Appendix B WORKSHOP. SYS-ED/ Computer Education Techniques, Inc.

Transcription

1 Appendix B WORKSHOP SYS-ED/ Computer Education Techniques, Inc.

2 1 Scalar Variables 1. Write a Perl program that reads in a number, multiplies it by 2, and prints the result. 2. Write a Perl program that reads in two numbers and does the following: It prints Error: can't divide by zero if the second number is 0. If the first number is 0 or the second number is 1, it just prints the first number (because no division is necessary). In all other cases, it divides the first number by the second number and prints the result. 3. Write a Perl program that uses the while statement to print out the first 10 numbers (1-10) in ascending order. 4. Write a Perl program that uses the until statement to print out the first 10 numbers in descending order (10-1). COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 1

3 1.1 Solutions - Scalar Variables 1. One solution: print ("Enter a number to be multiplied by 2:\n"); $number = <STDIN>; chop ($number); $number = $number * 2; print ("The result is ", $number, "\n"); 2. Another solution would be: print ("Enter the dividend (number to divide):\n"); $dividend = <STDIN>; chop ($dividend); print ("Enter the divisor (number to divide by):\n"); $divisor = <STDIN>; chop ($divisor); if ($divisor == 0) { print ("Error: can't divide by zero!\n"); elsif ($dividend == 0) { $result = $dividend; elsif ($divisor == 1) { $result = $dividend; else { $result = $divisor / $dividend; if ($divisor == 0) { # skip the print, since we detected an error else { print ("The result is ", $result, "\n"); 3. One solution would be: $count = 1; $done = 0; while ($done == 0) { print ($count, "\n"); if ($count == 10) { $done = 1; $count = $count + 1; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 2

4 A solution is: $count = 10; until ($count == 0) { print ($count, "\n"); $count = $count - 1; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 3

5 2 Perl Operators 1. Write a program that uses the << operator to print out the first 16 powers of Rewrite the following statement using the conditional operator: if ($var1 == 5 $var2 == 7) { $result = $var1 * $var ; else { print("condition is false\n"); $result = 0; 3. Rewrite the following expression using the if and else statements: $result = $var1 <= 26? ++$var2 : 0; 4. Write a program that reads two integers from standard input (one at a time), divides the first one by the second one, and prints out the quotient (the result) and the remainder. 5. Why might the following statement not assign the value 5.1 to $result? $result = ; 6. Determine the order of operations in the following statement, and add parentheses to the statement to indicate this order: $result = $var1 * 2 << $var2 ** 3, $var3; 7. What value is assigned to $result by the following code? $var1 = 43; $var2 = 16; $result = ++$var2 == 17? $var1++ * 2-5 : ++$var1 * 3-11; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 4

6 2.1 Solutions - Perl Operators 1. This is one of several answers: $value = 1; $counter = 0; while ($counter < 16) { print ("2 to the power $counter is $value\n"); $value = $value << 1; $counter++; 2. The answer is: $result = $var1 == 5 $var2 == 7? $var1 * $var : (print("condition is false\n"), 0); 3. The answer is: if ($var1 <= 26) { $result = ++$var2; else { $result = 0; 4. This is one of several answers: print("enter the integer to be divided:\n"); $dividend = <STDIN>; print("enter the integer to divide by:\n"); $divisor = <STDIN>; # check for division by zero if ($divisor == 0) { print("error: can't divide by zero\n"); else { $quotient = $dividend / $divisor; $remainder = $dividend % $divisor; print("the result is $quotient\n"); print("the remainder is $remainder\n"); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 5

7 5. Adding and then subtracting it will cause errors in rounding. This means that the final value will not be identical to ($result = ((($var1 * 2) << (5 + 3)) ($var2 ** 3))), $var3; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 6

8 3 Arrays 1. Write a program that counts all occurrences of the word the in the standard input file. 2. Write a program that reads lines of input containing numbers, each of which is separated by exactly one space, and prints out the following: a. The total for each line b. The grand total 3. Write a program that reads all input from the standard input file and sorts all the words in reverse order, printing out one word per line with duplicates omitted. COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 7

9 3.1 Solutions - Arrays 1. One solution is: $thecount = 0; $line = <STDIN>; while ($line ne "") { chop = split(/ /, $line); $wordindex = 1; while ($wordindex { if ($words[$wordindex-1] eq "the") { $thecount += 1; $wordindex++; $line = <STDIN>; print ("Total occurrences of \"the\": $thecount\n"); 2. Another solution is: $grandtotal = 0; $line = <STDIN>; while ($line ne "") { $linetotal = = split(/ /, $line); $numbercount = 1; while ($numbercount { $linetotal += $numbers[$numbercount-1]; $numbercount++; print("line total: $linetotal\n"); $grandtotal += $linetotal; $line = <STDIN>; print("grand total: $grandtotal\n"); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 8

