Unix in 10 minutes

Sections:

Directories

Moving around the file system

Listing directory contents

Changing file permissions and attributes

Moving, renaming, and copying files

Viewing and editing files

Shells

Environment variables

Interactive History

Filename Completion

Bash is the way cool shell

Redirection

Pipes

Command Substitution

Searching for strings in files: The grep  command

Searching for files: The find command

Reading and writing tapes, backups, and archives: The tar command

File compression: compress, gzip, and bzip2

Looking for help: The man command

Basics of the  vi editor

Basic UNIX Command Line (shell) navigation

Last revised May 17 2001

Directories

File and directory paths in UNIX use the forward slash “/”

to separate directory names in a path.

examples:

/

“root” directory

/usr

directory usr (sub-directory of / “root” directory)

/usr/STRIM100

STRIM100 is a subdirectory of /usr

<new>

Moving around the file system

Pwd

Show the “present working directory”, or current directory.

Cd

Change current directory to your HOME directory.

cd /usr/STRIM100

Change current directory to /usr/STRIM100.

cd INIT

Change current directory to INIT which is a sub-directory of the current directory.

cd ..

Change current directory to the parent directory of the current directory.

cd $STRMWORK

Change current directory to the directory defined by the environment variable ‘STRMWORK’.

Listing directory contents

ls

list a directory

ls -l

list a directory in long ( detailed ) format

For example:

$ ls -l

-rw-r–r–    1 cliff  user ~

|  |     |       |   |       |

A B C D    E  F     G

** this is split over 2 lines **

~ 76739 Jun 6 14:28 scan.tar

|          |         |          |

H         I        J         K

A – Type: – = Normal

d = Directory

l = Symbolic link

Others exist.

B – Permissions for owner

C – Permissions for group

D – Permissions for world

E – Number of links

F – Owner

G – Group

H – Size

I – Date

J – Time

K – Name of file

ls -a

List the current directory including hidden files. Hidden files start with “.”

ls -ld *

List all the file and directory names in the current directory.  Without the “d” option, ls would list the contents of any sub-directory of the current. With the “d” option, ls just lists them like regular files.

Changing file permissions and attributes

chmod 755 file

Changes the permissions of file to be rwx for the owner, and rx for  the group and the world. (7 = rwx = 111 binary. 5 = r-x = 101 binary)

chgrp user file

Makes file belong to the group user.

chown cliff file

Makes cliff the owner of file.

chown -R cliff dir

Makes cliff the owner of dir and everything in its directory tree.

You must be the owner of the file/directory or be root before you can do any of these things.

Moving, renaming, and copying files

cp file1 file2

copy a file

mv file1 renamed file1

move or rename a file

rm file1 [file2 …]

remove or delete a file

rm -r dir1 [dir2…]

recursivly remove a directory and its contents BE CAREFUL!

mkdir dir1 [dir2…]

make a directory

rmdir dir1 [dir2…]

remove an empty directory

<new>

Viewing and editing files

cat filename

Dump a file to the screen in ascii.

more filename

Progressively dump a file to the screen: ENTER = one line down SPACEBAR = page down  q=quit

less filename

Like more, but you can use Page-Up too. Not on all systems.

vi filename

Edit a file using the vi editor. All UNIX systems will have vi in some form.

emacs filename

Edit a file using the emacs editor. Not all systems will have emacs.

head filename

Show the first few lines of a file.

head -n  filename

Show the first n lines of a file.

tail filename

Show the last few lines of a file.

tail -n filename

Show the last n lines of a file.

Shells

The behavior of the command line interface will differ slightly depending

on the shell program that is being used.  Depending on the shell used, some extra behaviors can be quite nifty.  You can find out what shell you are using by the command:

printenv SHELL

Of course you can create a file with a list of shell commands and execute it like a program to perform a task. This is called a shell script. This is in fact the primary purpose of most shells, not the interactive command line behavior.

Environment variables

You can teach your shell to remember things for later using environment variables.

For example under bash:

export CASROOT=/usr/local/CAS3.0

Defines the variable CASROOT with the value /usr/local/CAS3.0.

cd $CASROOT

Changes your present working directory to the value of CASROOT

export LD_LIBRARY_PATH=$CASROOT/Linux/lib

Defines the variable LD_LIBRARY_PATH with the value of CASROOT with /Linux/lib appended, or /usr/local/CAS3.0/Linux/lib

printenv CASROOT

Will print out the value of CASROOT, or /usr/local/CAS3.0

echo $CASROOT

Does exactly the same thing

env | grep CASROOT

A roundabout way to get the same information.

Interactive History

A feature of bash and tcsh (and sometimes others) you can use the up-arrow keys to access your previous commands, edit them, and re-execute them.

Filename Completion

A feature of bash and tcsh (and possibly others) you can use the TAB key to complete a partially typed filename. For example if you have a file called constantine-monks-and-willy-wonka.txt in your directory and want to edit it you can type ‘vi const’, hit the TAB key, and the shell will fill in the rest of the name for you (provided the completion is unique).

Bash is the way cool shell.

Bash will even complete the name of commands and environment variables.And if there are multiple completions, if you hit TAB twice bash will show you all the completions. Bash is the default user shell for most Linux systems.

Redirection:

grep string filename >

Redirects the output of the above grep command to a file ‘newfile’.

grep string filename >> existfile

Appends the output of the grep command to the end of ‘existfile’.

The redirection directives, > and >> can be used on the output of most commands to direct their output to a file.

Pipes

The pipe symbol “|” is used to direct the output of one command to the input

of another.

For example:

ls -l | more

This commands takes the output of the long format directory list command “ls -l” and pipes it through the more command (also known as a filter).  In this case a very long list of files can be viewed a page at a time.

