Learn UNIX in no time !
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
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'.
cd ~bob
Change the current directory to the user bob's home directory (if you
have permission).
Listing directory contents:
ls list a directory
ls -l list a
directory in long ( detailed ) format
for example:
$ ls -l
drwxr-xr-x 4
cliff user 1024 Jun 18 09:40 WAITRON_EARNINGS
-rw-r--r-- 1
cliff user 767392 Jun 6 14:28 scanlib.tar.gz
^ ^ ^ ^
^ ^ ^
^ ^ ^
^
| | | |
| | |
| | |
|
| | | | |
owner group size
date time name
| | | |
number of links to file or directory contents
| | | permissions for world
| | permissions for
members of group
| permissions for owner of file: r = read, w = write, x =
execute -=no permission
type of file: - = normal file, d=directory, l = symbolic
link, and others...
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 using
long
format. 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 newname
move or rename a file
mv file1 ~/AAA/
move file1 into sub-directory AAA in your home directory.
rm file1 [file2 ...]
remove or delete a file
rm -r dir1 [dir2...]
recursivly remove a directory and its contents BE CAREFUL!
mkdir dir1 [dir2...]
create directories
mkdir -p dirpath
create the directory dirpath, including all implied directories in the
path.
rmdir dir1 [dir2...]
remove an empty directory
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:
echo $SHELL
Of course you can create a file with a list of shell
commands and execute it like
a program to perform a task. This is called a shell script.
This is in fact the
primary purpose of most shells, not the interactive command
line behavior.
Environment variables
You can teach your shell to remember things for later using
environment variables.
For example under the bash shell:
export CASROOT=/usr/local/CAS3.0 Defines the variable CASROOT
with the value
/usr/local/CAS3.0.
export LD_LIBRARY_PATH=$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
By prefixing $ to the variable name, you can evaluate it in
any command:
cd $CASROOT
Changes your present working directory to the value of CASROOT
echo $CASROOT
Prints out the value of CASROOT, or /usr/local/CAS3.0
printenv CASROOT
Does the same thing in bash and some other shells.
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 > newfile 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.
du -sc * | sort -n | tail
The
command "du -sc" lists the sizes of all files and directories in the
current
working directory. That is piped through "sort -n" which orders the
output
from smallest to largest size. Finally, that output is piped through
"tail"
which
displays only the last few (which just happen to be the largest) results.
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.gz
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 and apropos commands
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
You can search through the man pages using apropos
Example:
apropos build
Shows a list of all the man pages whose discriptions contain the word
"build"
Do a man apropos for detailed help on apropos.
Basics of the vi
editor
Opening a file
vi filename
Creating text
Edit modes: These keys enter editing modes and type in the
text
of your document.
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 respectivly. Your arrow keys
should also work if
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 (meaning global),
all
instances of string1 on each line
are
substituted. If g is not included,
only the first instance per matching 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 by pressing colon (:) and
then entered in the lower
left corner of the window. They are called "ex"
commands because they are commands
of the ex text editor - the precursor line editor to the
screen editor
vi. You cannot enter
an "ex" command when you are in an edit mode (typing text onto the
screen)
Press <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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