Ruby Cookbook

Recipe 6.1. Checking to See If a File Exists Problem Given a filename, you want to see whether the corresponding file exists and is the right kind for your purposes. Solution Most of the time you'll use the File.file? predicate, which ret...

Recipe 6.2. Checking Your Access to a File Problem You want to see what you can do with a file: whether you have read, write, or (on Unix systems) execute permission on it. Solution Use the class methods File.readable?, File.write...

Recipe 6.3. Changing the Permissions on a File Problem You want to control access to a file by modifying its Unix permissions. For instance, you want to make it so that everyone on your system can read a file, but only you can write to it. ...

Recipe 6.4. Seeing When a File Was Last Used Problem Problem You want to see when a file was last accessed or modified. Solution The result of File.stat contains a treasure trove of metadata about a file. Perhaps the most use...

Recipe 6.5. Listing a Directory Problem You want to list or process the files or subdirectories within a directory. Solution If you're starting from a directory name, you can use Dir.entries to get an array of the items in the dir...

Recipe 6.6. Reading the Contents of a File Problem You want to read some or all of a file into memory. Solution Open the file with Kernel#open, and pass in a code block that does the actual reading. To read the entire file into a ...

Recipe 6.7. Writing to a File Problem You want to write some text or Ruby data structures to a file. The file might or might not exist. If it does exist, you might want to overwrite the old contents, or just append new data to the end of t...

Recipe 6.8. Writing to a Temporary File Problem You want to write data to a secure temporary file with a unique name. Solution Create a Tempfile object. It has all the methods of a File object, and it will be in a location...

Recipe 6.9. Picking a Random Line from a File Problem You want to choose a random line from a file, without loading the entire file into memory. Solution Iterate over the file, giving each line a chance to be the randomly selected one: ...

Recipe 6.10. Comparing Two Files Problem You want to see if two files contain the same data. If they differ, you might want to represent the differences between them as a string: a patch from one to the other. Solution If two files d...

Recipe 6.11. Performing Random Access on "Read-Once" Input Streams Problem You have an IO object, probably a socket, that doesn't support random-access methods like seek, pos=, and rewind. You want to treat this object like a file on disk,...

Recipe 6.12. Walking a Directory Tree Problem You want to recursively process every subdirectory and file within a certain directory. Solution Suppose that the directory tree you want to walk looks like this (see this chapter's introdu...

Recipe 6.13. Locking a File Problem You want to prevent other threads or processes from modifying a file that you're working on. Solution Open the file, then lock it with File#flock. There are two kinds of lock; pass in the File c...

Recipe 6.14. Backing Up to Versioned Filenames Problem You want to copy a file to a numbered backup before overwriting the original file. More generally: rather than overwriting an existing file, you want to use a new file whose name ...

Recipe 6.15. Pretending a String Is a File Problem You want to call code that expects to read from an open file object, but your source is a string in memory. Alternatively, you want to call code that writes its output to a file, but have it ac...

Recipe 6.16. Redirecting Standard Input or Output Problem You don't want the standard input, output, or error of your process to go to the default IO objects set up by the Ruby interpreter. You want them to go to other filetype objec...

Recipe 6.17. Processing a Binary File Problem You want to read binary data from a file, or write it to one. Solution Since Ruby strings make no distinction between binary and text data, processing a binary file needn't be any differe...

Recipe 6.18. Deleting a File Problem You want to delete a single file, or a whole directory tree. Solution Removing a file is simple, with File.delete: import 'fileutils' FileUtils.touch "doomed_file" File.exists? "doomed_fil...

Recipe 6.19. Truncating a File Problem You want to truncate a file to a certain length, probably zero bytes. Solution Usually, you want to destroy the old contents of a file and start over. Opening a file for write access will automa...

Recipe 6.20. Finding the Files You Want Problem You want to locate all the files in a directory hierarchy that match some criteria. For instance, you might want to find all the empty files, all the MP3 files, or all the files named "README." ...