unix basics - home - oakton community dos unix command description • cd pwd display current...
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UNIX Basics
UNIX Basics
CIS 218
Oakton Community College
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History
• UNIX was invented in 1969 at AT&T Bell Labs
• Ken Thompson and Dennis Ritchie are credited as the original architects and developers of “C”.
• Written in the C programming language in 1973
• Resold under UNIX System License (USL)
• Current USL version SystemV R4
• Different commercial flavors: Solaris (Sun), AIX (IBM), Irix (SGI), HPUX (Hewlett Packard), SCO
• Academic version – BSD (Mac OS X base)
• UNIX Variants – LINUX,
• UNIX “ports” – Android, MAC OSX
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Unix Design
• Modularity
– Each part of the Unix system is a system unto itself
• printing, networking, mail, file management,
accounting, etc.
– Many Unix systems can be run in different modes. This
allow for a certain set of modules to be run based on usage
(workstation, server).
– UNIX utilities are independently developed packages
UNIX Design
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UNIX Layers
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• UNIX – everything is a file
• UNIX is case sensitive, DOS is not
• UNIX searches $PATH for executables, DOS starts
in current directory, then PATH.
• UNIX is multi-user, DOS is not. Windows is (kind
of)
• UNIX GUI sits “on top of” the OS - same as
Windows thru ME). This changed After NT.
• UNIX directory has one starting point – root “/”.
Windows has multiple A:, C:, D: etc.
UNIX Versus DOS/Windows
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• DOS UNIX Command Description
• CD pwd Display current directory
• CD \ cd / Moves to the root directory
• CD .. cd .. Moves up one level in the directory structure
• CD path cd path Sets the current directory to a new directory
• CHKDSK du Displays disk usage
• CLS clear Clear the screen
• COMMAND sh, csh .. Start a new shell (command processor)
• COMP cmp Compares two files and shows the difference
• COPY cp Copy a file
• DATE date Displays the date
• DEL or ERASE rm Deletes a file
• DELTREE rm -r Deletes a directory tree ( CAREFUL ! ! ! )
• DIR ls -l Lists the directory in a long format
• DIR /W ls Lists the directory in a short format
• ECHO echo Displays a message or a variable
• EXIT exit End a shell
• FC diff Displays differences between two files
• FIND grep Displays lines matching a given pattern
• HELP man Display information about a command
• MD or MKDIR mkdir Creates a directory
• MORE more Displays text a page at a time
• MOVE mv Moves a file
• PRINT lpr Prints a file
• RD or RMDIR rmdir Removes a directory
• REN mv Renames a file
• SET set Sets a variable to a given value
• SORT sort Sorts a data
• TIME date Displays the time
• TYPE cat Displays a file
UNIX Versus DOS/Windows
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Shells
• Shell – “sh” original interface to UNIX
• Bourne Shell added some desirable features but has different syntax for some things
• Newer Bourne Shell variants are Korn Shell (ksh) and Born Again Shell (bash)
• C Shell – C program language syntax, tcsh,
• Perl – Program Extract and Reporting Language
• Some systems allow user to chose which shell you prefer with “chsh”. The full path to the shell must be given
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The Shell
• When you log in to interact with UNIX, you see a
“shell prompt” ($ or %)
• A “word” is a text string separated by white
space – space, Tab or IFS
• The shell is a program that runs constantly and
executes the commands you give it
• A command is the first “word” on a line. All
following words are command line parameters
• Commands terminators: “<LF>” – Enter or
Return, “;”, “|”, “>”
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• You interact with the Unix by entering commands
thru thee shell. The line is parsed as text sepaated by
whitspace caracters into words or tokens. The first
word is always a command.
• The basic form of any Unix command is:
Command Option(s) Argument(s)
• Most commands provide integral help or on-line
Manual (man page)
• Options or flags modify the way that a command
works. They usually consist of a hyphen followed by
a single letter.
UNIX command line
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• d: Directory - holds other files or directories.
