View Category
Files
Reading

Read the contents of a file into a string

python
contents = open('myFile.txt', 'rt').read()
csharp
string contents = System.IO.File.ReadAllText("filename.txt");
clojure
(slurp "/tmp/foobar")

Process a file one line at a time

Open the source file to your solution and print each line in the file, prefixed by the line number, like:
1> First line of file
2> Second line of file
3> Third line of file
python
for no, line in enumerate(open(__file__)):
print "{0}> {1}".format(no+1, line.rstrip())
csharp
int counter = 0;

// If the file is large, you would want to buffer this instead of reading everything at once
foreach (string line in System.IO.File.ReadAllLines("filename.txt"))
{
Console.WriteLine("{0}> {1}", ++counter, line);
}
clojure
(defn read-line-by-line [fn]
(reduce str (map (partial format "%d> %s\n")
(iterate inc 1)
(read-lines fn))))
Writing

Write a string to a file

python
open('test.txt', 'wt').write('Hello World!')
csharp
System.IO.File.WriteAllText("filename.txt", "Some text to write to the file");
clojure
(with-out-writer "output.txt" (println "Hello file!"))

Append to a file

python
open('test.txt', 'at').write('Hello World!\n')
csharp
System.IO.File.AppendAllText("filename.txt", "Some text to append to the file");
clojure
(with-out-append-writer "output.txt" (println "This is appended to the file"))
Directories

Process each file in a directory

python
import os
results = (process(f) for f in os.listdir(".") if os.path.isfile(f))
csharp
foreach (string filename in System.IO.Directory.GetFiles(directory)) ProcessFile(filename);
clojure
; (defn process-file [f] "process one file" body...)
(map process-file (.listFiles (File. ".")))

Process each file in a directory recursively

python
import os
results = (process(os.path.join(p, n)) for p,d,l in os.walk(".") for n in l)
clojure
; (defn process-file [f] "process one file" body...)
(map process-file (file-seq (File. ".")))