> For the complete documentation index, see [llms.txt](https://doane-ccla.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://doane-ccla.gitbook.io/docs/learning-linux/essential-commands.md). # Essential Commands * [Overview](/docs/learning-linux/essential-commands.md#overview) * [Common Shortcuts](/docs/learning-linux/essential-commands.md#common-shortcuts) * [Basic Commands](/docs/learning-linux/essential-commands.md#basic-commands) * [Pipe and Redirection](/docs/learning-linux/essential-commands.md#pipe-and-redirection) ## Overview * Linux has a hierarchy of directories that lists contents of files in a tree-like format, starting from the file system root (`/`). * Linux is *case-sensitive*, e.g. `Myfile`, `myfile`, `MYFILE`, and `MyFile` are four unique files. * Linux does not require filename extensions such as `.doc`, `.exe`, and `.abc`. The `.` extension is simply part of the filename. Sometimes data files are named with extensions (.hdf, .cdf, .tar) for human readability, though this is optional. * A file with `.` at the beginning will be considered a hidden file. * You can use the `` key to autocomplete commands, paths, and environment variables. For example, you can type `cal` on your terminal followed by `` to test this. If there is more than one option for the autocomplete to choose from, pressing `` *twice* will provide a list of all possible options based on what you have typed. * The `up-arrow` will display the previous command you have typed and if you press the `down-arrow`, it will refer to the following command. * The `history` command will show all of the previous commands you have entered during the last session(s). ## Common Shortcuts | macOS keyboard | Windows keyboard | Action | | -------------- | ---------------- | ----------------------------------------- | | `CMD`+`D` | `CTRL`+`D` | Exit a terminal, same as typing `exit` | | `CMD`+`L` | `CTRL`+`L` | Clears the screen, same as typing `clear` | | `CMD`+`C` | `CTRL`+`C` | Breaks/cancels an ongoing operation | | `CMD`+`Z` | `CTRL`+`Z` | Pauses (stops) an ongoing operation | | `CMD`+`N` | `CTRL`+`N` | Opens a new terminal | 📝 **Note:** If you want to learn more shortcuts, please consult more documentation [here](/docs/learning-linux/shortcuts.md). ## Basic Commands * **pwd: Print Current Working Directory** ```bash pwd /Users/user ``` *The output of* `pwd` *in this case, is the home directory of the user user, which is shown with the complete path starting from root(*`/`*)* * **ls: List the contents of the current directory** ```bash ls Documents/ Pictures/ Desktop/ Downloads/ document.txt ``` *The output is a list of four directories (followed by a* `/`*) and one file. To see information about the contents in a list, type* `ls -l`*.* * **cd: Change directory** ```bash cd Documents ``` *In this case, we are entering the "Documents" directory.* If you want to go directly to your home directory (user), you can type `cd` without any specification of which directory. In the case of nested folders, you can jump one directory level upwards by typing `cd ..` **alias**: In case of deeply nested folders (/path/to/project/com/java/lang/morefiles) that might take more than 4 directory levels upwards, you can create an `alias`, for example, `alias ..2="cd ../.."` or `alias ..3="cd ../../.."` or `alias ..4="cd ../../../.."`. If you wish to make these aliases a permanent feature of your Bash environment, you may add the commands to the end of the `.bashrc` file. Edit the `.bashrc` file by opening it in your favorite text editor (it is located in your home directory). For example, type `vi .bashrc`. * **whoami: Shows the user ID as a name** ```bash whoami user ``` *This shows the username that is logged in to the current session of the machine.* If you need additional information about the user, such as, to which groups they are a member, type `id`. If you want to see all the users that are logged in to the computer, you can type `w`. * **date: Display the date and time of the system** ```bash date Wed Apr 4 09:06:30 EDT 2018 ``` *The date is shown in a complex format.* Use `date +%F` format if you want to do a [backup of a file including the date in the filename](/docs/learning-linux/essential-commands/backup.md). If you want to [calculate, in seconds, the duration of a program](/docs/learning-linux/essential-commands/seconds.md), you can use the `date +%s` command. * **cal: Display a calendar of the current month** ```bash cal ``` *This command displays the calendar of the current month of the year in which the command is executed.* In case you need the whole year calendar of 2018, you may type `cal 2018` or set any other year you want to check. If you want to display any particular month of the year, you can type, for example, `cal March 2018`. To display the Eastern date of the current year, please type `ncal -o`. * **cat: Creates a single or multiple files, views the contents of a file, concatenates files, and redirects output into the terminal or into files** ```bash cat /Users/user/myfile.txt hello world ``` *In this case, we want to display the content of* `myfile.txt` *which is located inside the* `user` *directory.