Scripting Languages and C-Shell

1. Scripting Languages and C-Shell

2. What is a scripting language ? • Script is a sequence of commands written as plain text and run by an interpreter (shell). • Today – some scripting languages have evolved into lightweight programming languages. • Used for lightweight operations such as manipulation of files and prototyping. • Examples: • Shell scripts • Perl • Javascript

3. C-Shell • Unix systems come with a variety of shells, e.g. Bourne (sh), Bash (bash), C (csh), TC (tcsh). • Find your shell: echo $SHELL • C shell startup files: .login, .cshrc • Has C-like syntax

4. Some Shell Metacharacters • # - commnet • “ – quote multiple characters but allow substitution • $ - dereference a shell variable • & - execute in background • ‘ – quote multiple characters • * - match zero or more characters • ? – match a single character • [] – insert wild cards: [0-3,5] • ; - separate commands • ! – refer to event in the history list: !!,!4 • ` - substitute a command • % - refer to a job: %3

5. Some useful c-shell commands • head / tail – returns first / last lines of a file • echo – print command • sort – used to sort strings in lexicographical order • cat – concatenate files and print • grep – find regular expressions in files • find – find files by criteria • wc – word count on files • diff - find differences between files • basename / dirname – extract file / directory name from full path • touch – change file timestamp • mail – sending mail • cp/mv – copy/move files

6. Redirection and pipes prog redirection file • > : redirect stdout • >> : append stdout • >& : redirect stdout and stderr • >>& : append stdout and stderr • < : redirect stdin prog1 pipe prog2 • | : redirect stdout of prog1 to stdin of prog2 • |& : same, with stdout and stderr

7. Some environment variables • home – name of home directory • path – search path • prompt – shell prompt • cwd – current working directory • term – type of terminal • history – length of history recorded

8. How to write a c-shell script • Edit the code file (no mandatory extension) • Make sure the first line in the file is: #!/bin/csh –f • Add executable permission: chmod +x filename

9. #!/bin/csh –f ################ #hello worlds # ################ echo Hello world

10. C-Shell Syntax

11. Defining/changing shell variables • Variables local to current shell: • String: set var1[=strval1]…varN[=strvalN] • Numeric: @ var1[=numval1]…varN[=numvalN] • Global variables: • setenv var [strval] – set and export • $var or ${var} – access value of var Examples: • set name = Alon #string var. • set name = $< #input from user • @ a = 0 #numeric var. • set dir = `pwd` #command substitution

12. Array variables • Available for integers and strings • Indexed starting from 1!!! • Declaration: set name = (array elements) • $#name – number of elements in array • $name[i] – access the ith element • $name[i-j] – elements i to j. Examples: • set students = (David Ron Idit) • set fib = (0 1 1 2 3) • set fib = ($fib 5) #append • set size = $#fib #size==6

13. Passing arguments to scripts • $argv[1]…$argv[9] are assigned the command line arguments • $#argv or $# - total number of arguments • $argv[*] or $* - values of all arguments • $argv[0] or $0 – name of script • shift [variable_name] – in case there are more than 9 arguments – shifts words one position to the left in variable (argv is the default).

14. #!/bin/csh –f ################ #simple_example # ################ # string variable set course = soft1 echo $course # array set names = ( Danny Dina Eyal Ayelet Ori Neta ) echo $names echo $#names # size of array echo $names[2] # the second element echo $names[2-] # starting from the second element echo $names[-2] # until the second element echo $names[2-3] # elements 2,3

15. # numeric variables and expression evaluation @ num = 17 echo $num @ num -= 3 echo $num @ num *= 14 echo $num # if we want to assign the value of a command to a variable set chars = `wc -l ./simple_example` echo $chars # accessing program parameters echo The program name is : $0, the first parameter is $1 and the second is $2 echo The number of parameters \(not including program name\) is $#argv

16. Loops • foreach identifier (set) . . . end • while (expression) . . . end • Expression can include the usual C operators. • break, continue – as in C.

17. Conditional statements • switch (value) • case value1: • breaksw • . . . • default: • endsw • if (expression) command • if (expression) then then-command-list [else if (expression) then then-command-list . . . else else-command-list] endif

18. Testing files attributes • if (-op file_name) then… -r : read access -w : write access -x : execute access -e : existence -o : ownership -f : plain (non-dir.) file -d : directory -l : link

19. #!/bin/csh –f ######## # sum # ######## if ($#argv == 0) then echo Usage: $0 num1 [num2 num3 ...] exit 1 endif @ sum = 0 foreach number ($argv) @ sum += $number end echo The sum is : $sum @ average = $sum / $#argv @ remainder = $sum % $#argv echo The avergae is: $average\($remainder\)

20. #!/bin/csh -f ############ # sort_files # ############ if ($#argv == 0) then echo USAGE: $0 file_names_to_sort echo This command writes on the original files \!\!\! exit 1 endif foreach file($argv) sort $file > $file.tmp mv $file.tmp $file end

21. #!/bin/csh -f # Biggest_file # INPUT: Directory name # OUTPUT: The file with the biggest number of characters in the given directory if ($#argv == 0) then echo USAGE: $0 directory_name exit 1 endif if (-d $1) then @ max = 0 foreach file($1/*) if (-r $file && -f $file) then set wc_out = `wc -c $file` if ($wc_out[1] > $max) then set biggest_file = $wc_out[2] @ max = $wc_out[1] endif else if (!(-r $file)) then echo $file unreadable endif end echo The biggest file is $biggest_file echo The number of characters is $max else echo $1 is not a directory endif

22. #!/bin/csh -f # Modulo3 # INPUT: sequence of integer numbers separated by \n terminated by 0 # OUTPUT: prints the value of each number modulo 3 set num = $< while ($num != 0) @ modulo = $num % 3 switch ($modulo) case 0: echo 0 breaksw case 1: echo 1 breaksw case 2: echo 2 breaksw default: endsw set num = $< end

23. Retrieving returned values • Returned values (by return, exit) are stored in status environment variable • The script: #!/bin/csh -f ./prog if ($status != 0) then echo "Error occured!" endif runs prog (from current dir) and reports whether an error occurred.

24. awk/gawk • Useful utility for file manipulation • Processes input line by line. • Example: gawk ‘{print $1}’ input • For details see : http://www.gnu.org/software/gawk/manual/

25. #!/usr/bin/gawk -f BEGIN { stud_num = total = high_stud_num = total_high = 0} { if (NF != 3) { print "error in line", FNR, ":", $0 next } ++stud_num total += $3 if ($3 > 80) { total_high += $3 ++high_stud_num } } END { print "Number of students: ", stud_num print "Avergae grade is: ", total / stud_num print "Average of high grades is: ", total_high / high_stud_num}

26. Running with input : Ron 033453671 91 Yael 034567832 73 Ran 040478124 100 Yoav 060381253 95 Tal 045623141 78 90 Output is : error in line 5 : Tal 045623141 78 90 Number of students: 4 Avergae grade is: 89.75 Average of high grades is: 95.3333