Linux Command Line Notes

Reference for basic command line commands for Linux, because I always forget a lot of these.

Show current working directory

pwd

See username

whoami

Changing directories

Move to root/top directory

cd /

Move to user home directory

cd ~

or just

cd

Go up one directory level

cd ..

Print to screen

echo "Hello world!"

Creating directories and file

Create new directory

mkdir new_directory

Create multiple directories

mkdir dir1 dir2 dir3 dir4

You can't make new nested directories with mkdir. To do so, use the -p flag for "make parent directories"

mkdir -p new_directory/test_files/dir1

Create new file

touch new_file.txt

Use redirect to create simple files for testing etc. This will create a file if it's not already there. If there is already a file with the same name present, it will overwrite it so be careful!

echo "Hello world" > test.txt

Appending to a file

Using > to add something to a file will overwrite what was there before. Use >> to append to the end of file without overwriting everything.

echo "Appending some text!" >> myfile.txt

View directory contents

List all directories and files in current working directory excluding hidden ones

ls

Also show hidden files:

ls -a

See file permissions and more info (long format)

ls -l

Viewing files

Use cat to simply print the all the contents to the screen

cat config.txt

This can be done with multiple file names to see contents of multiple files

cat config.txt test.txt hello.txt

Use the less pager program to view files in an interactive pager.

less super_long_text.txt

Using Wildcards * and ?

? will match any single character.

For example, if you have multiple files like test_1.txt, test_2.txt and test_3.txt, you could print out all files like so:

cat test_?.txt

* will match zero or more characters.

For example, remove all mp3 files:

rm *.mp3

Moving and renaming files and directories

Use mv to move or rename files

mv <file_to_move> <destination_to_move_it>

Example: move test.txt to the testing directory one level above

mv text.txt ../testing

You can move multiple files/directories at once. List all the files/directories to move first. The last item will serve as the destination directory. The command below will move file.txt, dir1, and file2.txt to the dir2 directory.

mv file.txt dir1 file2.txt dir2

Example: rename test.txt to unit_tests.txt

mv text.txt unit_tests.txt

Example: rename testing directory to unit_tests

mv testing unit_tests

Copying file

Copy to a new directory

cp <file_to_copy> <direcory_to_copy_to>

Example: Make a copy of config.txt in the backup directory

cp config.txt backup

Copy a file to the same directory with a new name

cp <file_to_copy> <new_name_for_copied_file>

Example: Create a copy of essay.txt in the current directory and name it essay_edit.txt

cp essay.txt essay_edit.txt

Removing (Deleting) files and directories

CAUTION: These commands will permanently delete things without a way to retrieve them, so make sure you're very careful!

Delete one or more files

rm test1.txt
rm text2.txt test3.txt

Delete a directory. This only works for empty directories.

rmdir my_folder

Delete a directory and any empty sub-directories using the -p flag. This will not delete files contained in the directories. Below would delete the my_folder directory and any empty subfolders it contains.

rmdir -p my_folder

Remove all directories and files in the given location (Dangerous):

rm -r folder_to_delete

Word and line counts

Show line count, word count, and byte count of a file (in that order)

wc test_1.txt
>   5      10      56 test_1.txt

The above output tells us that test_1.txt has 5 lines, 10 words, and 56 bytes.

To show only line count, use the -l flag

wc -l test_1.txt
>   5 test_1.txt

Sort command

Sort a file by line, that is, matching lines will be grouped together.

sort my_file.txt

Piping

Pipes | allow you to feed the output of one command into the next command.

Example: See how many files/folders there are in the user's home directory

ls ~ | wc -l

ls ~ would list all the files in the directory. Putting a pipe after it feeds the output into the wc word count command.

Example: Count the number of unique lines in a file. Note that uniq will give you only the unique lines in a file, but it only does so if the duplicated lines are next to each other.

sort my_file.txt | uniq | wc -l

man: See documentation on a command

Get info about how to use a command and the available options with man

man ls

Run a command as the super user

Use sudo followed by the command you want to run. Do this only when absolutely necessary!