This Linux quick reference has been compiled by current and former members of the EECS IT Support staff as a guide for the most basic Linux commands.
In a Linux shell, there are two types of paths. There are absolute paths (beginning in /) that define a full path from the root directory and relative paths (paths that don't begin with /) that are relative to your current directory. Example:
| Example | Path Description |
foo.c | The relative path to the file foo.c in the current working directory |
pgms/foo.c | The relative path to the file foo.c in the pgms directory within the current working directory |
/home/jruser/pgms/foo.c | The absolute path to the file foo.c based on the root of the file system |
| Abbreviation | Meaning |
~ | Your home (login) directory |
~username | The home directory for the username |
. | The current working directory |
.. | The parent directory of the current one |
../.. | The parent directory of the parent directory |
| Character | Meaning |
? | Match a single character |
* | Match zero or more characters |
Examples
| Expression | Description | Examples |
fo?.c | Matches fo followed by any single character, followed by .c | foa.c, fob.c, foc.c, fo1.c |
foo.* | Matches foo. followed by zero or more characters | foo.txt, foo.exe, foo., foo.png |
| Command | Effect |
command > myfile | Redirects the output of command to the file myfile instead of stdout (the terminal output). If myfile exists, its contents will be replaced. |
command » myfile | Similar to > except that it appends to the end of the file rather than overwriting. |
command < myfile | Redirects the contents of myfile to the input of command rather than stdin (keyboard terminal input). |
cmd1 | cmd2 | Redirects (“pipes”) the output of cmd1 to the input of cmd2. |
command | tee myfile | Duplicates the output of command to both stdout and myfile. |
script myfile | Logs everything displayed on the terminal to the file myfile. The logging is terminated with exit. |
| Command | Effect |
cat > myfile | Allows you to enter text with the keyboard to be stored in the file named myfile. After entering the desired text, press Crtl+D. |
vim myfile | Launches vim text editor on the file myfile |
| Command | Effects |
cat myfile | Displays entire contents of the file myfile at once. Note that to scroll this content, your terminal pragram must be able to handle scrolling. |
less myfile | Displays contents of the file myfile in a full screen, scrollable view. |
| Command | Effect |
diff file1 file2 | Performs a line-by-line comparison of the files file1 and file2. The differences are displayed in the shell output. |
cmp file1 file2 | Performs a byte-by-byte comparison of the files file1 and file2. The differences are displayed in the shell window. |
Compressing files can reduce the size of files and help conserve space.
| Command | Effect |
gzip myfile | Compresses the file myfile, replacing it with the file name myfile.gz |
gunzip myfile.gz | Uncompresses the file myfile.gz, replacing it with the file named myfile |
| Command | Effect |
grep hello myfile | Displays the lines from myfile that contain the string hello |
grep hello file1 file2 | Displays the lines within files file1 and file2 that contain the string hello |
grep “some string with spaces” myfile | Displays the lines within the file myfile that contain the entire string some string with spaces |
grep hello * | Displays the lines within any file in the current directory that contain the string hello (Fun fact: the * is not parsed by grep but instead by the shell. * is a wildcard in the shell that expands to a space delimited list of all files in the current directory) |
grep -v hello * | Displays the lines within any file in the current directory that do not contain the string hello (-v stands for invert-match) |
grep -i hello * | Displays the lines within any file in the current directory that contain the string hello in any letter-case. For example, lines containing hello, HELLO, and HeLlO would all be displayed |
Process and Job Control
Listing Processes and Jobs
| Command | Effect |
ps | Displays a list of processes and corresponding PIDs |
ps gx | Displays a list of processes and corresponding PIDs, including “hidden” processes |
jobs | Displays a list of current jobs and corresponding job-IDs. |
To stop (suspend) a job/process, type CTRL+Z. The suspended process will still be listed in the list of active processes, even though it has been suspended from active execution.
To run a job in the background, the easiest way is to start the process in the background. You can do this by adding a & anywhere after the command.
| Command | Effect |
firefox & | Launches Firefox as a background process. The browser window will still appear; however, your shell will continue to accept commands. |
bg | Continues running the most recently suspended job in the background |
You can also suspend a process running in the foreground by pressing CTRL+Z and move it to the background:
~> firefox
# firefox is now running in the foreground and the terminal is not available
# press CTRL+Z to suspend it and get the shell back
~> bg
~>
| Command | Effect |
fg | Brings the last suspended job to the foreground |
fg id# | Brings the job corresponding to the job-ID id# to the foreground (You can find job IDs by running jobs as mentioned above) |
| Command | Effect |
CTRL+C | Terminates the current program in the foreground, telling it to quickly finish |
kill id# | Terminates the job/process with the job-ID/PID id#, telling it to quickly finish |
kill -KILL id# | Kills the job/process with the job-ID/PID id# (This is a stronger kill than the other two, which should essentially forces it to terminate without giving it time to finish) |
Miscellaneous Commands
Displaying the Current Date and Time
| Command | Effect |
date | Displays the current date and time |
| Command | Effect |
lpstat -p | Lists all available printers and their statuses |
lp myfile | Prints the file myfile on the default printer |
lp -d myprinter myfile | Prints the file myfile on the printer named myprinter |
lp -n # myfile | Prints # copies of the file myfile |
lp -o sides=two-sided myfile | Prints the file myfile double-sided (if the printer supports it) |
lpstat -o myprinter | Displays the contents of the print queue. |
cancel id# | Cancels the print request identified by id number id# |
See Command-Line Printing for more info.
| Command | Effect |
who | Displays a list of the users logged into the current machine |
Using the Command History
| Command | Effect |
history | Displays the last 15 commands from the current session |
!num | Repeats the command with history number num |
!str | Repeats the most recent command that begins with the string str |
!! | Repeats the last command |
!$ | Expands to the last argument of the last command |
grep command $HISTFILE | Searches your history file for the command. history only applies to the current shell session, but the log of all shells is saved to your histfile when you exit |