1. 2000 Copyrights, Danielle S. Lahmani Foreach example Example: @numbers = ( 3, 5, 7, 9) foreach $one (@numbers ) { $one*=3; } # @numbers is now (9,15,21,27)

2. 2000 Copyrights, Danielle S. Lahmani PERL: HASHES A hash is a collection of scalar data with individual elements selected by some index.  Index values are arbitrary scalars called keys; They are used to retrieve values from the array.  Elements of a hash have no special order  A hash is denoted by "%" sign  Elements of a hash are referenced by $hashname{key}

3. 2000 Copyrights, Danielle S. Lahmani HASH: Examples Example: %carcolor = ("buick", "yellow"); $mycolor = $carcolor{ "buick"}; $mycolor is now "yellow" %copy = %original; # copy from %original to %copy

4. 2000 Copyrights, Danielle S. Lahmani HASH FUNCTIONS keys functions: keys(%hashname) yields a list of the current keys in the hash %hashname. Example: keys(%hashname) = keys %hashname; # once for each key of % fred foreach $key (keys (%fred)) { print "at $key we have $fred{$key} \n"; # show key and value

5. 2000 Copyrights, Danielle S. Lahmani HASH FUNCTIONS (CONT') values function: values(%hashname) yields a list of the current valuesof %hashname in the same order as keys returned by keys(%hashname) %lastname = ("barney", "flinstone", "gerry", "smith"); @lastname = values(%lastname); #grab the values

6. 2000 Copyrights, Danielle S. Lahmani HASH FUNCTIONS (each)  each function: each(%hashname) returns a key-value pair as a two element list. Used to iterate over an entire hash (examining every element of ). Example: while (($first, $last)) = each(%lastname)) { print "the last name of $first is $last\n"; }

7. 2000 Copyrights, Danielle S. Lahmani Hash function: delete removes hash elements, takes a hash reference as argument delete $lastname{"barney"}; #lastname has only one key-value pair now.

8. 2000 Copyrights, Danielle S. Lahmani CONTROL STRUCTURES  Perl supports "if", "for" while" similar than those in C.  "foreach" constructs is from the C shell foreach example: –If the list we are iterating over is made of real variables Rather than some functions returning a list value, –Then the variable being used for iteration is in fact An alias for each variable in the list instead of being A merely copy of the values

9. 2000 Copyrights, Danielle S. Lahmani BASIC I/O  Input from STDIN Perl uses the variable $_ to contain the line read from STDIN. $a = ;#reads the next line @a = ;# reads all lines until control ^D typically while (defined ($line = ) { # process $line here } when no more lines read. returns undef.

10. 2000 Copyrights, Danielle S. Lahmani using the diamond operator <>  <> operates like, but gets data from file or files specified on the command line that invoked the PERL program. <> looks at the @ARGV array #!/usr/bin/perl while (<>) { print $_; }

11. 2000 Copyrights, Danielle S. Lahmani Output to STDOUT print for normal output printf for formatted output

12. 2000 Copyrights, Danielle S. Lahmani REGULAR EXPRESSIONS  PERL supports the same regular expressions as in SED.  =~ match operator It takes a regular expression operator on the right side and changes the target of the operator to some value. The target of the =~ operator can be any expression that yields some scalar string value. Example: if ( = ~ /^[yY]/) { print" what can I do for you? ";

13. 2000 Copyrights, Danielle S. Lahmani Regular expressions: split function split function takes a regular expression and a string, and looks for all occurrences of the regular expression withinthat string. Parts of the string that don't match the regular expression are returned in sequence as a list of values

14. 2000 Copyrights, Danielle S. Lahmani Example of split function $line = "merlyn::118:120:Randal:/home/merlyn:/usr/bi n/perl"; @fields = split(/:/, $line); # split $line, using : as delimiter # now @fields is ("merlyn,"", "118", "120", "Randal", #"/home/merlyn", "/usr/bin/perl")

15. 2000 Copyrights, Danielle S. Lahmani join function takes a list of values and glues them together with a glue string between each list element. Example: $outline = join(":", @fields);

16. 2000 Copyrights, Danielle S. Lahmani PERL : FUNCTIONS Defining a user function Sub subname { Statement_1; Statement_2; Statement_3; }  return value is the value of the return statement or of the last expression evaluated in the subroutine.

17. 2000 Copyrights, Danielle S. Lahmani Function Arguments Subroutine invocation is followed by a list within parenthesis Causing the list to be automatically assigned to a special variable named @_ for the duration of the subroutine. $_[0] is the 1 st element of the @_ array @_ variable is private to the subroutine.

18. 2000 Copyrights, Danielle S. Lahmani Function private variables using the my operator sub add { my ($sum);#make $sum a local variable foreach $_ ( @_) { $sum += $_;# add each element } return $sum #last expression evaluated }

19. 2000 Copyrights, Danielle S. Lahmani Functions: Semi-private variables  semi-private variables using local local variables are visible to functions called from within the block in which those variables are declared.

20. 2000 Copyrights, Danielle S. Lahmani FILEHANDLES Recommendation use all uppercase letters in your filehandles. 3 files handles, STDIN, STDOUT, STDERR for standard in, out and error. open(FILEHANDLE, "filename"); >"filename" >> "filename” die: equivalent to "open that file or die." open(FILEHANDLE,>"filename") | | die "Sorry could not create filename\n"; Perl provides -op file tests just like the shells.

21. 2000 Copyrights, Danielle S. Lahmani Perl modules TBD

22. 2000 Copyrights, Danielle S. Lahmani USER DATABASE MANIPULATION Most UNIX systems have a standard library called DBM, Which allows programs to store a collection of key-value pairs Into a pair of disk files. In Perl, a hash may be associated with a DBM through a process Similar to opening a file. dbmopen function associates a DBM database with a DBM array:

23. 2000 Copyrights, Danielle S. Lahmani Database interface example dbmopen(%ARRAYNAME, "dbmfilename", $mode); dbmopen(%FRED,."mydatabase", 0644); delete $FRED{"barney"} while (($key, $value) = each(%FRED)) { print "$key has value of $value\n"; }

24. 2000 Copyrights, Danielle S. Lahmani perl debugging perl -d h print out a help message T stack trace s insgle step n next f finish c continue q quit D delete all breakpoints

25. 2000 Copyrights, Danielle S. Lahmani SYSTEM CALLS Perl provides an interface to many UNIX system calls. Interface is via Perl functions, not directly through the system call library. The interface use is dependent on the implementation and version of Perl being used.