We will cover the following sections in this article:
- 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 and apropos commands
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Basic UNIX Command Line (shell) navigation
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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
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Moving around the file system:
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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).
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Listing directory contents:
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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
starts 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.
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Changing file permissions and attributes
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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.
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Moving, renaming, and copying files:
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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
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Viewing and editing files:
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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.
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Shells
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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 $SHELL
Of course you can create a file with a list of shell commands and execute it like
a program to perform a task. This is called a shell script. This is in fact the
primary purpose of most shells, not the interactive command line behavior.
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Environment variables
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You can teach your shell to remember things for later using environment variables.
For example under the bash shell:
export CASROOT=/usr/local/CAS3.0 Defines the variable CASROOT with
the value /usr/local/CAS3.0.
export LD_LIBRARY_PATH=$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.
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Interactive History
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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.
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Filename Completion
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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).
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Bash is the way cool shell.
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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.
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Redirection:
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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.
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Pipes:
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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.
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Command Substitution
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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.
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Searching for strings in files: The grep command
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grep <string> <filename> prints all the lines in a file that contain the string
or
cat <filename> |grep <string>
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Searching for files : The find command
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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.
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Reading and writing tapes, backups, and archives: The tar command
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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
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File compression: compress, gzip, and bzip2
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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.
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Looking for help: The man and apropos commands
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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.
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--Regards
V3nom
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