1. Advanced C Shell Programming
Chapter 18
Advanced C Shell
Programming

2. Objectives To discuss numeric data processing
To describe array processing
To discuss how standard input of a command in a shell script can be redirected to data within the script
To explain signal/interrupt processing capability of the C shell
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3. Numeric Data Processing
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4. Numeric Data Processing
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5. Numeric Data Processing
value1 = 10
value2 = 15
% echo “$value1 $value2”
10 15 %
difference = ($value1 - $value2) sum = ($value1 + $value2)
% echo $difference $sum
-5 25
results++
results += 1
results = ( $results + 1 )
% set side = 10 area volume
area = $side * $side
volume = $side * $side * $side
% echo $side $area $volume
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6. Array Processing
An array is a named collection of items of the same type stored in contigous memory locations
Array items are numbered with the first item being 1
% set students = (David James Jeremy Brian Art Charlie)
% echo $students
David James Jeremy Brian Art Charlie
% echo $#students 6
% echo $?students 1 %
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7. Array Processing % echo $students[2] James
% set students[2] = “Mansoor Sarwar”
% echo $students
David Mansoor Sarwar Jeremy Brian Art Charlie
Mansoor Sarwar %
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8. Array Processing % unset students % echo $students
students: Undefined variable. %
% set files = `ls` numfiles = `ls | wc -w`
% echo $files
cmdargs_demo foreach_demo1 if_demo1 if_demo2 keyin_demo
% echo $numfiles 5
% echo $files[3]
if_demo1
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9. Array Processing % cat num_array_demo #!/bin/csh
# Initialize Fibonacci array to any number of Fibonacci numbers - first ten in this case
set Fibonacci = ( )
@ size = $#Fibonacci # Size of the Fibonacci array
@ index = 1 # Array index initialized to point to the first element
@ sum = 0 # Running sum initialized to 0
while ( $index <= $size )
@ sum = $sum + $Fibonacci[$index] # Update the running sum
@ index++ # Increment array index by 1
end
echo “The sum of the given $#Fibonacci numbers is $sum.”
exit 0
% num_array_demo
The sum of the given 10 numbers is 88. %
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10. The Here Document
The here document feature of the C shell allows you to redirect standard input of a command in a script and attach it to data within the script
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11. The Here Document % cat heredoc_demo #!/bin/csh # First example
cat << DataTag
This is a simple use of the here document. These data are the
input to the cat command.
DataTag
# Second example
mail $argv[1] << WRAPPER
Hello,
This is a reminder for the weekly meeting tomorrow.
Mansoor
WRAPPER
echo “Sending mail to $argv[1] ... done”
exit 0
% heredoc_demo eecsfaculty
Sending mail to eecsfaculty ... done %
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12. The Here Document % more dext #!/bin/csh if ( $#argv == 0 ) then
echo “Usage: $0 name”
exit 1
else
set user_input = “$argv[1]”
grep -i “$user_input” \ \
<< Directory_Data
John Doe
Jenny Great
David Nice
Jim Davis
Art Pohm
Directory_Data
endif
exit 0 %
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13. Interrupt (Signal) Processing
Three possible actions that the process receiving the signal can take:
Accept the default action as determined by the UNIX kernel
Ignore the signal
Take a programmer defined action
Hardware interrupt e.g keyboard interrupt(<Ctrl-C>)
Signal received due to termination of a child process
Accessing a main memory location that is not part of the process’s address space
Software termination
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14. Interrupt (Signal) Processing
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15. Interrupt (Signal) Processing
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16. Interrupt (Signal) Processing
% cat onintr_demo
#!/bin/csh
backagain: # Intercept <Ctrl-C> and transfer control to the command at
onintr interrupt
set secretcode = agent007 # Set secret code
echo “Guess the code\!” # Get user input
echo -n “Enter your guess: “
set yourguess = `head -1`
while ( “$secretcode” != “$yourguess” )
echo “Good guess but wrong. Try again\!”
end
echo “Wow! You are a genius\!”
exit 0
interrupt: # Code executed when you press <Ctrl-C>
echo “Nice try -- you cannot terminate me by <Ctrl-C>\!”
goto backagain %
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17. Interrupt (Signal) Processing
% onintr_demo
Guess the code!
Enter your guess: codecracker
Good guess but wrong. Try again!
Enter your guess: <Ctrl-C>
Nice try -- you cannot terminate me by <Ctrl-C>!
Enter your guess: agent007
Wow! You are a genius! %
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18. Debugging Shell Programs
The C shell programs can be debugged by using the –x and –v options of the csh command
This allows viewing the commands in the user’s script after the variable substitution but before execution
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19. Debugging Shell Programs
% cat debug_demo
#!/bin/csh
echo -n “Enter a digit: “
set var1 = `head -1`
if ( ( “$var1” >= 1 ) && ( “$var1” <= 9 ) ) then
echo “Good input!”
endif
exit 0
% debug_demo
Enter a digit: 4
“: Event not found %
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20. Debugging Shell Programs
$ csh -xv debug_demo
echo -n “Enter a digit: “
echo -n Enter a digit:
Enter a digit: set var1 = `head -1`
set var1 = `head -1`
head -1 4
if ( ( “$var1” > = 1 ) && ( “$var1” < = 9 ) ) then
if ( ( 4 > = 1 ) && ( 4 < = 9 ) ) then
echo “Good input!”
“: Event not found $
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