Cis 216 – shell scripting
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The document provides an overview of common Linux commands and their functions, such as RMDIR to remove empty directories, CHMOD to change file permissions, GREP for pattern matching, FIND to locate files, ECHO to output text, and MORE to view files page by page. It also covers operators like pipes, logical operators, redirection, and command substitution. The document concludes with descriptions of conditional statements like IF/THEN, FOR, WHILE, UNTIL, and CASE that allow scripts to perform actions conditionally.
![ $(( )) – evaluates the enclosed expression
[ ] – test an expression to see if it is true or false
< > - used to compare values or strings
$( ) – command substitution – great when doing
logical OR’s or AND’s](https://image.slidesharecdn.com/cis216shellscripting-130401103032-phpapp01/85/Cis-216-shell-scripting-7-320.jpg)
![ How to get your script to do more useful stuff
If. Then
if [test]
Then
stuff I want the computer to do
fi
If. Then. Else
if [test]
Then
stuff I want the computer to do
Else
Stuff I want the computer to do if the first condition didn’t happen
fi](https://image.slidesharecdn.com/cis216shellscripting-130401103032-phpapp01/85/Cis-216-shell-scripting-10-320.jpg)
Cis 216 – shell scripting
- 1. Remembering the basics – Week 1 Dan Morrill April 01 2013
- 2. RMDIR – removes a directory only if it is empty RMDIR –r – removes a directory regardless if it is empty or not CHMOD 777 –r /user/dan – recursively changes the permissions of the directory /user/dan to RWXRWXRWX grep – pattern matching for example ps –ef |grep apache2 will look for all processes running under the name apache2 egrep – used in regular expressions
- 3. find – find the location of a file (or files) on a hard drive at the command line echo – writes data to the screen (standard output) The TTY – Screen is always standard output (STDOUT) more – displays the contents of a file one page at a time (hard for long files like syslog) clear – clears the screen of text and provides the command prompt chown – change the owner of a file or directory rm – remove a file
- 4. mv – move a file to a new place and or new name chgrp – change the group ownership of a file mkdir – make a directory ls – list the files in a directory, ls –la show the long form (including permissions and owners) of the files in a directory cat – an alternative to showing the data in a file all at once pwd – display the current directory passwd – change the password of the currently logged in user
- 5. >> - append data to the END of a file > - overwrites the file and any data in it | - pipe character – strings commands together || - logical OR – in that A || B in a loop, condition A or condition B & - executes your process in the background – so you can still use the command line ./script.sh & will run your process in the background && - Logical AND A && B if A succeeds, run B sleep – stop execution of the script for a specified number of seconds sleep 20 means sleep for 20 seconds
- 6. diff – compares two files (this is great for seeing what changes were made in a script against the original and modified) sdiff – only works with the 132 character display, but compares files side by side lp – prints a file to the configured printer lpstat – shows the user what is in the printer queue ( ) – runs the enclosed command in a sub-shell (( )) – evaluates and assigns a value to a variable and does math in a sub-shell
- 7. $(( )) – evaluates the enclosed expression [ ] – test an expression to see if it is true or false < > - used to compare values or strings $( ) – command substitution – great when doing logical OR’s or AND’s
- 8. ++ - auto increment a value for I=1 ++ (takes I up by 1 for every loop) -- - auto decrement a value for I=100 -- (takes I down by 1 for every loop) <= - less than or equal to >= - greater than or equal to
- 9. I will expect to see this in the header of every Unix Script you will turn in: #!/bin/sh (tells the computer to use a bourne shell) # # Script: Name of script (what you named this file) # Author: Your Name (so I know who wrote it) #Date: (the date you wrote it) #Revision: 1.1.A(how many times it changed, and what state it is in(A, B, D, T or P) All scripts should also have A, B, D, T or P at the end of the revision statement so I know if it is Alpha, Beta, Dev, Test, or Production. All scripts turned in should be production scripts
- 10. How to get your script to do more useful stuff If. Then if [test] Then stuff I want the computer to do fi If. Then. Else if [test] Then stuff I want the computer to do Else Stuff I want the computer to do if the first condition didn’t happen fi
- 11. for for A=1 do stuff I want the computer to do done While While A=1 do stuff I want the computer to do done
- 12. Until until A=1 do stuff I want the computer to do done Case case A=1 stuff I want the computer to do case A != 1 stuff I want the computer to do easc