This is a glossary of the Linux commands covered in this course.

Notations:

• directory refers to a path to some directory.

• directories refers to a list of one or more directory paths, each path separated by blanks.

• file refers to a path to some file. Directories are files, and so file could be a path to a directory. However, some commands will not work when applied to directories.

  In particular, because directories are binary files, commands that are designed to work on text files will often display an error message if applied to directories.

• files refers to a list of one or more paths to files. Each path is separated from the others by blank spaces.

• new-path is a path to a file that does not exist (yet). All of the directories leading up to the final name in the path must exist.

cd directory

Changes your current working directory to the indicated directory, which may be absolute or relative. Basic File Manipulation

chmod permission files

Set the permissions on a set of files. File Protection

cp

Copies one or more files.

Common variants:

• cp file₁ file₂

  Copies file₁ as file₂. file₂ may be in a different directory. If file₂ already exists, it is replaced by this copy.

• cp file path

  Copies file as path. This variant allows you to copy a file and rename the copy at the same time.

• cp files directory

  Copies all of the listed files , placing the copies in the given directory.

• cp -r files directory

  Copies all of the listed files, …, placing the copies in the given directory. Normally, cp will work only on ordinary files but will ignore any directories in the list of things to be copied. The -r option causes any directories (and their contents) to be copied as well.

find directory instructions

Searches the indicated directory and any subdirectories within it for files. The instructions may serve to limit the files found (e.g., search for files with a given name or that have been modified after a given date) or may indicate commands to run on those files. Commands That Launch Other Commands

ls : Lists the files in directories Basic File Manipulation

Common variations: 

* `ls` _path_

    Lists all the files matching the indicated _path_. If that
    path is a directory, lists all the files within that
    directory. You can provide multiple paths in the same command,
    or omit the path entirely (in which case the contents of your
    current working directory will be listed).

* `ls -a` _path_

    By default, file names beginning with "." are considered
    "hidden" and not shown by the `ls` command. The `-a` (for
    "**a**ll") option causes these files to be shown as well.

* `ls -l` _path_

    This is the "long" form of `ls`. It displays additional
    information about each file, such as the size and date on
    which the file was last modified.


* `ls -F` _path_

    Adds a little bit of extra information to each file name. If
    the file is an executable program, its name is marked with an
    "*". If the file is a directory, its name is marked with "/".


Note that options can be combined. For example,
you can say `ls -la` to get the long extra information
including normally hidden files.

mkdir new-path

Creates a directory. Basic File Manipulation

E.g.,

mkdir ~/newDirectory

would create a newDirectory inside your home directory.

mv

Moves and/or renames files. You must give one or more files to be moved or renamed. If you give one file, you can then supply the path and new file name. If you give multiple files, you cannot rename them but must supply a path to a directory where you want them moved. Basic File Manipulation

Common variants:

• mv file-path₁ file-path₂

  Renames file-path₁ as file-path₂. file₂ may be in a different directory.

  If a the file file-path₂ already exists, and is not a directory, it will be replaced by the moved/renamed file.

• mv file-path directory-path

  Moves file-path, without renaming the file, into the directory directory-path. That directory must already exist, otherwise this is treated as the first variant above.

• mv file-path₁ file-path₂ … directory

  Moves multiple files to the given directory (without renaming them).

pwd

Prints your current working directory. Basic File Manipulation

rm file₁…file_n

Deletes the listed files. Be very careful using wildcards with this command. rm * will delete everything in the current working directory!

rm -i file₁…file_n

Deletes the listed files, but firsts asks permission to delete each one.

rm -r file₁…file_n

Deletes the listed files. If any of these files is a directory, it deletes that directory and everything in it as well.

rmdir directory

Deletes a directory (if empty).

umask number

Sets the default permissions for newly created files. File Protection

cat file₁…file_n

Lists the contents of each of the listed files to stnadard output (by default, your screen). Redirection and Pipes

emacs

Edit a text file, creating an empty one at the given path if it does not already exist. Editing in Text Mode

Common variants:

• emacs -nw file

  Edit in the current window, used mainly in text-mode sessions.

