1. Perl File and Directory Access Software Tools

2. Slide 2 Changing Directories You can change the current working directory within Perl, just like the cd shell command. In Perl, the chdir function, takes a single argument -- the directory name to change to. chdir returns true if you’ve successfully changed to the requested directory, and false if you could not. chdir("/etc") || die "cannot cd to /etc";

3. Slide 3 Changing Directories l Like other functions, parentheses are optional: $ cat cd1 #!/usr/local/bin/perl5 -w print "where to go? "; chomp($where = ); if(chdir $where){ print "chdir succeeded, now in $where\n"; }else{ print "chdir did not succeeded\n"; } $ cd1 where to go? /bin chdir succeeded, now in /bin $

4. Slide 4 Changing Directories l When your Perl program starts, the current working directory will be inherited from the shell that invoked it. However, using chdir in Perl will not change the working directory of the shell when your program ends. The chdir function without a parameter defaults to taking you to your home directory.

5. Slide 5 Globbing The shell takes a * and turns it into a list of all the filenames in the current directory. Similarly, [a-m]*.cpp turns into a list of all filenames in the current directory that begin with a letter in the first half of the alphabet, and end in.cpp. The expansion of * or /etc/host* into the list of matching filenames is called globbing.

6. Slide 6 Globbing l Perl supports globbing. Just put the globbing pattern between angle brackets or use the glob function: @all = ; @b = ; @c = glob("[a-m]*.cpp");# same as @b l In a list context, the glob returns a list of all names that match the pattern (or an empty list if none match).

7. Slide 7 Globbing l Example: $ ls addressletter1namessort $ cat glob1 #!/usr/local/bin/perl5 -w @files = ; foreach $file (@files){ print "$file\n"; } $ glob1 address letter1 $

8. Slide 8 Globbing l If you use a full pathname in your glob, you will get full pathnames as a result: $ cat glob2 #!/usr/local/bin/perl5 -w @files = ; foreach $file (@files){ print "$file "; } print "\n"; $ glob2 /etc/hostname.le0 /etc/hosts /etc/hosts.allow /etc/hosts.deny $

9. Slide 9 Globbing l If you want just the simple filename, you can use substitute to chop off the directory part of the string: $ cat glob3 #!/usr/local/bin/perl5 -w @files = ; foreach $file (@files){ $file =~ s#.*/##;# delete to last slash print "$file "; } print "\n"; $ glob3 hostname.le0 hosts hosts.allow hosts.deny $

10. Slide 10 Globbing l Multiple patterns are permitted inside the glob: @bill_files = ; l The argument to glob is variable interpolated: $ cat glob4 #!/usr/local/bin/perl5 -w if(-d "/homes/horner/111"){ $where = "/homes/horner/111"; }else{ $where = "/homes/horner"; } @files = ; print "@files\n"; $ glob4 /homes/horner/111/letter1 /homes/horner/111/names

11. Slide 11 Removing a File The Perl unlink function deletes a file, exactly like the UNIX rm command. unlink("bill");# bye bye bill l Example: $ ls letter1namesunlink1 $ cat unlink1 #!/usr/local/bin/perl5 -w print "what file to delete? "; chomp($what = ); unlink($what); $ unlink1 what file to delete? letter1 $ ls namesunlink1 $

12. Slide 12 Removing a File unlink can take a list of names as well: unlink("bill", "gates"); unlink ;# delete all.cpp files The return value on unlink is the number of files successfully deleted. foreach $file ( ){ if(unlink($file) == 0){ print "trouble deleting $file\n"; }

13. Slide 13 Removing a File With no arguments to unlink, $_ is used as the default. foreach ( ){ if(unlink == 0){ print "trouble deleting $_\n"; }

14. Slide 14 Renaming a File The Perl function rename allows you to rename files. Here is how to rename the file gates into cheap : rename("gates", "cheap"); rename returns a true value if successful. if(rename("gates", "cheap")){ print "Bill is now cheap\n"; }else{ print "Bill is still gates\n"; }

15. Slide 15 Hard Links The Perl function link allows you to create a hard link. Here is how to link from the file gates to cheap : link("gates", "cheap"); link returns true if successful. if(link("gates", "cheap")){ print "Bill is now also cheap\n"; }else{ print "Bill is still only gates\n"; }

16. Slide 16 Soft Links The Perl function symlink allows you to create a soft (symbolic) link. Here is how to symbolic link from gates to cheap : symlink("gates", "cheap"); readlink returns the name pointed at by the specified symbolic link: symlink("gates", "cheap"); $x = readlink("cheap"); print "cheap points at $x\n";#cheap points at gates

17. Slide 17 Making and Removing Directories The Perl functions mkdir and rmdir allow you to make and remove directories. mkdir takes the name of the new directory and a mode that determines the permissions Use 0755 for the mode to allow user full (rwx) permission, and no write permission for group and other (rx only). mkdir("gatesdir", 0755); rmdir("gatesdir");

18. Slide 18 Permissions The leading mode number is always 0, and the other 3 numbers are permissions for user, group, and other respectively. l The mode values are octal, and have the following meanings: 0 --- 1 --x 2 -w- 3 -wx 4 r-- 5 r-x 6 rw- 7 rwx

19. Slide 19 Modifying Permissions The Perl function chmod allows you to change file and directory permissions: mkdir("gatesdir", 0755); #u:rwx g:rx o:rx chmod(0750, "gatesdir"); #u:rwx g:rx o: chmod(0531, "gates"); #u:rx g:wx o:x chmod(0642, "gates", "cheap"); #u:rw g:r o:w