Quick UNIX Tutorial
description
Transcript of Quick UNIX Tutorial
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Quick UNIX Tutorial
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Outline
• Getting help while on the system• The shell• Working with files & directories• Wild card characters• Security• I/O redirection• pipes• process and job control commands
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Logging in the first time
• Change your passwordpasswd
• To logout logout or exit
Note: all Unix commands are case sensitive
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Getting Help from the System• All Unix commands are described online in a
collection of files called “man pages”man command
• For help on some topicman -k keyword
• For more information on using the man pagesman man
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General command format
Command -options arguments
• options/flags generally identify some optional capabilities
• some parts of a command are optional. These are indicated in the man pages with [ ]
• case sensitive
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The shell• The Unix process that interprets your commands is called
the “shell”• When you login, the login process, after it verifies the
user’s username and password, creates a shell process.• The shell process displays a prompt on the screen and
waits. • When the user enters a command, the shell examines it,
interprets it and either executes it or calls another program to do so.
• After the command is executed, the shell displays the command prompt and waits again.
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The shell
• There are several Unix shells• The Bourne shell(sh) and the C shell(csh) are the
most popular. The TC shell (tcsh) is variation of the C shell. Bourne Again Shell (bash) is the default on gator
• To display the shell you’re usingecho$SHELL--> /bin/tcsh
• To change to another shellchsh
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Files and Directories• Home directory:
– The actual path of your home directory may be something like: /home/student/username
– Note the forward slashes
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Listing contents of a directory
Ls (list files and directories) ls
– The ls command lists the contents of your current working directory.
• > ls Mail courses jets.com News cs4315
g.cc junk proj3 vhdl adsrc ddm ga mail public_html bin exam2.cc misc resch
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Listing contents of a directory To generate a detailed listing
ls -l• to display type of file
ls -F• May combine flags
ls -lF To generate listing of a specific directoryls -lF pathnamewhere pathname is the path of intended directory.
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Aliases
alias dir = 'ls -lF'
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Configuration Files• ls lists all files except those starting with a dot: "."• Generally, files that start with a dot are supposed to
be program configuration files• to list all files and directories in current directory,
including hidden files ls -a
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.files• In your home directory there are two hidden files “.login” and ".cshrc"..login: login configuration file.bash_profile: the bash initialization file
• In every directory there are “.” and “..”
“.”: points to the current working directory“..”: points to the parent directory of the
current working directory.
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Wildcards• The characters * will match against one or more
characters in a file or directory name. ls proj*
• The character ? Will match against any single character
• [ ]: the brackets enclose a set of characters any one of which may match a single character in that position.e.g cat proj[125]cat proj[1-7]
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Wildcards• ~: a tilde at the beginning of a word expands to
the name of your home directory.e.g: ls ~
cat ~/proj1.cc• if you append ~ to a user name, it refers to that
user’s home directory.
e.g: ls ~smithlists all files in home directory of user smith
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Making Directories
mkdir (make directory)mkdir name
• creates a subdirectory in current working directory
mkdir somepath/name
• creates a subdirectory in directory somepath
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Changing to a different directorycd (change directory)
cd pathname• change current working directory to pathname.
• cd by itself will make your home directory the current working directory
• cd ..: cd to parent of current directory• cd ~ : cd to home directory
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Pathnames • pwd (print working directory)
> pwd/home/student/smith
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Copying filescp (copy)
cp file1 file2• makes a copy of file1 and calls it file2. File1 and
file2 are both in current working directory.
cp pathname1/file1 pathname2• copies file1 to pathname2e.g cp ~/tutorial/science.txt .
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Moving files
mv (move)mv file1 file2
• moves (or renames) file1 to file2• use the -i option to prevent an existing file from
being destroyed mv -i file1 file2
• if file2 already exist, mv will ask if you really want to overwrite it.
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Removing files and directories
rm (remove)rm file1 [file2]…
• Use the -i option for interactive remove:
rm -i proj*.*
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Removing files and directories
rmdir (remove directory)rmdir path
• will not remove your current working directory• will not remove a directory that is not empty• To remove a directory and any files and
subdirectories it contains use -r (recursively)
rmdir -r pathrmdir -ir path
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Displaying the contents of a file on the screen
cat (concatenate)cat myfile
displays the contents of myfile on monitorcat file1 file2 file3
more displays a file on the screen one page at a time. Use space
bar to display to next page.Head -- displays first 10 linestail -- displays last 10 lines
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Searching the contents of a file• Searching using moreFor example, to search myfile for the word
science, type more myfile
then type / science
Type n to search for the next occurrence of the word
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Searching the contents of a file• Searching using grep> grep music myfile • To ignore upper/lower case distinctions, use the -i
option> grep -i music myfile • To search for a phrase or pattern, you must
enclose it in single quotes. For example to search for the phrase operating systems, type
> grep -i 'operating systems' myfile
> grep -i 'operating systems' *
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Searching the contents of a file
Some of the other options of grep are: -v display those lines that do NOT match
-n precede each matching line with the line number
-c print only the total count of matched lines
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Other Useful Commands
wc (word count)• To do a word count on myfile, type wc -w myfile
• To find out how many lines the file has, type wc -l myfile
• To do bothwc myfile
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Other Useful Commands• wholists on the screen all the users currently logged to
the system• finger usernamelists information about a user• sort takes it is input from the standard input (keyboard)
and sorts the lines in alphabetical order.
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Redirecting Input and Output• In general, Unix commands use the standard input
(keyboard) and output (screen).• < : redirect input• > and >> : redirect outputExample:
who > namelistwho >> namelistsort < namelistsort < namelist > newnamelistsort < namelist > namelist
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Redirecting Input and Output• Another example: search for the word mysort in
all the c source files in the current directory and write the output to file1.
