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Basic UNIX Command Line (shell) navigation
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http://freeengineer.org/learnUNIXin10minutes.html
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).
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.
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
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.
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 $SHELL
Of
course you can create a file with a list of shell commands and execute it like
a
program to perform a task. This is called a shell script. This is in fact the
primary
purpose of most shells, not the interactive command line behavior.
You
can teach your shell to remember things for later using environment variables.
For
example under the bash shell:
export
CASROOT=/usr/local/CAS3.0
Defines the variable CASROOT with the value
/usr/local/CAS3.0.
export
LD_LIBRARY_PATH=$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.
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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 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 (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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