Reading and Writing Files
Let's discuss what happens under the hood when a call to read or write is made.
We'll cover the following...
Once we have some files, of course, we might like to read or write them. Let’s start by reading an existing file. If we were typing at a command line, we might just use the program cat to dump the contents of the file to the screen.
prompt> echo hello > fooprompt> cat foohelloprompt>
Try it out yourself:
In this code snippet, we redirect the output of the program echo to the file foo, which then contains the word “hello” in it. We then use cat to see the contents of the file. But how does the cat program access the file foo?
Strace to trace cat
To find this out, we’ll use an incredibly useful tool to trace the system calls made by a program. On Linux, the tool is called strace; other systems have similar tools (see dtruss on a Mac, or truss on some older UNIX variants). What strace does is trace every system call made by a program while it runs, and dump the trace to the ...