10 3. One solution = <STDIN>; chop (@lines); $longlongline = = split(/ /, = reverse sort (@words); $index = 0; print("words sorted in reverse order:\n"); while ($index { # note that the first time through, the following # comparison references $words[-1]. This is all # right, as $words[-1] is replaced by the null # string, and we want the first word to be printed if ($words[$index] ne $words[$index-1]) { print ("$words[$index]\n"); $index++; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 9

11 4 I/O 1. Write a program that takes the values on the command line, adds them together, and prints the result. 2. Write a program that takes a list of files from the command line and examines their size. If a file is bigger than 10,000 bytes, print; File name is a big file! where name is a placeholder for the name of the big file. 3. Write a program that copies a file named file1 to file2, and then appends another copy of file1 to file2. 4. Write a program that counts the total number of words in the files specified on the command line. After it has counted the words, a message is sent to user ID dave indicating the total number of words. 5. Write a program that takes a list of files and indicates, for each file, whether the user has read, write, or execute permission. COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 10

12 4.1 Solutions - I/O 1. One solution is: $total = 0; $count = 1; while ($count { $total += $ARGV[$count-1]; $count++; print ("The total is $total.\n"); 2. Another solution is: $count = 1; while ($count { if (-e $ARGV[$count-1] && -s $ARGV[$count-1] > 10000) { print ("File $ARGV[$count-1] is a big file!\n"); $count++; 3. One solution is: open (INFILE, "file1") die ("Can't open file1 for reading\n"); open (OUTFILE, ">file2") die ("Can't open file2 for writing\n"); # the following only works if file1 isn't too = <INFILE>; print OUTFILE (@contents); # we don't really need the call to close, but they # make things a little clearer close (OUTFILE); open (OUTFILE, ">>file2") die ("Can't append to file2\n"); print OUTFILE (@contents); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 11

13 4. One solution is: $wordcount = 0; while ($line = <>) { # this isn't the best possible pattern to split with, # but it'll do until you've finished Day = split(/ /, $line); $wordcount open (MESSAGE, " mail dave") die ("Can't mail to userid dave.\n"); print MESSAGE ("Total number of words: $wordcount\n"); close (MESSAGE); 5. One solution is: $count = 1; while ($count { print ("File $ARGV[$count-1]:"); if (!(-e $ARGV[$count-1])) { print (" does not exist\n"); else { if (-r $ARGV[$count-1]) { print (" read"); if (-w $ARGV[$count-1]) { print (" write"); if (-x $ARGV[$count-1]) { print (" execute"); print ("\n"); $count++; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 12

14 5 Patterns 1. Write a program that reads all the input from the standard input file, converts all the vowels (except y) to uppercase, and prints the result on the standard output file. 2. Write a program that counts the number of times each digit appears in the standard input file. Print the total for each digit and the sum of all the totals. 3. Write a program that reverses the order of the first three words of each input line (from the standard input file) using the substitution operator. Leave the spacing unchanged, and print each resulting line. 4. Write a program that adds 1 to every number in the standard input file. Print the results. COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 13

15 5.1 Solutions - Patterns 1. One solution is: while ($line = <STDIN>) { $line =~ tr/aeiou/aeiou/; print ($line); 2. Another solution is: while ($inputline = <STDIN>) { $inputline =~ tr/0-9/ /c; $inputline =~ s/ = split(//, $inputline); $total $count = 1; while ($count { $dtotal[$digits[$count-1]] += 1; $count++; print ("Total number of digits found: $total\n"); print ("Breakdown:\n"); $count = 0; while ($count <= 9) { if ($dtotal[$count] > 0) { print ("\tdigit $count: $dtotal[$count]\n"); $count++; 3. One solution is: while ($line = <STDIN>) { $line =~ s/(\w+)(\s+)(\w+)(\s+)(\w+)/$5$2$3$4$1/; print ($line); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 14

16 4. One solution is: while ($line = <STDIN>) { $line =~ s/\d+/$&+1/eg; print ($line); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 15

