.g.
        
        The wc command outputs the number of lines, words, and characters in volcanoes.txt, respectively.
        
        Here the output of cat volcanoes.txt is the standard input of wc. in turn,
      - Chaining multiple |'s together
        
        e.g.
        
        Here the standard output of cat volcanoes.txt is "piped" to the wc command.
        
        The standard output of wc is then "piped" to cat.
        
        Finally, the standard output of cat is redirected to islands.txt.
    - - Takes the standard input and orders it alphabetically for the standard output.
      - e.g. Here, the lakes in sort lakes.txt are listed in alphabetical order.
      - e.g.
        
        Here, the command takes the standard output from cat lakes.txt and "pipes" it to sort.
        
        The standard output of sort is redirected to sorted-lakes.txt.
    - - Filters out adjacent, duplicate lines in a file.
      - "Unique"
      - e.g.
        
        Here uniq deserts.txt filters out duplicates of "Sahara Desert", because the duplicate of 'Sahara Desert' directly follows the previous instance.
        
        The "Kalahari Desert" duplicates are not adjacent, and thus remain
      - e.g.
        
        A more effective way to call uniq is to call sort to alphabetize a file, and "pipe" the standard output to uniq.
        
        i.e. 1. sort, 2. uniq
        
        Here by piping sort deserts.txt to uniq, all duplicate lines are alphabetized (and thereby made adjacent) and filtered out.
    - - "global regular expression print"
      - Searches files for lines that match a pattern and returns the results.
      - Case sensitive.
      - e.g. Here, grep searches for "Mount" in mountains.txt.
      - grep -i
        
        Enables the command to be case insensitive.
        
        e.g. grep searches for capital or lowercase strings that match Mount in mountains.txt.
      - grep -R
        
        Searches all files in a directory and outputs filenames and lines containing matched results.
        
        e.g. Here grep -R searches the /home/ccuser/workspace/geography directory for the string "Arctic" and outputs filenames and lines with matched results.
      - grep -Rl
        
        Searches all files in a directory and outputs only filenames with matched results.
        
        -R stands for "recursive" and l stands for "files with matches".
        
        e.g. Here grep -Rl searches the /home/ccuser/workspace/geography directory for the string "Arctic" and outputs filenames with matched results.
    - - "stream editor"
      - Accepts standard input and modifies it based on an expression, before displaying it as output data.
      - It is similar to "find and replace".
      - e.g. 's/snow/rain/'
        
        s:
        
        Always used when using sed for substitution.
        
        "substitution"
        
        snow:
        
        The search string, the text to find.
        
        rain:
        
        The replacement string, the text to add in place.
      - sed searches forests.txt for the word "snow" and replaces it with "rain."
      - IMPORTANT: the above command will only replace the first instance of "snow" on a line.
      - e.g.
        
        The above command uses the g expression, meaning "global".
        
        Here sed searches forests.txt for the word "snow" and replaces it with "rain", globally.
        
        All instances of "snow" on a line will be turned to "rain".
  - - - A command line text editor
      - It works just like a desktop text editor like TextEdit or Notepad, except that it is accessible from the command line and only accepts keyboard input.
      - e.g.
        
        opens a new text file named hello.txt in the nano text editor.
        
        a text string entered in nano through the cursor.
        
        3. Menu of Commands
        
        The ^ stands for the Ctrl key.
        
        Ctrl + O saves a file. 'O' stands for output.
        
        Ctrl + X exits the nano program. 'X' stands for exit.
        
        Ctrl + G opens a help menu.
        
        Clear: clears the terminal window, moving the command prompt to the top of the screen.
      - The Bash Profile
        
        ~/.bash_profile is the name of file used to store environment settings.
        
        When a session starts, it will load the contents of the bash profile before executing commands.
        
        ~ represents a user's home directory
        
        . indicates a hidden profile
        
        e.g.
        
        Opens up ~/.bash_profile in nano.
        
        text
        
        Creates a greeting in the bash profile, which is saved.
        
        It tells the command line to echo the string "Welcome, Jane Doe" when a terminal session begins.
        
        Command
        
        Activates the changes in ~/.bash_profile for the current session.
        
        Instead of closing the terminal and needing to start a new session, source makes the changes available right away in the session we are in.
        
        The name ~/.bash_profile is important, since this is how the command line recognises the bash profile.
      - alias
        
        Command that allows you to create keyboard shortcuts, or aliases, for commonly used commands.
        
        When you store this alias in ~/.bash_profile
        
        e.g.
        
        Creates the alias pd for the pwd command, which is then saved in the bash profile.
        
        Command that makes the alias pd available in the current session.
        
        Each time we open up the terminal, we can use the pd alias.
        
        history
        
        A command that outputs a history of commands that were entered in the current session.
        
        e.g.
        
        hy is set as alias for the history command in the bash profile.
        
        The alias is then made available in the current session through source.
        
        By typing hy, the command line outputs a history of commands that were entered in the current session.
        
        e.g.
        
        ll is set as an alias for ls -la and made available in the current session through source.
        
        By typing ll, the command line now outputs all contents and directories in long format, including all hidden files.
      - The Environmental Variables
        
        Variables that can be used across commands and programs and hold information about the environment.
        
        export
        
        e.g. When you store in ~/.bash_profile
        
        At the command line, the command echo $USER returns the value of the variable. Note that $ is always used when returning a variable's value. Here, the command echo $USER returns the name set for the variable.
        
        The line USER="Jane Doe" sets the environment variable USER to a name "Jane Doe". Usually, the USER variable is set to the name of the computer's owner.
        
        Makes the variable to be available to all child sessions initiated from the session you are in. This is a way to make the variable persist across programs.
        
        e.g. When is stored in ~/.bash_profile
        
        PS1
        
        a variable that defines the makeup and style of the command prompt.
        
        export PS1=">> " sets the command prompt variable and exports the variable. Here we change the default command prompt from $ to >>.
        
        After using the source command, the command line displays the new command prompt.
        
        HOME
        
        An environment variable that displays the path of the home directory.
        
        e.g. the terminal displays the path /home/ccuser *as output.
        
        You can customize the HOME variable if needed, but in most cases this is not necessary.
        
        PATH
        
        An environment variable that stores a list of directories separated by a colon.
        
        e.g. Looking carefully, echo $PATH lists the following directories:
        
        /home/ccuser/.gem/ruby/2.0.0/bin
        
        /usr/local/sbin
        
        /usr/local/bin
        
        /usr/bin
        
        /usr/sbin
        
        /sbin
        
        /bin
        
        Each directory contains scripts for the command line to execute.
        
        The PATH variable simply lists which directories contain scripts.
        
        Many commands are scripts stored in the /bin directory.
        
        e.g. This is the script that is executed when you type the pwd command.
        
        e.g. This is the script that is executed when you type the ls command.
        
        In advanced cases, you can customise the PATH variable when adding scripts of your own.
        
        env
        
        "environment"
        
        Command
        
        Returns a list of the environment variables for the current user.
        
        Here, the env command returns a number of variables, including PATH, PWD, PS1, and HOME.
        
        e.g.
        
        A command that displays the value of a single environment variable.
        
        Here the standard output of env is "piped" to the grep command.
        
        grep searches for the value of the variable PATH and outputs it to the terminal.
- - - - The first directory in the filesystem
      - The parent of all other directories and files in the filesystem.
    - - Can contain more child directories and files.
    - - Each directory can contain more files and child directories.
      - The parent-child relationship continues as long as directories and files are nested.