Data.Conduit.Find

Introduction

• *find-conduit** is essentially a souped version of GNU find for Haskell, using a DSL to provide both ease of us, and extensive flexbility.

In its simplest form, let's compare some uses of find to find-conduit. Bear in mind that the result of the find function is a conduit, so you're expected to either sink it to a list, or operate on the file paths as they are yielded.

Basic comparison with GNU find

A typical find command:

find src -name '*.hs' -type f -print

Would in find-conduit be:

find src (glob "*.hs" <> regular) $$ mapM_C (liftIO . print)

The glob predicate matches the file basename against the globbing pattern, while the regular predicate matches plain files.

A more complicated example:

find . -size +100M -perm 644 -mtime 1

Now in find-conduit:

let megs = 1024 * 1024
    days = 86400
now <- liftIO getCurrentTime
find "." ( fileSize (> 100*megs)
        <> hasMode 0o644
        <> lastModified (> addUTCTime now (-(1*days)))
         )

Appending predicates like this expressing an and relationship. Use <|> to express or. You can also negate any predicate:

find "." (not_ (hasMode 0o644))

By default, predicates, whether matching or not, will allow recursion into directories. In order to express that matching predicate should disallow recursion, use prune:

find "." (prune (depth (> 2)))

This is the same as using '-maxdepth 2' in find.

find "." (prune (filename_ (== "dist")))

This is the same as:

find . \( -name dist -prune \) -o -print

Performance

find-conduit strives to make file-finding a well performing operation. To this end, a composed Predicate will only call stat once per entry being considered; and if you prune a directory, it is not traversed at all.

By default, find calls stat for every file before it applies the predicate, in order to ensure that only one such call is needed. Sometimes, however, you know just from the FilePath that you don't want to consider a certain file, or you want to prune a directory tree.

To support these types of optimized queries, a variant of find is provided called findWithPreFilter. This takes two predicates: one that is applied to only the FilePath, before stat (or lstat) is called; and one that is applied to the full file information after the stat.

Other notes

See Cond for more details on the Monad used to build predicates.

Finding functions

find :: (MonadIO m, MonadResource m) => FilePath -> Predicate m FileEntry -> Source m FilePath

find' :: (MonadIO m, MonadResource m) => FilePath -> Predicate m FileEntry -> Source m FileEntry

lfind :: (MonadIO m, MonadResource m) => FilePath -> Predicate m FileEntry -> Source m FilePath

lfind' :: (MonadIO m, MonadResource m) => FilePath -> Predicate m FileEntry -> Source m FileEntry

stat :: MonadIO m => Predicate m FileEntry

lstat :: MonadIO m => Predicate m FileEntry

test :: MonadIO m => Predicate m FileEntry -> FilePath -> m Bool

Test a file path using the same type of Predicate that is accepted by find.

findRaw :: (MonadIO m, MonadResource m) => FilePath -> Bool -> Predicate m FileEntry -> Source m FileEntry

A raw find does no processing on the FileEntry, leaving it up to the user to determine when and if stat should be called. Note that unless you take care to indicate when recursion should happen, an error will result when the raw finder attempts to recurse on a non-directory. The bare minimum for a proper finder should look like this for non-recursion:

 findRaw <path> $ do
     <apply predicates needing only pathname or depth>
     localM stat $ do
         directory ||: norecurse
         <apply predicates needing stat info>

To apply predicates only to a single directory, without recursing, simply start (or end) the predicate with norecurse, and use localM stat or localM lstat at the point where you need FileStatus information.

File path predicates

ignoreVcs :: Monad m => Predicate m FileEntry

Return all entries, except for those within version-control metadata directories (and not including the version control directory itself either).

regex :: Monad m => Text -> Predicate m FileEntry

glob :: Monad m => Text -> Predicate m FileEntry

Find every entry whose filename part matching the given filename globbing expression. For example: glob *.hs.

filename_ :: Monad m => (FilePath -> Bool) -> Predicate m FileEntry

filenameS_ :: Monad m => (String -> Bool) -> Predicate m FileEntry

filepath_ :: Monad m => (FilePath -> Bool) -> Predicate m FileEntry

filepathS_ :: Monad m => (String -> Bool) -> Predicate m FileEntry

withPath :: Monad m => (FilePath -> m Bool) -> Predicate m FileEntry

File entry predicates (uses stat information)

regular :: Monad m => Predicate m FileEntry

hasMode :: Monad m => FileMode -> Predicate m FileEntry

executable :: Monad m => Predicate m FileEntry

depth :: Monad m => (Int -> Bool) -> Predicate m FileEntry

lastAccessed :: Monad m => (UTCTime -> Bool) -> Predicate m FileEntry

lastModified :: Monad m => (UTCTime -> Bool) -> Predicate m FileEntry

withFileStatus :: Monad m => (FileStatus -> m Bool) -> Predicate m FileEntry

Predicate combinators

(=~) :: FilePath -> Text -> Bool

This is a re-export of =~, with the types changed for ease of use with this module. For example, you can simply say:

    filename_ (=~ "\\.hs$")

Which is the same thing as:

    regex "\\.hs$"

Types and type classes

data FileEntry

Constructors

FileEntry

Fields

entryPath :: FilePath

entryDepth :: Int

entryStatus :: Maybe FileStatus

This is Nothing until we determine stat should be called.

Instances

Show FileEntry