Ahmed Ben Bella, Algeria's...

...first elected president, died at age 93. He has an interesting obit in the Times, but it was this paragraph that caught my attention (my emphasis): 

In 1949, Mr. Ben Bella helped rob a post office in Oran, Algeria. Tracked down, he was sentenced to a long stint in the Blida prison. In 1952, with the aid of a file hidden in a loaf of bread, he broke out and went to Cairo, where he became one of the liberation movement’s nine top leaders. 

Really? A file? I thought that only happened in the movies. How long would it take to file through the bars of a jail cell? That would have to be either a heck of a file or some pretty crummy bars. Who supplied those, the warden's brother-in-law?