• -: Normal Files Text files - text that is “human readable”.
Binary files - executable files
• l: Link - allows space efficient copying of files/directories.
Symbolic or “soft” - may span file systems.
Hard - is indistinguishable from the original file/directory.
• .: Hidden File - any file that begins with a “.” (dot).
• c,b: Character or Block Special Files – hardware
interface.
• “virtual” files – pipes, semaphores, sockets.
Unix file types (ls –l)
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Files and Directories
• UNIX uses a single hierarchy to store files
beginning with root “/”
• Files are a named collection of bytes
• Directories contain other files (or not)
File1
juliana
Project
File2 File3
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Basic Directory Terms • Home directory (~ ) - top of your file tree:
• Root directory (/ ) - top of a file tree:
• Current directory (.) - directory you’re in now (pwd)
• Dot (.) - current directory
• Dot-dot (..) - parent of current directory
• Path - Where to find file or directory
– Absolute path: /fs/scd/home0/juliana/myfile
– Relative path: ./myfile
• “Standard files” – STDIN, STDOUT, STDERR
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Managing Files and Directories
• cd - change directories (built into shell)
• pwd – present working directory
• mkdir - creates a directory
• rmdir - removes a directory (must be empty first)
• rm myfile1 - remove a file
• rm -fr - removes directory and everything below
• touch <filename> - creates an empty file
• cat <filename> - displays a file on screen
• more <filename> - to see a screenful at a time
• mv myfile1 myfile2 - renames (moveas) a file
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Tar and Compress - Tar stands for “tape archive” but is more often used to gather
files into one bundle. Equivalent of a ZIP file, without the compression.
- cd to the directory above the one you want to archive
tar cvf - diry_name > diry.tar
- To “list” the archive, use
tar -xvf diry.tar
- To “untar” the archive, use
tar -xvf diry.tar
- Compressed files take up less space. To compress a tar file, use
compress diry.tar or gzip diry.tar
- To uncompress, use
uncompress diry.tar.Z or gunzip diry.tar.gz
- Note equivalent gzip commands: zcat, zgrep, zmore, zdiff
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File Permissions
• You “own” your files and directories
• user-group-other read/write/execute permissions • -rw-r--r-- 1 jsmith staff 164870 27 Feb 17:58 6.bmp
• -rw-r--r-- 1 jsmith staff 164870 27 Feb 17:57 5.bmp
• + to add, - to remove alphabetic permissions
• r=4, w=2, x=1 so rwx: 4+2+1=7 for numeric
• chmod command changes permissions
chmod 604 6.bmp
chmod g-rw 6.bmp -rw----r-- 1 jsmith staff 164870 27 Feb 17:58 6.bmp
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• Access rights on files.
r : indicates read permission (or otherwise), that is, the presence or absence
of permission to read and copy the file
w : indicates write permission (or otherwise), that is, the permission (or
otherwise) to change a file
x : indicates execution permission (or otherwise), that is, the permission to
execute a file, where appropriate
• Access rights on directories.
r : allows users to list files in the directory;
w : allows users to delete files from the directory or move files into it;
x : allows users the right to access files in the directory (e.g. cd into
directory), read files in the directory provided you have read permission on
the individual files.
File Permissions
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Symbol Meaning
u user
g group
o other
a all
r read
w write (and delete)
x execute (and access directory)
+ add permission
- take away permission
File Permissions
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User Commands for Files
What’s in my directory?
