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Generally useful *nix command cheatsheet#

whoami Prints the username with which you logged in

pwd Prints your 'present working directory.'

ls 'Lists' the files in a current directory by itself, or given a path will list the files in that directory.

  • Useful flags:

    • -a: list all files, even 'hidden' files

    • -h: make file sizes human readable (e.g. 4.0K instead of 4000)

    • -l: print in tabular 'list' form

      ls -l /home/brian/a_directory/

      • This would print out a list of the files in this directory, regardless of your present working directory.

cd 'Change directory' from your pwd to some target.

  • If the directory is nested within your pwd you can type a relative path. If it is not, you should type an absolute path.

    cd /home/brian/a_directory

  • Useful shortcuts for directory locations:

    • \~: Your home directory (e.g. /home/USERNAME)

    • ..: The directory above the current one (e.g. if you're in /home/USERNAME, .. refers to /home)

cp Makes a 'copy' of a file and places it in a target directory

  • This would create a new copy with the same name in a new directory:

    cp filename.txt /home/brian/newDirectory/

  • This would create a new copy with a different name in a new directory:

    cp filename.txt /home/brian/newDirectory/differentname.txt

mv 'Move' a file from its current location to a new location.

  • The syntax is similar to cp.

  • This is also a simple way to change the name of a file in its current directory.

    mv filename.txt differentname.txt

rm 'Removes' a file now and forever.

  • Useful flags:

    • -i interactive mode, requires you to confirm each file deletion.

    • r used with a target directory to delete all of its contents as well as the directory itself

rmdir 'Removes a directory' now and forever.

  • The directory must be empty. If you're really sure you want to delete a full directory, use rm -r or perhaps rm -ir as above.

mkdir 'Makes a directory.'

  • Make a directory called 'newDirectory' in my pwd:

    mkdir newDirectory

  • Make a directory called 'newDirectory' in a specified path:

    mkdir /home/brian/specifiedPath/newDirectory/

touch Creates an empty file with the specified name. Sometimes useful.

  • Create a new text file called newFile.txt

    touch newFile.txt

chown Changes the ownership of a file.

  • Change the owner of secretDocument.txt from its current owner to 'brian'

    chown brian secretDocument.txt

chgrp Changes the group ownership of a file.

  • Change the group ownership of secretDocument.txt from its current group to 'trustedGroup'

    chgrp trustedGroup secretDocument.txt

chmod Changes the permissions of a file.

  • There are three sets of permissions for a file: User, Group, and Other. The 'user' is the owner of the file, the 'group' is the group, and 'other' is anyone who is not the owner and not in the group.

  • For each set, there are three permissions: Read, Write, and eXecute.

  • A block of permissions will be printed in three triplets, representing the three permissions for each of the three sets:

    • rwxrw-r-- means that the user can read, write, and execute; the group members can read and write; and anyone else can only read the file.

  • To change permissions of a file, issue chmod with an argument specifying which set of permissions you want to modify, a + to add permissions or a - to remove permissions, and the permissions you want to modify.

    • This will add permissions for the user and group to read and write to secretDocument.txt.

      chmod ug+rw secretDocument.txt

    • This will remove permissions for anyone who is not the user or the group to read or write to secretDocument.txt.

      chmod o-rw secretDocument.txt

cat 'Concatenates' or prints the entire contents of a file to the screen (STDOUT).

  • If you accidentally print out the contents of a gigantic file and want to kill it, you can do so with Ctrl-C.

head Print the first n lines of a file.

  • The default behavior is n=10. This can be modified with the -n flag, as in

    head -n 100 secretDocument.txt

    which would print the first 100 lines of that file.

tail Print the last n lines of a file.

  • The default is n=10. This can also be modified with the -n flag, as above.

  • Additionally, you can use tail to drop the first line of a file, like this:

    tail -n +2 secretDocument.txt

    which can be useful if you want to drop the line containing column headings, for example.

sort Print sorted output.

  • Useful flags;

    • -k Specifies the column number you want to sort by. You can specify multiple columns.

    • -g Specifies that you want to sort using numbers based on scientific notation. This is generally how I sort numbers. There are many other flags for different variable types (alphabetic, date/time, etc).

cut Prints a specified set of input data to the screen.

  • Useful flags:

  • -f Specifies the column numbers you want to display. Separate multiple columns with commas, or type ranges of columns like '1-10'.

Last update: January 11, 2024