Basic Unix Commands

The total number of Unix commands is immense. No normal user or system administrator would ever need to know them all.

The Unix commands available to you will vary based upon several factors:

The version of Unix you are using (FreeBSD, Linux, Solaris, AIX, HP-UX, OpenBSD, etc…)
The Unix shell you are using (sh, csh, tcsh, ksh, bash, etc…)
The packages installed on the system and the way the system is configured
Your access level on the system

This list of basic Unix commands will get you started using and learning Unix.

Chart of Basic Unix Commands

Unix Command	Description
ls	List directory contents
cp	Copy files
rm	Remove directory entries
file	Determine file type
find	Walk a file hierarchy
which	Locate a program file in the user’s path
whereis	Locate programs
gcc, g++	GNU project C and C++ Compiler
gdb	The GNU Debugger
less	View the contents of a text file
diff	Find differences between two files
cmp	Compare two files
vi	Text editor
chmod	Change file modes
man	Display the on-line manual pages
mv	Move and rename files
ispell	Interactive spelling checker
biff	Be notified if mail arrives and who it is from
lpr	Print a file
lpq	Show the print queue
ftp	Transfer a file to another Unix system
logout	Quit using the system
pwd	Print working directory name
cd	Change working directory
ln	Make a file link
mkdir	Make directories
rmdir	Remove directories
chmod	Change file modes
quota	Display disk usage and limits
history	Display a list of recent commands
ps	Show the status of processes
kill	Stop a running processes
passwd	Change your password
alias	Create a command alias
unalias	Delete a command alias
export	Set an environment variable
script	Record your terminal session to a file
bg	Send a job to the background
fg	Bring a job to the foreground
jobs	Print a list of current jobs

The basic Unix commands are fairly standard across the various Unix platforms, although command arguments differ at times. In addition, the basic Unix commands vary between Unix shells.

Use the Unix `man` command to learn more about any of these commands.

Basic Unix Commands in Detail

mkdir

Create the DIRECTORY(ies), if they do not already exist.

Usage

mkdir [OPTION] DIRECTORY

Options

Note: Mandatory arguments to long options are mandatory for short options too.

-m, mode=MODE set permission mode (as in chmod), not rwxrwxrwx – umask

-p, parents no error if existing, make parent directories as needed

-v, verbose print a message for each created directory

-help, display this help and exit

-version, output version information and exit

Examples

Create single directory

>mkdir tmp

Create 3 directories

>mkdir memos letters e-mail

Use cd to change directories. Type cd followed by the name of a directory to access that directory.Keep in mind that you are always in a directory and can navigate to directories hierarchically above or below.

Usage

cd DIRECTORYNAME

Example

>cd /home/rich/www

To change the name of a directory. Type mv followed by the current name of a directory and the new name of the directory.

Usage and Example

>mv junk precious

This renames the filejunkas the fileprecious.

pwd

print working directory; will show you the full path to the directory you are currently in. This is very handy to use, especially when you need to perform other directory related tasks.

Usage

pwd

Example:

> pwd
/home
> cd /home/rich/www
> pwd
/home/rich/www
>

rmdir

Remove an existing directory

Usage

rm DIRECTORYNAME

Options

rm -r

Removes directories and files within the directories recursively.

Example

To delete a directory named usersmith, type the following command ((from any directory except usersmith):

>rmdir usersmith

chown

change file owner and group; Change the owner and/or group of each FILE to OWNER and/or GROUP. With –reference, change the owner and group of each FILE to those of RFILE

Usage

chown [OPTION] OWNER[:[GROUP]] FILE

chown [OPTION] :GROUP FILE

chown [OPTION] –reference=RFILE FILE

Options

-c, changes like verbose but report only when a change is made

-dereference affect the referent of each symbolic link, rather than the symbolic link itself

-h, no-dereference affect each symbolic link instead of any referenced file (useful only on systems that can change the ownership of a symlink)

-from=CURRENT_OWNER:CURRENT_GROUP

change the owner and/or group of each file only if its current owner and/or group match those specified here. Either may be omitted, in which case a match is not required for the omitted attribute.

-no-preserve-root do not treat `/’ specially (the default)

-preserve-root fail to operate recursively on `/’

-f, -silent, -quiet suppress most error messages

-reference=RFILE use RFILE’s owner and group rather than the specifying OWNER:GROUP values

-R, -recursive operate on files and directories recursively

-v, -verbose output a diagnostic for every file processed

The following options modify how a hierarchy is traversed when the -R option is also specified. If more than one is specified, only the final one takes effect.

-H if a command line argument is a symbolic link to a directory, traverse it

-L traverse every symbolic link to a directory encountered

-P do not traverse any symbolic links (default)

Examples

>chown hiox test.txt

The owner of the ‘test.txt’ file is root, Change to new user hiox.

chmod

change file access permissions

Usage

chmod [-r] permissions filenames

r Change the permission on files that are in the subdirectories of the directory that you are currently in.

permission Specifies the rights that are being granted. Given below are the different rights that you can grant in an alphanumeric format.

u – User who owns the file.

g – Group that owns the file.

o – Other.

a – All.

r – Read the file.

w – Write or edit the file.

x – Execute or run the file as a program.

Numeric Permissions:

CHMOD can also to attributed by using Numeric Permissions:

400 read by owner

040 read by group

004 read by anybody (other)

200 write by owner

020 write by group

002 write by anybody

100 execute by owner

010 execute by group

001 execute by anybody

Examples

 >chmod u=rwx,g=rx,o=rx filename.cgi

gives:

read, execute, and write access to the user (that’s you)

read and execute access to the group and

read and execute access to others

The same can be achieved by using the command

>chmod 775 filename.cgi

Short listing of directory contents

Usage

ls [OPTION]

Options

-a list hidden files

-d list the name of the current directory

-F show directories with a trailing ‘/’

executable files with a trailing ‘*’

-g show group ownership of file in long listing

-i print the inode number of each file

-l long listing giving details about files and directories

-R list all subdirectories encountered

-t sort by time modified instead of name

Example

To list the contents of the current directory:

>ls

To copy files

Usage and Examples

>cp myfile yourfile

Copy the files “myfile” to the file “yourfile” in the current working directory. This command will create the file “yourfile” if it doesn’t exist. It will normally overwrite it without warning if it exists.

>cp -i myfile yourfile

With the “-i” option, if the file “yourfile” exists, you will be prompted before it is overwritten.

>cp -i /data/myfile

Copy the file “/data/myfile” to the current working directory and name it “myfile”. Prompt before overwriting the file.

>cp -dpr srcdir destdir

Copy all files from the directory “srcdir” to the directory “destdir” preserving links (-doption), file attributes (-p option), and copy recursively (-r option). With these options, a directory and all it contents can be copied to another directory.

Creates a symbolic link to a file.

Usage and Example