Conquering the Bash Shell

1. Conquering the Bash Shell

2. Overview • Shell Evironment • Linux Command Prompt • Viewing System Information • Advance Shell Usage and Script

3. Shell Environment • 2 user interfaces on Linux • GUI hosted by X • CLI called the shell • The most common way to access the shell is via a terminal window • Start > System Tools > Terminal • Example : $ w • The w command tells Linux to display the system status and a list of all system users

4. Shell Environment (cont…) • Example : $ date • The date command tell linux to show the current date • How to correct commands • Backspacekey erases characters • Left keydoes not erase characters • Delete key to delete unwanted characters

5. Shell Environment (cont…) • Reissue previous command using bash's history • Scroll back (the Up arrow key)or • Back down (the Down arrow key) • Bash's history is saved in the user's home directory, ~/.bash_history • Up to 500 command • Make command completion • Type a part of your command • Press Tab key

6. Shell Environment (cont…) • Useful Control keystrokes • Ctrl-C — cancels execution • Ctrl-D — terminate console input • Ctrl-Z — suspends the currently executing program • Special characters • # — Marks the line as a comment • ; — Separates commands

7. Linux Command Prompts • Command Prompt Forms • Getting Help • Working with Directories • Working with Files • Working with Compressed Files

8. Command Prompt Forms • Commands and Arguments in Linux • command [options] [arguments] • 2 kinds of commands • External commands • Stored in /bin, /usr/bin, or /usr/local/bin • System administration commands • stored in /sbin or /usr/sbin - included by default in the path of the root user • Linux commands are case sensitive

9. Command Prompt Forms (cont…) • Options modify the way that a command works • Example • w -h • w informit • w -h informit • When your command is too long • Type a backslash (\) at the end of a line, then • Press Enter, then • Continue your command in the new line

10. Getting Help • 2 way of getting help in Linux • man command • apropos command • Both of them access a help database that describes commands and their options • Each Linux command is described by a special file called a manual page • $ man w • To quit from mode man, type “q”

11. Getting Help(cont…) • The apropos command displays just a one-line summary of each $ apropos samba • Before using apropos, run this $ makewhatis

12. Working with Directories • Displaying the working directory $ pwd • Changing the working directory $ cd /bin (go to bin directory) $ cd (go to your home directory) $ cd .. (go to the parent directory)

13. Working with Directories (cont…) • Display directory contents $ ls $ ls –l $ ls /bin $ ls –al • Use less to show output one page at a time $ ls | less • space moves one page forward • b moves one page backward

14. Working with Directories (cont…) • Creating a directory $ mkdir office # mkdir /tmp/documents • Removing a directory $ rmdir unwanted

15. Working with Files • Displaying the contents of a file # cat /etc/passwd # less /etc/passwd • Removing a file # rm badfile • Copying a file # cp /etc/passwd sample • Renaming or moving a file # mv old new • Finding a file # find . -name 'missing' -print # find / -name '*iss*' -print # locate pass # which ls

16. Working with Files(cont…) • To link a new name to an existing file or directory # ln -s old new • To run the program # bigdeal or # ./bigdeal or # /home/bob/bigdeal

17. Working with Compressed Files • To compress files # gzip bigfile.gz • To expand a compressed file # gunzip bigfile • To create a tarfile # tar -cvf backup.tar /home/informit • To list the contents of a tarfile #tar -tvf tarfile | less • To extract the contents of a tarfile #tar -xvf tarfile

18. Further with File Permissions • To set the access modes of a directory or file # chmod nnn directory-or-file • To assignnewuser as the owner of the file hotpotato # chown newuser hotpotato • To assigns newgroup as the new group of the file hotpotato # chgrp newgroup hotpotato • To change user login group to the group named secondgroup # newgrp secondgroup

19. Viewing System Information • CLI also provide command to troubleshoot system problems and identify resource bottlenecks • Each supports options and arguments to customize its operation and output • Example : • du, df, free, top, ps, uptime

20. Advance Shell Usage and Script • Filename Globbing • Shell Aliases • Jobs • Shell Scripts • Redirection and Piping • Filter & Regular Expressions • Shell Variables • The Search Path • Quoted Strings

21. Filename Globbing • Globbing can make the command writing more quick and effecient • Example : • Common command : $ ls -l file1 file2 file3 file04 • Using File Globbing : $ ls -l file* • Another form of file globbing • List file2 and file3 $ ls -l file[2-3]

22. Shell Aliases • Make commands easier to use • Establish abbreviated command names • Pre-specify common options and arguments for a command • Form : alias name='command' • Example : $ alias lihat='ls -l' $ unalias lihat

23. Jobs • Jobs are command execution process • 2 mode of jobs : • Foreground • Background • 4 activities related with jobs : • Run jobs in the background • Notify when a job ends • Bring jobs to the foreground • Stop and Suspend jobs

24. Jobs (cont…) • Example : • Run jobs in the background $ lpr mydata & • Notify when job ends $ notify %2 • Bring jobs to the foreground $ fg %2 • Stop and Suspend jobs $ kill %2

25. Shell Scripts • Definition : • A file that contains a set of commands to be run by the shell when invoked • Example : • file name : deleter echo -n Deleting the temporary files rm -f *.tmpecho Done. • Running it$ sh deleter

26. Shell Scripts (cont…) • 2 kinds of scripts : • Standard Scripts ~provided by Linux • User Scripts ~ created by user

27. Redirection • 3 standard data streams • stdin (<) • Where program read their input • stdout (>) • Where program write their output • stderr (2>) • Where program write the error message

28. Redirection(cont…) • Example : • Redirect number of lines, words and character on /etc/passwd into total $ wc /etc/passwd > total • Redirect an error message to /dev/null $ grep localhost * 2> /dev/null • Tell wc to read from a file, rather than the console $ wc < /etc/passwd

29. Filter • Filters are commands that • Read data • Perform operations on that data • Send the results to the standard output • Example : $ cat complist | lpr $ ls –al | grep root

30. grep Command • Form : • greppattern filenames-list • Example : $ grep 'text file' preface $ grep data preface intro $ grep data * $ grep while *.c

31. Regular Expressions • Usually, combined with grep, sed, gawk command • Notation : ^, $, *, ., [] • Example : $ ls -l | grep '^d‘ $ grep ‘t$‘ file1 $ ls –l | grep ‘file[1-3]’

32. Shell Variables • Provides a convenient way of transferring values from one command to another

33. Shell Variables (cont…) • To list shell variables : $ set | less • To export a variable : $ export variable-name • Example : $ cd ${HOME} $ cd ${HOME}/work $ echo ${HOME}

34. The Search Path • The paths that are looked in by shell when issuing an external command • Use a colon (:) to separate each path of the search path • /usr/bin:/bin:/usr/local/bin • To make additional path : $ PATH=${PATH}:/home/bill $ PATH=/home/bill:${PATH} • To find location of program file : $ which program-name

35. Quoted Strings • Ensures that the shell doesn’t misinterpret a command • argument, file name, variable • Example $ echo $PATH $ echo ’$PATH’ $ echo My home directory contains ‘ls ~|wc -?‘ files.

36. Summary • In this module, you have learned about : • Shell Command • Linux Command Prompt • Viewing System Information • Advance Shell Usage and Script