Command Substitution

You can use the output of one command as an input to another command in another way called command substitution. Command substitution is invoked when by enclosing the substituted command in backwards single quotes. For example:

cat `find . -name aaa.txt`

which will cat ( dump to the screen ) all the files named aaa.txt that exist in the current directory or in any subdirectory tree.

Searching for strings in files: The grep command

grep string filename

prints all the lines in a file that contain the string

Searching for files : The find command

find search_path -name filename

find . -name aaa.txt

Finds all the files named aaa.txt in the current directory or any subdirectory tree.

find / -name vimrc

Find all the files named ‘vimrc’ anywhere on the system.

find /usr/local/games -name “*xpilot*”

Find all files whose names contain the string ‘xpilot’ which exist within the ‘/usr/local/games’ directory tree.

Reading and writing tapes, backups, and archives: The tar command

The tar command stands for “tape archive”. It is the “standard” way to read

and write archives (collections of files and whole directory trees).

Often you will find archives of stuff with names like stuff.tar, or stuff.tar.gz.  This is stuff in a tar archive, and stuff in a tar archive which has been compressed using the gzip compression program respectivly.  Chances are that if someone gives you a tape written on a UNIX system, it will be in tar format, and you will use tar (and your tape drive) to read it.  Likewise, if you want to write a tape to give to someone else, you should probably use

tar as well.

Tar examples:

tar xv

Extracts (x) files from the default tape drive while listing (v = verbose) the file names to the screen.

tar tv

Lists the files from the default tape device without extracting them.

tar cv file1 file2

Write files ‘file1’ and ‘file2’ to the default tape device.

tar cvf archive.tar file1 [file2…]

Create a tar archive as a file “archive.tar” containing file1, file2…etc.

tar xvf archive.tar

Extract from the archive file

tar cvfz archive.tar.gz dname

Create a gzip compressed tar archive containing everything in the directory ‘dname’. This does not work with all versions of tar.

tar xvfz archive.tar.

Extract a gzip compressed tar archive.  Does not work with all versions of tar.

tar cvfI archive.tar.bz2 dname

Create a bz2 compressed tar archive. Does not work with all versions of tar

File compression: compress, gzip, and bzip2

The standard UNIX compression commands are compress and uncompress. Compressed files have a suffix .Z added to their name. For example:

compress part.igs

Creates a compressed file part.igs.Z

uncompress part.igs

Uncompresseis part.igs from the compressed file part.igs.Z.  Note the .Z is not required.

Another common compression utility is gzip (and gunzip). These are the GNU compress and uncompress utilities.  gzip usually gives better compression than standard compress, but may not be installed on all systems.  The suffix for gzipped files is .gz

gzip part.igs

Creates a compressed file part.igs.gz

gunzip part.igs

Extracts the original file from part.igs.gz

The bzip2 utility has (in general) even better compression than gzip, but at the cost of longer times to compress and uncompress the files. It is not as common a utility as gzip, but is becoming more generally available.

bzip2 part.igs

Create a compressed Iges file part.igs.bz2

bunzip2 part.igs.bz2

Uncompress the compressed iges file.

Looking for help: The man command

Most of the commands have a manual page which give sometimes useful, often more or less detailed, sometimes cryptic and unfathomable discriptions of their usage. Some say they are called man pages because they are only for real men.

Example:

man ls

Shows the manual page for the ls command

Basics of the vi editor

Opening a file

vi filename

Creating text

i     Insert before current cursor position

I     Insert at beginning of current line

a    Insert (append) after current cursor position

A    Append to end of line

r     Replace 1 character

R    Replace mode

<ESC> Terminate insertion or overwrite mode

Deletion of text

x      Delete single character

dd    Delete current line and put in buffer

ndd  Delete n lines (n is a number) and put them in buffer

J      Attaches the next line to the end of the current line (deletes carriage return).

Oops

u     Undo last command

Cut and paste

yy    Yank current line into buffer

nyy  Yank n lines into buffer

p      Put the contents of the buffer after the current line

P      Put the contents of the buffer before the current line

Cursor positioning

^d    Page down

^u    Page up

:n     Position cursor at line n

:$     Position cursor at end of file

^g    Display current line number

h,j,k,l Left,Down,Up, and Right respectively.

Your arrow keys should also work if your keyboard mappings are anywhere near sane.

String  substitution

:n1,n2:s/string1/string2/[g]

Substitute string2 for string1 on lines n1 to n2. If g is included (global),  all instances of string1 on each line are substituted. If g is not included, only the first instance per line is substituted.

^ matches start of line

. matches any single character

$ matches end of line

These and other “special characters” (like the forward slash) can be “escaped” with \

i.e to match the string “/usr/STRIM100/SOFT” say “\/usr\/STRIM100\/SOFT”

Examples:

:1,$:s/dog/cat/g

Substitute ‘cat’ for ‘dog’, every instance for the entire file – lines 1 to $ (end of file)

:23,25:/frog/bird/

Substitute ‘bird’ for ‘frog’ on lines 23 through 25. Only the first instance on each line is substituted.

Saving and quitting and other ex commands

These commands are all prefixed bu touching the colon (:) and entered in the lower left corner of the window. You cannot enter a ex command when you are in an edit mode. Touch <ESC> to exit from an editing mode.

:w

Write the current file.

:w new.file

Write the file to the name ‘new.file’.

:w! existing.file

Overwrite an existing file with the file currently being edited.

:wq

Write the file and quit.

:q

Quit.

:q!

Quit with no changes.

:e filename

Open the file ‘filename’ for editing.

:set number

Turns on line numbering

:set nonumber

Turns off line numbering

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