Unix/linux 


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







MS-DOS vs. Linux and Unix



If you are able to navigate using MS-DOS, you should be able to quickly pick up on the navigation of Linux and Unix. In the below chart is a listing of common MS-DOS commands with their Linux and Unix counterpart.




MS-DOSLinux and Unix


attribchmod


backuptar


dirls


clsclear


copycp


delrm


deltreerm -R
rmdir


editvi
pico


formatfdformat, mount, and umount


move and renamemv


Typeless <file>


cdcd
chdir


more < filemore file


mdmkdir


winstartx








How to write & compile a C program :-



step 1:



































































































No comments:















Post a Comment
























        

      









Subscribe to:
Posts (Atom)