Recover deleted text files on Linux

$ grep -a -B 25 -A 100 'some string in the file' /dev/sda1 > results.txt

Explanation:

Grep searches through a file and prints out all the lines that match some pattern. Here, the pattern is some string that is known to be in the deleted file. The more specific this string can be, the better. The file being searched by grep (/dev/sda1) is the partition of the hard drive the deleted file used to reside in. The “-a” flag tells grep to treat the hard drive partition, which is actually a binary file, as text. Since recovering the entire file would be nice instead of just the lines that are already known, context control is used. The flags “-B 25 -A 100” tell grep to print out 25 lines before a match and 100 lines after a match. Be conservative with estimates on these numbers to ensure the entire file is included (when in doubt, guess bigger numbers). Excess data is easy to trim out of results, but if you find yourself with a truncated or incomplete file, you need to do this all over again. Finally, the ”> results.txt” instructs the computer to store the output of grep in a file called results.txt.

Source: http://spin.atomicobject.com/2010/08/18/undelete by Andrew Bellenir