A small primer for my CIS 216 class on 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