write (system call)

The write is one of the most basic routines provided by a Unix-like operating system kernel. It writes data from a buffer declared by the user to a given device, such as a file. This is the primary way to output data from a program by directly using a system call. The destination is identified by a numeric code. The data to be written, for instance a piece of text, is defined by a pointer and a size, given in number of bytes.

write thus takes three arguments:

1. The file code (file descriptor or fd).
2. The pointer to a buffer where the data is stored (buf).
3. The number of bytes to write from the buffer (nbytes).