• ls db5-24 nwade.txt schumacher5-19.txt
kirsh5-12.txt nwade5-13a.txt sheu5-20.txt
• ls -alt -rw-r--r-- 1 jsmith staff 712 24 May 09:12 db5-24
-rw-r--r-- 1 jsmith staff 1660 12 May 12:12 kirsh5-12.txt
-rw-r--r-- 1 jsmith staff 3610 11 May 08:16 ming.txt
-rw-r--r-- 1 jsmith staff 2444 10 May 16:53 mingrep
• Wildcard - * stands for any (# of) character(s)
• Wildcard - ? stands for any single character
• [abcde…] selection set, any single character within the brackets
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• wc - word, line, character, and byte count
• echo - echo characters back (print)
• sort - sort lines of a text file
• uniq – remove consecutive duplicats lines
• cut/paste/join – manipulate data by physical location in a record or file
• sed – stream editor, vi commands in a batch file
• awk – string manipulation
• tr – translate from one character to another
• strings – review a binary file for text
• od – examine a file for binary contents
• head, tail – display begin and end of a file
• cat – copy to stdout
• cp – copy a file
User Commands for Files
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Finding and Searching • diff – find differences between two text files
• find - a tricky but useful command
find . -name myfile -print
find . -name ‘*name*’ –print –exec “cmd” {} \;
• grep - stands for “general regular expression print” Search all files for a pattern:
grep -i “lightning system” *
grep -v “lightning system” *
grep -c “gee whiz” *
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• Wildcard characters can be used to represent many other
characters in listing filenames. – Use them whenever you need to define a string of characters, such as a
filename, for use with a command.
– Useful wildcards are:
* matches any characters, zero or more.
? match any single character.
[...] matches any character in the enclosed list or range.
Examples:
– ls *.txt # Lists all the files in the current directory
# that have the extension .txt.
– cat memo? # Concatenate files that start with “memo”
# and are followed by any one character.
– rm part[1-3] # Remove files: part1, part2 and part3
Wildcard characters
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Input/Output (I/O) and Redirection
• By default, a terminal keyboard is the standard input file (STDIN) from which to read in information
• Terminal is also the standard output file (STDOUT) to which information is sent from the command.
• Input can be given from the command line, or from a file: a.out < inputfile
• Output goes to your screen, or you can “redirect” it to a file: echo “hi there” > out.file
• To append, use >>
echo “hi back at you” >> out.file
• “here” document for inline stdin << EOF
• Use the “tee filename” command to redirect out put to both STDOUT and a file.
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• “<& m” Duplicates standard input from file descriptor
m
• “[n] >& m” Duplicates standard output or file
descriptor n if specified from file descriptor m i.e. 2>&1
• “[n] <&-” Closes standard input or file descriptor n if
specified
• “[n] >&-” Closes standard output or file descriptor n if
specified.
• “|” or pipe (prior slide) is also redirection. It redirects
STDOUT from the preceding command to STDIN of
the following command. The general term for the
following command is called a filter as it modifies or
filters the output of the preceding command..
Input/Output (I/O) and Redirection
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Pipes
• You can string commands together into a single
command using pipes ( | )
ps | grep juliana - what am I running now
• Save the results in a file:
“who | wc > usercount”
• Used with file manipulation commands as “filters”
“who | wc” - count how many users on the system
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System Info Commands
• System Uptime
uptime
• What time is it?
date
• Where is a command?
which ls
whereis ls
• How do I use a command?
man ls
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System Info Commands
• Where am I?
pwd - print working directory
cwd - current working directory
• Who am I?
whoami
• Who is on the system? What’s running?
who, w
ps –ef, -aux
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More Useful Commands, cont.
• passwd - change password
• chsh – change default shell
• lpr - print a file (printer at OCC)
• history - (C shell builtin) - list of previous commands
• alias - create a pseudonym or shorthand for a command (behaves differently for C versus Bourne shell)
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Editing - vi
• Front end to ed
• Universal among UNIX and it’s variants
• vi somefilename (copies file into memory
buffer)
• Three modes – command mode, text
mode(Esc), operator line(:) determines
how keystrokes are interpreted by vi
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• i – insert text
• x – delete a character
• r – replace a character
• R – replace text
• yy p – copy a line
• dd – delete a line
• /text – locate text
• / - repeat last find
• <Enter> or <Return> - ends a line
• :wq – save results and quit (:wq! – force overwrite of file)
• :q - quit (no save)
• Navigation: arrow keys or HJKL
Editing – vi (commands)