Exercise: Renaming Files En Masse

This exercise will provide another (small) tool for your toolkit. This utility allows you to rename files given a directory name, a pattern to look for, and a pattern to change it to. For example, if a directory contains the filenames Chapter_01.rtf, Chapter_02.rtf, Chapter_04.rtf, and so on, you could rename all the files to Hour_01.rtf, Hour_02.rtf, Hour_04.rtf, and so on. This task normally isn't easy at a command prompt and just silly when you're using a GUI-based file browser.

Using your text editor, type the program from Listing 10.3 and save it as Renamer. Be sure to make the program executable according to the instructions you learned in Hour 1.

When you're done, try running the program by typing the following at a command line:

perl Renamer

Listing 10.4 shows some sample output from this program.

Listing 10.3 Complete Listing for Renamer

1:   #!/usr/bin/perl -w
2:
3:   use strict;
4:
5:   my($dir, $oldpat, $newpat);
6:   print "Directory: ";
7:   chomp($dir=<STDIN>);
8:   print "Old pattern: ";
9:   chomp($oldpat=<STDIN>);
10:  print "New pattern: ";
11:  chomp($newpat=<STDIN>);
12:
13:  opendir(DH, $dir) || die "Cannot open $dir: $!";
14:  my @files=readdir DH;
15:  close(DH);
16:  my $oldname;
17:  foreach(@files) {
18:      $oldname=$_;
19:      s/$oldpat/$newpat/;
20:      next if (-e "$dir/$_");
21:      if (! rename "$dir/$oldname", "$dir/$_") {
22:              warn "Could not rename $oldname to $_: $!"
23:      } else {
24:              print "File $oldname renamed to $_
";
25:      }
26:  }

Lines 13–15: The entries in the directory indicated by $dir are read into @files.

Lines 17–19: Each file from @files is assigned to $_ and that name is saved in $oldname. The original filename in $_ is then changed to the new name on line 19.

Line 20: Before renaming the file, this line makes sure the target filename doesn't already exist. Otherwise, the program could rename a file into an existing name—destroying the original data.

Lines 21–25: The file is renamed, and warnings are printed if the rename fails. Notice that the original directory name needs to be appended onto the filenames—for example, $dir/$oldname—because @files doesn't contain full pathnames, which you need for the rename.

Listing 10.4 Sample Output from Renamer

1:   Directory: /tmp
2:   Old Pattern: Chapter
3:   New Pattern: Hour
4:   File Chapter_02.rtf renamed to Hour_02.rtf
5:   File Chapter_10.rtf renamed to Hour_10.rtf