In this post I’ll show some F# constructs, all put together in a simple application that modifies file names that match a criteria. This would be an application that is started from a console with the following command line options:<\/p>\n
\r\nfilesmod.exe -f < folder > [-r] -p < pattern > [-pre < prefix >] [-suf < suffix >]\r\n -f < folder> specifies the folder where the files are located\r\n -r indicates that the specified folder should be parsed\r\n recursively\r\n -p < pattern> indicates a pattern used for filtering files\r\n -pre < prefix> indicats a prefix to the added to all files\r\n that match the criteria\r\n -suf < suffix> indicats a suffix to the added to all files\r\n that match the criteria\r\n<\/pre>\nReading command line<\/h3>\n
The command line arguments can be retrieved using the Environment class from the .NET framework. This class has a static method called GetCommandLineArgs() that returns a list of the passed arguments.
\nWe can define a type that contains all the parsed arguments.<\/p>\n\r\ntype CommandOptions =\r\n { mutable Folder : string;\r\n mutable Recursive : bool;\r\n mutable Pattern : string;\r\n mutable Prefix : string;\r\n mutable Suffix : string;}\r\n<\/pre>\nThis mutable record can be instantiated, and the value can be mutated while parsing the arguments. This is how you instantiate it:<\/p>\n
\r\n let cmdops =\r\n { new CommandOptions\r\n with Folder = String.Empty\r\n and Recursive = false\r\n and Pattern = String.Empty\r\n and Prefix = String.Empty\r\n and Suffix = String.Empty }\r\n<\/pre>\nParsing the command line arguments can be done with pattern matching. This is the equivalent of switches in C+\/C#\/Java, only more powerful.
\nBasically, I’m checking each argument, and if it’s a flag in the command line (-f, -r, -p, -pre, -sub) I take the next argument and put it in the appropriate property of the record.<\/p>\n\r\n try\r\n let args = Environment.GetCommandLineArgs()\r\n for i = 0 to args.Length-1 do\r\n match args.(i) with\r\n | \"-f\" when i+1 <= args.Length-1 -> cmdops.Folder <- args.(i+1)\r\n | \"-r\" -> cmdops.Recursive <- true\r\n | \"-p\" when i+1 <= args.Length-1 -> cmdops.Pattern <- args.(i+1)\r\n | \"-pre\" when i+1 <= args.Length-1 -> cmdops.Prefix <- args.(i+1)\r\n | \"-suf\" when i+1 <= args.Length-1 -> cmdops.Suffix <- args.(i+1)\r\n | _ -> ()\r\n done\r\n with e -> printfn \"%s\" e.Message\r\n<\/pre>\nThere are two things you could notice here. The first is the try … with block that makes sure any possible exception is caught.
\nThe second is the quarding the rules with the contidion that the current argument is not the last one in the list. (-f should be followed by a folder, -suf by a suffix, etc.)
\nYou can see what in the when statement:<\/p>\n\r\nwhen i+1 <= args.Length-1\r\n<\/pre>\nGetting the files in a directory<\/h3>\n
We can get all files in a folder, using the following algorithm:<\/p>\n
That is spelled “recursion”!. Our function should take several arguments: the path of a folder, a pattern for mathing filenames and a flag indicating whether sub-folders should be parsed or not.<\/p>\n
\r\nlet rec allFiles dir pattern r =\r\n seq\r\n { for file in Directory.GetFiles(dir, pattern) do\r\n yield file\r\n if r then\r\n for subdir in Directory.GetDirectories(dir) do\r\n for file in allFiles subdir pattern r do\r\n yield file }\r\n<\/pre>\nThe above function is recursive and returns a sequence of file names. Sequences are lazy, which means that successive elements are computed and returned on demand, when they are needed.
\nThat is the opposite of a list or array, whose elements are created at once. The keyword ‘yield’ here is used to return a new value as the sequence is iterated.<\/p>\n
Processing the files<\/h3>\n
To process the files, we simply iterate over the sequence of files from the specified folder, match it against the provided parttern, and if there is a match, apply the prefix and\/or suffix transformation.<\/p>\n
\r\n for name in (allFiles cmdops.Folder \"*.*\" cmdops.Recursive) do\r\n let file = new FileInfo(name)\r\n if(Regex.IsMatch(file.Name, cmdops.Pattern, RegexOptions.Singleline)) then\r\n let filename = file.Name.Substring(0, file.Name.LastIndexOf('.'))\r\n let newname = file.Directory.FullName+\"\\\\\"+cmdops.Prefix+filename+cmdops.Suffix+file.Extension\r\n System.IO.File.Move(file.FullName, newname)\r\n printfn \"%s -> %s\" file.FullName newname\r\n done\r\n<\/pre>\nWell, I have two cores on my machine, and since the Parallel FX framework is available, I like to use it. So here is the parallel version of that:<\/p>\n
\r\n try\r\n Parallel.ForEach(allFiles cmdops.Folder \"*.*\" cmdops.Recursive, fun name ->\r\n let file = new FileInfo(name)\r\n if(Regex.IsMatch(file.Name, cmdops.Pattern, RegexOptions.Singleline)) then\r\n let filename = file.Name.Substring(0, file.Name.LastIndexOf('.'))\r\n let newname = file.Directory.FullName+\"\\\\\"+cmdops.Prefix+filename+cmdops.Suffix+file.Extension\r\n System.IO.File.Move(file.FullName, newname)\r\n printfn \"%s -> %s\" file.FullName newname)\r\n with e -> printfn \"%s\" e.InnerException.Message\r\n<\/pre>\nThe provided (via command line) pattern is a regular expression. Initially, the folder is checked for all files and then these files are matched against this regular expression.<\/p>\n
As I was saying in a previous post, if you use PFX, you have to add a reference to the System.threading.dll assembly, which requires a reference to the System.Core.dll assembly.