17 6 Control 1. Write a program that uses the do statement to print the numbers from 1 to Write a program that uses the for statement to print the numbers from 1 to Write a program that uses a loop to read and write five lines of input. Use the last statement to exit the loop if there are less than five lines to read. 4. Write a program that loops through the numbers 1 to 20, printing the even-numbered values. Use the next statement to skip over the odd-numbered values. 5. Write a program that uses the foreach statement to check each word in the standard input file. Print the line numbers of all occurrences of the word the (in uppercase, lowercase, or mixed case). 6. Write a program that uses a while loop and a continue statement to print the integers from 10 down to 1. COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 16

18 6.1 Solution - Control 1. One solution is: $count = 1; do { print ("$count\n"); $count++; while ($count <= 10); 2. One solution is: for ($count = 1; $count <= 10; $count++) { print ("$count\n"); 3. One solution is: for ($count = 1; $count <= 5; $count++) { $line = <STDIN>; last if ($line eq ""); print ($line); 4. One solution is: for ($count = 1; $count <= 20; $count++) { next if ($count % 2 == 1); print ("$count\n"); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 17

19 5. One solution is: $linenum = 0; while ($line = <STDIN>) { $linenum += 1; $occurs = 0; $line =~ = split(/\s+/, $line); foreach $word (@words) { $occurs += 1 if ($word eq "the"); if ($occurs > 0) { print ("line $linenum: $occurs occurrences\n"); 6. One solution is: $count = 10; while ($count >= 1) { print ("$count\n"); continue { $count-; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 18

20 6.2 Subroutines 1. Write a subroutine that takes two arguments, adds them together, and returns the result. 2. Write a subroutine that counts the number of occurrences of the letter t in a string which will then be passed to the subroutine. The subroutine must return the number of occurrences. 3. Write a subroutine that takes two filenames as its arguments and returns a nonzero value if the two files have identical contents. Return 0 if the files differ. 4. Write a subroutine that simulates the roll of a die (that is, it generates a random number between 1 and 6) and returns the number. COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 19

21 6.3 Solutions - Subroutines 1. One solution is: sub add_two { local ($arg1, $arg2) $result = $arg1 + $arg2; 2. Another solution is: sub count_t { local ($string) # There are a couple of tricks you can use to do this. # This one splits the string into words using "t" as # the split pattern. The number of occurrences of "t" # is one less than the number of words resulting from # the = split(/t/, $string); $retval - 1; 3. Another solution is: sub diff { local ($file1, $file2) # return false if we can't open a file return (0) unless open (FILE1, "$file1"); return (0) unless open (FILE2, "$file2"); while (1) { $line1 = <FILE1>; $line2 = <FILE2>; if ($line1 eq "") { $retval = ($line2 eq ""); last; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 20

22 if ($line2 eq "" $line1 ne $line2) { $retval = 0; last; # you should use close here, as this subroutine may # be called many times close (FILE1); close (FILE2); # ensure that the return value is the last evaluated # expression $retval; 4. One solution is: sub dieroll { $retval = int (rand(6)) + 1; COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 21

23 7 Associative Arrays 1. Write a program that reads lines of input consisting of two words per line, such as bananas 16 and creates an associative array from these lines. The first word is to be the subscript and the second word the value. 2. Write a program that reads a file and searches for lines of the form index word where word is a word to be indexed. Each indexed word is to be stored in an associative array, along with the line number on which it first occurs. Subsequent occurrences can be ignored. Print the resulting index. 3. Modify the program created in Exercise 2 to store every occurrence of each index line. Try building the associative array subscripts using the indexed word, a non-printable character, and a number. Print the resulting index. 4. Write a program that reads input lines consisting of a student name and five numbers representing the student's marks in English, history, mathematics, science, and geography, as follows: Jones Use an associative array to store these numbers in a database. Print out the names of all students with failing grades, grade less than 50, along with the subjects they failed. COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 22

24 7.1 Solutions - Associative Arrays 1. One solution is: while ($line = <STDIN>) { $line =~ s/^\s+ \s+$//g; ($subscript, $value) = split(/\s+/, $line); $array{$subscript = $value; 2. One solution is: $linenum = 0; while ($line = <STDIN>) { $linenum += 1; $line =~ s/^\s+ = split(/\s+/, $line); if ($words[0] eq "index" && $index{$words[1] eq "") { $index{$words[1] = $linenum; foreach $item (sort keys (%index)) { print ("$item: $index{$item\n"); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 23

