Importance of Forking in Unix
Forking is an important part of Unix, critical to the support of its design philosophy, which encourages the development of filters. In Unix, a filter is a (usually small) program that reads its input from stdin, and writes its output to stdout. A pipeline of these commands can be strung together by a shell to create new commands. For example, one can string together the output of the find(1)
command and the input of the wc(1)
command to create a new command that will print a count of files ending in ".cpp" found in the current directory and any subdirectories, as follows:
In order to accomplish this, the shell forks itself, and uses pipes, a form of interprocess communication, to tie the output of the find
command to the input of the wc
command. First, a pipe is created at two fresh file descriptors, and then two child processes are created, one for each command (find
and wc
). Each child process first dup2(2)
s the appropriate pipe file descriptor to either its standard input or output. Then these child processes overlay themselves with the code associated with the programs they are intended to execute, using the exec(3)
family of system calls.
More generally, forking is also performed by the shell each time a user issues a command. A child process is created by forking the shell, and the child process is overlaid, once again by exec
, with the code associated with the program to be executed.
Read more about this topic: Fork (operating System)
Famous quotes containing the words importance of and/or importance:
“In my public statements I have earnestly urged that there rested upon government many responsibilities which affect the moral and spiritual welfare of our people. The participation of women in elections has produced a keener realization of the importance of these questions and has contributed to higher national ideals. Moreover, it is through them that our national ideals are ingrained in our children.”
—Herbert Hoover (18741964)
“In the United States all business not transacted over the telephone is accomplished in conjunction with alcohol or food, often under conditions of advanced intoxication. This is a fact of the utmost importance for the visitor of limited funds ... for it means that the most expensive restaurants are, with rare exceptions, the worst.”
—John Kenneth Galbraith (b. 1908)