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Shell Commands

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Developed by Steve Bourne at AT&T. Korn shell. Developed by David Korn at AT&T. C-shell ... The shell interprets the commands you typed and tries to find the ... – PowerPoint PPT presentation

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Title: Shell Commands


1
Shell Commands
  • Chapter 1.4

2
Shells
  • What is a shell?
  • Bourne shell
  • Developed by Steve Bourne at ATT
  • Korn shell
  • Developed by David Korn at ATT
  • C-shell
  • Developed by Bill Joy for Berkeley Unix
  • EZ-shell
  • Developed by somebody at UWM.

3
How the shell works
  • Shell displays a prompt.
  • You type in a command.
  • You press the return key.
  • The shell interprets the commands you typed and
    tries to find the correct programs to run.
  • The kernel runs the requested programs and
    returns the results to the shell.
  • The shell displays the command prompt again.

4
Standard Input, Output and Error
  • Standard input
  • stdin
  • The place the program normally looks for input.
  • The keyboard.
  • Standard output
  • stdout
  • The place where the program normally sends its
    output.
  • The screen.
  • Standard error
  • stderr
  • Used by programs to display error messages.
  • Also the screen.

5
Redirection ,
  • Redirects the standard input
  • command
  • The command will open the file and use its
    content as its source of input

6
Redirection ,
  • Redirects the standard output.
  • command file name
  • The results of the command will be sent to the
    specified file.
  • Will create or overwrite the destination file.
  • cat june july aug summer2000

7
Redirection ,
  • Also redirects the standard output.
  • command file name
  • The results of the command will be sent to the
    specified file.
  • Will append the results of the command to the
    existing file.

8
Grouping commands
  • Executing one command at at time can be tedious.
  • Unix allows for grouping of commands by
    separating commands with a semi-colon ().
  • pwd cal 1 2000 date

9
(pipe)
  • Similar to redirection and grouping.
  • Used to link commands.
  • command command etc.
  • The output of the first command is sent as the
    input to the second command, and so on, and so on
  • who more

10
Wildcards
  • Typing in Unix can be tedious.
  • Unix supports three wild-card characters
  • Asterisk () matches any string of characters
    including blanks.
  • Question mark (?) matches single characters.
  • Square brackest () Tells the shell to match
    any characters that appear inside the brackets.
  • Quoting special characters

11
wc
  • word count
  • Used to display a word count of a file
  • wc -c l w file name(s)
  • The output you will see will be a line showing
    the number of lines, words and characters
  • Limit display with the flags

12
sort
  • Sorts the contents of a file
  • sort -b f n r u file name(s)
  • Takes the contents of a file and displays it in
    sorted order
  • Flags
  • -b ignores blanks
  • -f folds upper- and lowercase letters together
  • -n numeric sort
  • -r reverse usual order
  • -u prints duplicate entries only once

13
Job control
  • Unix works via jobs or processes
  • Every command or program is a separate
    job/process executed by a user
  • Jobs are usually run in the foreground, but can
    be made to run in the background
  • Jobs can be killed by the user who created them

14
Job control
  • ctrl-c cancels a command/job
  • ctrl-z suspends a command/job
  • jobs
  • Lists the jobs (programs) that you currently have
    running.

15
bg
  • Forces a job to the background
  • First, type a ctrl-z to suspend the job
  • Then type bg and the job is forced to the
    background
  • Use the jobs command to see it
  • You can force a job to the background immediately
    with the

16
fg
  • Brings a job to the foreground.
  • Use the jobs command to see the jobs you have
    running.
  • Type fg number and that job will be brought to
    the foreground.

17
kill
  • Kills a job that you have running.
  • Use the jobs command to see what you have
    running.
  • Type kill number.
  • Not the most graceful way out, but it works.
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