25 3. One solution is: $linenum = 0; while ($line = <STDIN>) { $linenum += 1; $line =~ s/^\s+ = split(/\s+/, $line); # This program uses a trick: for each word, the array # item $index{"word" stores the number of occurrences # of that word. Each occurrence is stored in the # element $index{"word#n", where[]is a # positive integer. if ($words[0] eq "index") { if ($index{$words[1] eq "") { $index{$words[1] = 1; $occurrence = 1; else { $index{$words[1] += 1; $occurrence = $index{$words[1]; $index{$words[1]."#".$occurrence = $linenum; # The loop that prints the index takes advantage of the fact # that, when the list is sorted, the elements that count # occurrences are always processed just before the # corresponding elements that store occurrences. For example: # $index{word # $index{word#1 # $index{word#2 COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 24

26 foreach $item (sort keys (%index)) { if ($item =~ /#/) { print ("\n$item:"); else { print (" $index{$item"); print ("\n"); 4. One solution is: $student = = ("English", "history", "mathematics", "science", "geography"); while ($line = <STDIN>) { $line =~ s/^\s+ = split (/\s+/, = $words[0]; for ($count = 1; $count <= 5; $count++) { $marks{$words[0].$subjects[$count-1] = $words[$count]; # now print the failing grades, one student per line foreach $student (sort (@students)) { $has_failed = 0; foreach $subject (sort (@subjects)) { if ($marks{$student.$subject < 50) { if ($has_failed == 0) { $has_failed = 1; print ("$student failed:"); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 25

27 print (" $subject"); if ($has_failed == 1) { print ("\n"); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 26

28 8 Directories 1. Write a program that reads the directory /u/jqpublic and prints out all file and directory names that start with a period. Ignore the special files. (one period) and.. (two periods). 2. Write a program that lists all the files in the directory /u/jqpublic and then lists the contents of any subdirectories, their subdirectories, and so on. Use a recursive subroutine. 3. Write a program that uses readdir and rewinddir to read a directory named /u/jqpublic and print a sorted list of the files and directories in alphabetical order. Ignore all names beginning with a period. 4. Write a program that uses hot keys and does the following: Reads single digits and prints out their English-language equivalents. Terminates if it reads the Esc (escape) character. Ignores all other input. Prints out one English word per line. COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 27

29 8.1 Solutions - Directories 1. One solution is: opendir (MYDIR, "/u/jqpublic") die ("Can't open directory"); while ($file = readdir (MYDIR)) { next if ($file =~ /^\.{1,2$ ^[^.]/); print ("$file\n"); closedir (MYDIR); 2.One solution is: $filecount = 1; &print_dir ("/u/jqpublic"); sub print_dir { local ($dirname) local ($file, $subdir, $filevar); $filevar = "MYFILE". $filecount++; opendir ($filevar, $dirname) die ("Can't open directory"); # first pass: read and print file names print ("\ndirectory $dirname:\n"); while ($file = readdir ($filevar)) { next if ($file eq "." $file eq ".."); next if (-d ($dirname. "/". $file)); print ("$file\n"); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 28

30 # second pass: recursively print subdirectories rewinddir ($filevar); while ($subdir = readdir ($filevar)) { next unless (-d ($dirname. "/". $subdir)); next if ($subdir eq "." $subdir eq ".."); &print_dir ($dirname. "/". $subdir); closedir ($filevar); 3. One solution is: opendir (MYDIR, "/u/jqpublic") die ("Can't open directory"); # the following is a trick: "." is alphabetically less than # anything we want to print, so it makes a handy # initial value $lastfile = "."; until (1) { rewinddir (MYDIR); $currfile = ""; while ($file = readdir (MYDIR)) { next if ($file =~ /^\./); if ($file gt $lastfile && ($currfile eq "" $file lt $currfile)) { $currfile = $file; last if ($currfile eq ""); print ("$currfile\n"); $lastfile = $currfile; closedir (MYDIR); COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 29

31 4. One solution = ("zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"); &start_hot_keys; while (1) { $char = getc(stdin); last if ($char eq "\033"); next if ($char =~ /[^0-9]/); print ("$digits[$char]\n"); &end_hot_keys; sub start_hot_keys { system ("stty cbreak"); system ("stty -echo"); sub end_hot_keys { system ("stty -cbreak"); system ("stty echo"); D:\05_Courseware_2006\UNIX_Advanced\09_App_B_UNIX_Fundamentals_Advanced_Wo rkshop_qc.doc COMPUTER EDUCATION TECHNIQUES, INC. (UNIX-Fund: Level 2-6.5) App B: Page 30