* If we are positioned inside the `user` directory, all that is needed is `cat myfile.txt` to see its contents, which is "hello world". You can view the content of two files at the same time with the `cat file1.txt file2.txt`. In case you need the lines of a text numbered, please type `cat -n myfile.txt`. * **echo: Display a line of text or a string on standard output or into a file** ```bash echo "Hi CCLA" Hi CCLA ``` *In this example, the string* `Hi CCLA` *is shown because we send that message to the terminal.* To view the value assigned to a variable, add `$` before the variable name: (e.g. `x=10; echo "The value of 'x' is: $x"`). If you need a new line `\n`, use the option `-e` (e.g. `echo -e "Hello \n world"`). * **touch: Create a new empty file** ```bash touch myNEWfile ``` *In this case,* `myNEWfile` *was created inside the directory in which you are positioned.* You can create more than one file at the same time with by typing `touch file1 file2`. If you want to create lots of files that share a common string, e.g. `test1.txt`, `test2.txt`, `test3.txt`, and so on until 25, you can use `touch test{1..25}.txt`. * **mkdir: make directory** ```bash mkdir myNEWdir ``` *In this case, a new directory called* `myNEWdir` *is created in the current path.* If you want to set the permission of the directory while you are creating the directory, you can do so by typing `mkdir -m a=rwx myNEWdir`. Here, the letters r, w, and x stand for read, write, and execute, respectively. For more information on file and directory permissions, see [here](https://github.com/Doane-CCLA/docs/tree/0c60589b310fc031c5c0a5c3935362eb9ab107a4/learning-linux/permissions.md). If you want to create multiple directories at once, run `mkdir test1 test2 test3`. If you want to create several subdirectories at one time, type `mkdir -p /home/test/test1/test2/test3/test4`. * **cp: Copy files and directories** ```bash cp /path/to/file_src /path/to/file_dest ``` In this case the contents of `file_src` (source) will be copied to `file_dest` (destination) and both files will be present in both paths. If you need to copy more than one file into a directory, you can type `cp main.c def.h /Users/user/mydir/`. To copy all the files you have (in your current path) with the extension `.c` to a directory called `bak`, you can type `cp *.c bak`. The asterisk (`*`) is a wild-card character. * **mv: Move or rename the files or directories** ```bash mv file1 Myfile1 ``` *The file called* `file1` *was renamed as* `Myfile1`*.* If you want to move all of your C files to a subdirectory called `bak`, you can run `mv *.c bak`. If you want to create a backup when copying your `.txt` files into the `mybak` directory (to not overwrite existing files within `mybak`) use: `mv -bv *.txt /Users/user/mybak`. * **rm: Delete files or directories** ```bash rm file1 Myfile1 ``` *The files called* `file1` *and* `Myfile1` *will be removed.* For directories, the recursive option `-r` is needed, e.g. `rm -r modelOutput`. * **man: Display the manual of the Linux commands** ```bash man sudo ``` *A manual related to the* `sudo` *command is displayed explaining how the* `sudo` *command will grant you privileges to execute commands as the superuser does.* For further information you can do `man man` to read more about `man`. To exit a manual page, type `q`. ## Pipe and Redirection * **| Pipeline** A *pipe* is a form of redirection that sends the output of a program (written *before the pipe*) to another one (written *after the pipe*) for further processing. To make a pipe, put a vertical bar (`|`) on the command line between two commands. ```bash man pipe | cat > /tmp/myMAN.txt ``` *The command* `man pipe` *will display the content of all the information about **pipe**, then **that content** will be processed by* `cat` *(taken as its **input**) and be redirected to the file* `/tmp/myMAN.txt`*. So, the **output**, the content of* `myMAN.txt` *will display the manual information about **pipe**.* * **> Redirecting output** Commands can send and receive streams of data to and from files and devices. ```bash echo "Test report title" > /tmp/test.txt ``` *"Test report title" will be written to the file* `test.txt` *located inside the* `/tmp` *directory.* It is also possible to send all the content of `/tmp/hi.txt` to `/Users/user/hello`, by using `/tmp/hi.txt > /Users/user/hello`. `Mail -s "Subject" to-address@example.com < Filename` will email the content of `Filename`. * **>> Appending (postpending) redirected output** This command will append (postpend) information to where it is designated. ```bash echo "This report was done at $HOSTNAME at $(date+%F)">>/tmp/report.txt ``` *The output of the first part of the command (before the* `>>`*) will be added at the **end** of the file* `/tmp/report.txt`*.* --- # Agent Instructions This documentation is published with GitBook. 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