• grep mysort *.c > file1
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Using redirection to concatenate files
• Examples:cat file1 > file2
copies file1 into file2
• To concatenate files:cat file1 file2 > file3
• orcat file2 >> file1
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Pipes• A pipe is a way to use the output from one
command as the input to another command without having to create intermediary files.
• Example: want to see who is logged in, and you want the result displayed alphabetically:
who > namelistsort namelist
• Using a pipe:who | sort
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Pipes• Example: want to get a count of the users logged
in to the system:who | wc -l
• If you want to display the output of any command one screen at a time: command | more
example:ls -alF | more
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Protecting files and directories• The ls -l command display detailed listing of a
file, including its protection mode:
drwxrwxrwx owner size directoryname …..-rwxrwxrwx owner size filename …
• the first character (d or -) indicates whether it is a file or directory name.
• The following 9 character indicate the protection mode.
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Protecting files and directoriesrwx rwx rwx
• Each group of three characters describes the access permission: read , write and execute
• the first three settings pertain to the access
permission of the owner of the file or directory, the middle three pertain to the group to which the owner belongs, and the last three pertain to everyone else.
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Access rights on files.• r (or -), indicates read permission, that is, the
presence or absence of permission to read and copy the file
w (or -), indicates write permission; that is, the permission to change a file
x (or -), indicates execution permission; that is, the permission to execute a file, where appropriate
example: -rwxrw-r--
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Access rights on directories. r: allows users to list files in the directory; w: means that users may delete files from the
directory or move files into it. Never give write permission to others to your
home directory or any of its subdirectories. x: means the right to access files in the directory.
This implies that you may read files in the directory if you have read permission on the individual files.
example: drwxrw-r--
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Changing file access permission
chmod (changing protection mode)• Consider each group of three to be a 3-bit number
example: you want to set permission to
rwx r-- --- 111 100 000
7 4 0
chmod 740 filename
chmod codes
Users– u – owner– g – group– o – others– a - all
Access code• r – read• w – write• x- execute
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Examples:chmod g+w filenamechmod o-r filenamechmod a-x filename
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Process & job control• A process is an executing program with a unique
ID (PID).• To display information about your processes with
their PID and status:ps
• to display a list of all processes on the system with full listing
ps -Af
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Process & job control commands• A process may be in the foreground, in the
background, or be suspended. In general the shell does not return the UNIX prompt until the current process has finished executing.
• To run a program in the background, append a & at the end of the command
prog1 &[1] 6259
• system returns the job number and PID
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Process & job control commands• To suspend a running process
CTRL Z• example: % prog
CTRL Z• To background a running processCTRL Zbg
• To bring a process to forgroundfg %job
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Process & job control commands• to kill a background process
kill PID• to suspend a running background process
stop PID
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Process & job control commands• Background process can not use the standard
I/O. ==> Need to redirect I/O
e.g: grep mysort *.c &
output will be lost
grep mysort *.c > file1 &
Kill Command• kill –s STOP PID --- suspend• kill –s CONT PID --- resume• kill –s TERM PID --- terminate
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Compiling C programs
cc [options] file …• by the default, the resulting executable is a.out
cc prog.c
cc -o prog prog.c• names the resulting executable prog instead of a.out
• Compile a C++ programg++ prog.cpp
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Editing files
Available editors:• vi • emacs• picoCheck references on web
vi commandsa – appendi – insertx – eraseEsc – return to command modeShift : - enter file command modew – writeq – quitw! – force writeq! – force quit
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File transfer• WS_FTP - a GUI ftp program• ftp on command prompt
– ftp gator.uhd.edu– After login:
• put – transfer a single file from the current folder on local machine to the current directory on Gator
• mput – upload multiple files• get – transfer a single file from the current directory on Gator
to the local machine• mget – download multiple files• cd – change the current directory on Gator• lcd – change the current folder on the local machine• bye – quit ftp
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Example: Writing a C program on Unix
• Write a program that counts the number of non white-space characters in a text file. Program takes as command argument the name of the input file and displays the output on the standard output.
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// Character Count: Basic Algorithm#include <stdio.h>#define BLANK ' '#define NEWLINE '\n'int main(int argc, char *argv[]){ FILE *infile;
char c;int char_count=0;// count the number of charecters in infilewhile ( (c = getc(infile)) != EOF)
if ((c != BLANK) && (c != NEWLINE) )++char_count;
printf("%d characters\n", char_count);return 0;
}
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Testing the # of command arguments
if (argc != 2){
fprintf(stderr, " %s: expects 1 argument but was given %d\n", argv[0], argc-1);fprintf(stderr, "Usage: %s inputfile \n", argv[0]);exit(1);
}
int printf( char *format, arg1, arg2, ….)
int fprintf( FILE * stream, char *format, arg1, arg2, ….)
Format specifiers used by printf• %c – character• %[n]s – string. n is the width of the field• %[n]d – integer• %[n.m] – floating point number
– n – the width of the field– m – the number of digits in the fractional part
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Opening input fileif ( (infile = fopen(argv[1], "r")) == NULL){
fprintf(stderr,"%s: cannot open %s \n", argv[0], argv[1]);exit(1);
}
File *fopen(char *filename, char *mode);
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file modes"r" : open text file for reading
" w" : for writing
"a" : for appending
"r+" : reading and writing
"w+": for reading and writing (discard existing file)
"a+": open text file for appending
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Count and return # of chars
// count the number of charecters in infilewhile ( (c = getc(infile)) != EOF)
if ((c != BLANK) && (c != NEWLINE) )++char_count;
printf(" %d characters\n ", char_count);return 0;
}
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The End of Quick Unix Tutorial