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
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
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
ctrl+d => Page down
ctrl+u => Page up
:n => Position cursor at line n
:$ => Position cursor at end of file
ctrl+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 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