\nThat should be specified at the project’s propertyes.<\/p>\n
\n-r C:\\WINDOWS\\assembly\\GAC_MSIL\\System.Core\\3.5.0.0__b77a5c561934e089\\System.Core.dll -r “C:\\Program Files\\Microsoft Parallel Extensions Dec07 CTP\\System.Threading.dll”\n<\/p><\/blockquote>\n
Putting all together<\/h3>\n
All that put together looks like this:<\/p>\n
\r\n#light\r\n\r\nopen System\r\nopen System.IO\r\nopen System.Text.RegularExpressions\r\n\r\nopen System.Threading\r\n\r\nlet rec allFiles dir pattern r =\r\n seq\r\n { for file in Directory.GetFiles(dir, pattern) do\r\n yield file\r\n if r then\r\n for subdir in Directory.GetDirectories(dir) do\r\n for file in allFiles subdir pattern r do\r\n yield file }\r\n\r\nlet showUsage() =\r\n printfn \"filesmod.exe -f < folder > [-r] -p < pattern > [-pre < prefix >] [-suf < suffix >]\"\r\n printfn \" -f < folder >\\tspecifies the folder where the files are located\"\r\n printfn \" -r\\t\\tindicates that the specified folder should be parsed\\n\\t\\trecursively\"\r\n printfn \" -p < pattern >\\tindicates a pattern used for filtering files\"\r\n printfn \" -pre < prefix >\\tindicats a prefix to the added to all files\\n\\t\\tthat match the criteria\"\r\n printfn \" -suf < suffix >\\tindicats a suffix to the added to all files\\n\\t\\tthat match the criteria\"\r\n\r\ntype CommandOptions =\r\n { mutable Folder : string;\r\n mutable Recursive : bool;\r\n mutable Pattern : string;\r\n mutable Prefix : string;\r\n mutable Suffix : string;}\r\n\r\nlet main()=\r\n let cmdops =\r\n { new CommandOptions\r\n with Folder = String.Empty\r\n and Recursive = false\r\n and Pattern = String.Empty\r\n and Prefix = String.Empty\r\n and Suffix = String.Empty }\r\n \r\n try\r\n let args = Environment.GetCommandLineArgs()\r\n for i = 0 to args.Length-1 do\r\n match args.(i) with\r\n | \"-f\" when i+1 <= args.Length-1 -> cmdops.Folder <- args.(i+1)\r\n | \"-r\" -> cmdops.Recursive <- true\r\n | \"-p\" when i+1 <= args.Length-1 -> cmdops.Pattern <- args.(i+1)\r\n | \"-pre\" when i+1 <= args.Length-1 -> cmdops.Prefix <- args.(i+1)\r\n | \"-suf\" when i+1 <= args.Length-1 -> cmdops.Suffix <- args.(i+1)\r\n | _ -> ()\r\n done\r\n with e -> printfn \"%s\" e.Message\r\n\r\n if ((String.IsNullOrEmpty(cmdops.Prefix) && String.IsNullOrEmpty(cmdops.Suffix)) || \r\n String.IsNullOrEmpty(cmdops.Pattern) || \r\n String.IsNullOrEmpty(cmdops.Folder)) then\r\n showUsage()\r\n else\r\n try\r\n Parallel.ForEach(allFiles cmdops.Folder \"*.*\" cmdops.Recursive, fun name ->\r\n let file = new FileInfo(name)\r\n if(Regex.IsMatch(file.Name, cmdops.Pattern, RegexOptions.Singleline)) then\r\n let filename = file.Name.Substring(0, file.Name.LastIndexOf('.'))\r\n let newname = file.Directory.FullName+\"\\\\\"+cmdops.Prefix+filename+cmdops.Suffix+file.Extension\r\n System.IO.File.Move(file.FullName, newname)\r\n printfn \"%s -> %s\" file.FullName newname)\r\n with e -> printfn \"%s\" e.InnerException.Message\r\n \r\n Console.WriteLine(\"Press any key to continue...\")\r\n Console.ReadKey()\r\n \r\nmain()\r\n<\/pre>\nOf course, the options available in this application (on file name changes) are pretty limited, but that can be extended at will.<\/p>\n","protected":false},"excerpt":{"rendered":"
In this post I’ll show some F# constructs, all put together in a simple application that modifies file names that match a criteria. This would be an application that is started from a console with the following command line options: filesmod.exe -f < folder > [-r] -p < pattern > [-pre < prefix >] [-suf … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[37,42],"tags":[43,47,46,45,44,48],"class_list":["post-121","post","type-post","status-publish","format-standard","hentry","category-fsharp","category-parallel-programming","tag-files","tag-parallel","tag-pattern","tag-record","tag-recursive","tag-regex"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t