Cis 216 – shell scripting

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 willexpect 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 toget 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