Cis 216 – shell scripting

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A small primer for my CIS 216 class on shell scripting

A small primer for my CIS 216 class on shell scripting

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  • 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