Unix Shell Scripts

1. Unix Shell Scripts

2. What are scripts ? • Text files in certain format that are run by another program • Examples: • Perl • Javascript • Shell scripts (we learn c-shell scripts)

3. How they differ from C programs ? • C programs are compiled into machine code (executables) • Executables are not portable, but they run faster (no translation during runtime)

4. What to use ? • Use scripts for lightweight operations: • Simple manipulations on files • Sending mails • Network communication • Rapid development • Use c programs for: • CPU bound computations • Complex data structures • Critical time applications • Embedded applications

5. Some useful c-shell commands • head / tail – returns first / last lines of a file • echo – print command • sort – used to sort files in lexicographic 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 • whereis – locate program

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. 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 (for c-shell scripts) #!/bin/awk –f (for awk scripts) • Add executable permission: chmod +x filename

8. #!/bin/csh –f ################ #simple_example # ################ # We can define variables and print their values set course = soft1 echo $course # We can do the same for arrays 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

9. # '@' at the beginning of the line - treat as an arithmetic expression and not # as a string @ 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

10. Loops • foreach identifier (set) . . . end • while (condition) . . . end

11. Conditional statements • if condition then . . . endif • switch (value) case value1: breaksw . . . default: endsw

12. Testing files attributes • if -op file_name -r : read access -w : write access -x : execute access -e : existence -o : ownership -f : plain file -d : directory -l : link

13. #!/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\($remainder\)

14. #!/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

15. #!/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

16. #!/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

17. 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.

18. awk • Useful utility for file manipulation • For details see : http://www.gnu.org/manual/gawk-3.1.1/gawk.html

19. #!/bin/awk -f BEGIN { stud_num = total = high_stud_num = total_high = 0} 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}

20. 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