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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Getting access to a Unix system

• From Web Browser
• telnet//gator.uhd.edu

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Logging in the first time

• Change your password
• passwd
• 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 topic
• man -k keyword
• For more information on using the man pages
• man man

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Getting Help from the System

• Once you know the man pages you need
• man section name
• e.g. man write
• The name may be used for a command, a system
  call, a library function, etc.
• Each is described in a different section of the
  man pages
• e.g write(1) is a command to send a msg
• write(2) is a library function that writes to
  a file

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Getting Help from the System

• man 2 write
• displays the man pages of write(2)
• For more information on using the man pages
• man 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 users 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 youre using
• echo SHELL
• --gt /bin/tcsh
• To change to another shell
• chsh

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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.
• gt 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 directory
• ls -lF pathname
• where 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 proj125
• cat proj1-7

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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
  users home directory.
• e.g ls smith
• lists 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 directory

• cd (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)
• gt pwd
• /home/student/smith

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Copying files

• cp (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 pathname2
• e.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 path
• rmdir -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 monitor
• cat 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 lines
• tail -- displays last 10 lines

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Searching the contents of a file

• Searching using more
• For 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
• gt grep music myfile
• To ignore upper/lower case distinctions, use the
  -i option
• gt 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 both
• wc myfile

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Other Useful Commands

• who
• lists on the screen all the users currently
  logged to the system
• finger username
• lists 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).
• lt redirect input
• gt and gtgt redirect output
• Example
• who gt namelist
• who gtgt namelist
• sort lt namelist
• sort lt namelist gt newnamelist
• sort lt namelist gt 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 gt file1

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Using redirection to concatenate files

• Examples
• cat file1 gt file2
• copies file1 into file2
• To concatenate files
• cat file1 file2 gt file3
• or
• cat file2 gtgt 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 gt namelist
• sort 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 directories

• rwx 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

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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 process
• CTRL Z
• bg
• To bring a process to forground
• fg PID

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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.
  gt Need to redirect I/O
• e.g grep mysort .c
• output will be lost
• grep mysort .c gt file1

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Process job control commands

• A job is a group of one or more processes
• To list all the jobs that are in the background
• jobs
• 1 Running
• 2 - Running
• To bring a background job to the foreground
• fg job-no
• e.g fg 2

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Process job control commands

• to kill a background job
• kill job-no
• to suspend a running background job
• stop job-no

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Process job control commands

• To run a process in the background, even after
  logging out
• nohup prog1

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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

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Editing files

• Available editors
• vi
• emacs
• pico
• Check references on web

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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 ltstdio.hgt
• define BLANK ' '
• define NEWLINE '\n'
• int main(int argc, char argv)
• FILE infile
• char c
• int char_count0
• // count the number of charecters in infile
• while ( (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", argv0, argc-1)
• fprintf(stderr, "Usage s inputfile \n",
  argv0)
• exit(1)

int printf( char format, arg1, arg2, .) int
fprintf( FILE stream, char format, arg1, arg2,
.)
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Opening input file

• if ( (infile fopen(argv1, "r")) NULL)
• fprintf(stderr,"s cannot open s \n", argv0,
  argv1)
• 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 infile
• while ( (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