Week 5 notes

Variables - Enviornment variables are named pieces of data, initilized by a shell or by a script run in that shell.

Logical statments - There are a few core constructs in programming. Versions of these are avilible in most shells.

Return Values - When a progam finishes it may set a variable on the way out. This is called a return value.

Continuing Borne shell

Variables

• $@ - quoted array containing arguments passed at the command line
• $# - Number of arguments passed at command line
• $? - last exit or return value
• $! - Process ID of last command exaecuted
• $- - Last assigned end variable.
• $$ - Process ID of current shell
• $8 - Eighth argument passed to last command
• $string - any variable name you want

• %+ - most recent process
• %- - second most recent
• %8 - 8th most recent process

• [control] [z] - send job to background and stop
• bg - tell background job to start
• fg - bring backgound job to foreground
• jobs - list background jobs in this shell

• program1 && program2 - If preceeding program returns success run following program
• program1 || program2 - If preceeding program returns failure run following program
• if condition,then,elifcondition,then,else,fi - string of if conditionals
• whilecondition,do,done - srting of while commands
• casevariable,in,possibile varible 1,),command(s),;;,possibile variable 2,),command(s),;;,esac - string of case conditionals

Aditional Borne stuff

• \char - print the following character literally.
• return - return following integer or variable
• read - read in a variable until newline is reached

Script Homework

namekill - write a script that takes a string of characters as an argument and kills all processes containng that string in their name.

userprog - Using the w command in a script, list all users running a program containing a string of characters passed as an agrument to the script.

extra credit... userprogbg - Just like userprog but it does error checking (a simple test should do it: hint hint) to see if an argument was passed.