C Shell Script Introduction

1
Lecture 4

• C Shell Script - Introduction
• Array Variables

2
Shell script/program

• Shell script a series of shell commands placed
  in an ASCII text file
• Commands include
• Anything you can type on the command line
• Variables (including shell vars, env vars,
  command args) and Expressions
• Control statements (if, while, for)

3
Script execution

• Two ways to run a shell script
• Launch a subshell with the script name as the
  argument. e.g. csh my_script.sh
• Specify which shell to use within the script
• First line of script is as !/bin/csh
• Make the script executable using chmod
• Make sure the PATH includes the current directory
• Run directly from the command line
• No compilation is necessary!

4
Shell Script Example

• cat ltlt . gt ./hello.sh
• ? !/bin/csh -f
• ? echo Hello World
• ? .
• chmod x ./hello.sh
• ./hello.sh

5
Variables

• Shell/Environment Variables
• Command Line Arguments
• Array Variables

6
Review Predefined Shell Variables

• argv list of argument passed to the current
  command
• cwd full pathname of current dir
• history number of commands saved in history
• savehist number of history entries to save in
  /.history
• home home dir ()
• path lost of pathnames to search for commands
  to execute
• shell name of shell in use (ex /bin/csh)
• status exit status of last command

7
Review Shell Variables Expressions

• Use some variables expression, we can also
  extract other info. about the shell variables
• var or var value of variable var
• ?var 1- if var is set 0 if var is not set
• var1 first word in the value of var
• var-10 words 1-10 in var
• var2- words staring from word 2
• var all words in the value of var
• 0 name of the program being executed
• lt read a line from stdin
• var number of words in var

8
Review Command Arguments

• 0 command name
• n argument number n
• - first argument
• - last argument
• n-m arguments n through m
• n - arguments n through the last one
• - All arguments

9
Array variables

• Array is a list of values
• To assign values to array variables, use ()
• Reference a value by nameindex
• a3
• a (same as a0)
• sports(ball frisbee puck)
• Index is 1 based
• Some of the predefined shell vars are array vars,
  such as argv (args), path (dirs)

10
Array Variable Examples

• echo path
• /bin /usr/bin /usr/local/bin /cs459_11/bin
• echo path
• 4
• echo path0
• echo path1
• /bin
• set numbers (one two three)

11
Expressions

• C Shell expressions are used with _at_ or with
  (if/while) statements, where variable can be
• Expression are formed by variables operators
• _at_ operator assigns the value of arithmetic
  expressions to a variable
• Example of _at_
• set n2
• _at_ an 2
• _at_ a2
• _at_ b (a gtgt 1) 1

12
Operators

• Arithmetic operators
• Assignment Operators ( , , -)
• Comparison Operators (, !, lt)
• Bitwise and logic operators (!, , ), (gtgt, ltlt)

13
File test operators (operator filename)

• -d file the file is a dir?
• -e file the file exists?
• -f file the file is a plain file?
• -o file the user owns the file
• -r/w/x file the user has read/write/execute
  permission
• -z file the file has 0 size
• ! any above reverse the meaning

14
Control Statements

• if thenelseendif
• if condition
• then
• statements
• else
• statements
• endif
• Whileend
• Syntax
• while condition
• statements
• end
• foreach...end
• foreach var in list
• statements
• done