UNIX Shortcuts and symbols

Shortcut/symbol Description
Ctrl+C Kills current process/command.
tab (tab key) Autocomplete.
↑ (up arrow) Scroll back through previous commands in an interactive shell.
~ (tidle) Represents your home directory.
. Represents the current directory you are in
.. Represents one directory backwards.

For example, the relative path .. refers to “one directory back,” the relative path ../.. refers to “two directories back,” and so on.
* Wildcard symbol.
| Pipe symbol (located on the backslash key). Join a string of UNIX commands together into a “pipeline.”
> and >> Redirect (“send”) output from the command line, for example to a file.

> will overwrite the destination file, and >> will append to the destination file.

UNIX commands

Manipulating files and directories

  • cp: Copy a file or directory.

    • The cp command does not change the original file. It is similar to “copy and paste.”
    # Make a copy of oldfile.txt called newfile.txt
cp oldfile.txt newfile.txt

# Make a copy of the directory directory_original to be called directory_copy
# Copying directories requires the -r flag
cp -r directory_original directory_copy

  • mkdir: Make a new directory

    # Create a new directory called new_directory
mkdir new_directory

# Use the -p flag to avoid errors if the directory already exists
mkdir -p new_directory_that_might_already_have_been_created

# The -p flag also allows you to make nested directories at once
mkdir -p make/all/these/directories/

  • mv: Move or rename a file or directory.

    • The mv command removes the original file. It is similar to “cut and paste.”
    # Rename a file from oldname.txt to newname.txt
mv oldfile.txt newfile.txt

# Move file.txt into a new directory
mv file.txt path/to/new/directory/file.txt

  • rm: Remove a file or directory

    • This is permanent. You cannot recover files deleted with rm
    # Permanently delete a file 
rm file_I_dont_need.txt

# Permanently delete a directory
# Removing directories requires the -r flag
rm -r directory_I_dont_need/

  • touch: Create an new (empty) file

    • When run on existing files, the touch command updates its “last modified by” date (it “touches” the file!)
    # Create a new file
touch name_of_the_new_file_you_want_to_create.txt

# Update modification date of existing file
touch existing_file_to_update_modification.txt

Working with files

  • head (tail): Display the first (last) ten lines of a file

    # See first 10 lines of a file
head file_I_want_to_peek_at.txt

# See last 10 lines of a file
tail file_I_want_to_peek_at.txt

# Use the -n flag to specify a different number of lines, 
#  for example 20:
head -n 20 file_I_want_to_peek_at.txt

  • less: View the contents of a file in the terminal

    • This command was named less named because it is an improved version of the related command more, which also lets you view file contents, and…“less is more.”
    • You can scroll through the view with up and down arrows
    • You can exit the view by typing q
    # View a file's contents 
less file_I_want_to_look_at.txt

  • gunzip: Decompress a .gz-compressed file

    • The gunzip command removes the original file and creates a new file of the same name but without the added extension .gz
    # Decompress very_big_file.txt.gz and create very_big_file.txt
gunzip very_big_file.txt.gz

# Use the -c flag and redirection to retain the original file
gunzip -c very_big_file.txt.gz > very_big_file.txt

  • gzip: Compress a file to .gz format

    • The gzip command removes the original file and a creates a new file of the same name but with the added .gz extension
    # Compress very_big_file.txt and create very_big_file.txt.gz
gzip very_big_file.txt

# Use the -c flag and redirection to retain the original file
gzip -c very_big_file.txt > very_big_file.txt.gz

  • wc: Word count. Count the number of words, lines, characters, and/or bytes in a file

    # Count all values (words, lines, characters, and bytes)
wc file_I_want_to_count.txt

# Only count the number of lines with the -l flag
wc -l file_whose_lines_I_want_to_count.txt

# Only count the number of words with the -w flag
wc -w

Other tasks

  • echo: Print

    # Print a message from a script
echo "Running Step 2"

  • curl: Client URL. Download the contents of a file from a website or server

    • By default, the downloaded file contents get sent to the command line directly (which you almost never want!)
    # Download and save an internet file, using redirection
curl https://database.com/interesting_data.csv > interesting_data.csv

# Use the -o flag to specify the output file, similar to redirection
# The destination filename must directly follow the -o flag
curl https://database.com/interesting_data.csv -o interesting_data.csv

# Use the -O flag to automatically save a file as the same name as it 
#  appears on the internet (here, interesting_data.csv)
curl -O https://database.com/interesting_data.csv

# Use the -s flag to run curl quietly 
# For example, in combination with -O:
curl -sO https://database.com/interesting_data.csv

  • man: See a command’s documentation in the manual

    • Caution: The so-called “man pages” are not always very clear, but they are still often helpful, in particular for seeing different flags you can use with a command
    • You can scroll through the documentation with up and down arrows
    • You can exit the documentation by typing q
    # See the documentation for the echo command
man echo