• emacs file &

  Edit in a separate window – used mainly in graphics-mode (X) sessions.

grep regular-expression files

Examines each line of text wihtin the files to see if they match the pattern given as the regular-expression. The matching lines are printed to the output. Wild Cards Typing Unix Commands Searching Lines with grep

Common variations:

• grep -i …

  Upper/lower case is ignored when matching alphabetic characters.

• grep -l …

  Do not list the lines that match the pattern, but list all files contianing at least one matching line.

• grep -v …

  Lists the lines that do not match the pattern.

• If no file paths are given, grep searches through standard input (by default, text typed at the keyboard). This variation is usually combined with redirection or pipes.

more file₁…file_n

Lists files one screen at a time, pausing after each screen-full. Hit the space bar to advance to the next screen. Typing Unix Commands

Hit “b” to go backwards, and “q” to quit. You can search for strings by hitting “/” followed by whatever you want to search for.

A related program is less, which used to do a lot more than more. The original version of more used to be limited to moving forward and quitting, so less was invented to offer more features such as moving backwards and searching. But, over the years, enough of these features have been copied from less into more that now less may not do much more than more, though it certainly does no less.

nano file

Edit a text file, creating an empty one at the given path if it does not already exist. Editing in Text Mode

sed editing-instructions file

Applies the editing instructions to each line of the file, writing out the resulting changed version of the file.

The most common editing instruction is the “substitute” instruction, s/pattern/replacement/, which tells sed to scan each line of the input for text that matches a regular expression pattern and replaces matching text with replacement.
Rewriting lines with sed

Common variations:

• sed s/_pattern_/_replacement_/i file

  Ignores upper/lower case when matching alphabetic characters.

• sed s/_pattern_/_replacement_/g file

  If a single line matches the pattern more than once, replaces all matching text. With the g flag, only the first match in each line is replaced.

• If no file name is given, sed searches through standard input (by default, text typed at the keyboard). This variation is usually combined with redirection or pipes.

vim file

Edit a text file, creating an empty one at the given path if it does not already exist. Editing in Text Mode

Common variants:

• vim -g file &

  Edit in a separate window. You must be in a graphics mode (X) session.

exit

Shut down the current shell. If this shell is the one you got at log-in, this command logs you out. Logging In to Remote Linux Machines

rlogin machine

Logs you in to another machine on the network. Use this if the machine you are on seems to be running slowly and the who command indicates that there are lots of others on the same machine.

who

Lists everyone logged into the same machine that you are using. Logging In to Remote Linux Machines Typing Unix Commands

wc files

Lists the number of characters, words, and lines in a text file. Redirection and Pipes

Common variations:

• wc -l files

  Lists only the number of lines.

• If no file paths are given, wc looks instead at the standard input.

wget URL

Fetches a file for which you have an internet URL, depositing that file in your current directory

scp localFilePath _yourName@machineName:remoteFilePath_

Copies a file from your current machine to a remote one. remoteFilePath must be given as an absolute path.

scp _yourName@machineName:remoteFilePath_ localFilePath

Copies a file from a remote machine to your current one. remoteFilePath must be given as an absolute path.

ssh _yourName@machineName_

Logs in to a remote machine and allows you to issue commands to it. Logging In to Remote Linux Machines

7 Miscellaneous

date

prints the current date and time. Commands That Launch Other Commands

echo parameters

Prints its parameters. Typing Unix Commands

This can be useful as a way of seeing what the command shell does to various special characters before invoking a command. E.g.,

echo I am $USER
echo *

man command

Prints the help (manual) pages for the command. Typing Unix Commands

xargs command

Accepts a list of file paths from standard input and issues the command on each of them. Commands That Launch Other Commands