Review
•UNIX file system
–File system abstraction
–Directories
–File descriptors
•Unix API Programming Examples and Techniques
–Example with direct IO
•open, close, fdopen, lseek, unlink
–Variable argument list
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UNIX File I/O and Pipes: File Descriptors, open(), pipe(), and Implementation in Shell, Slides of Computer Programming
A review of unix file i/o concepts, focusing on file descriptors, open() system call, and pipe() system call. It also covers the implementation of pipes in a shell. Examples and exercises to help understand the concepts.
Typology: Slides
2012/2013
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Review
- UNIX file system
- File system abstraction
- Directories
- File descriptors
- Unix API Programming Examples and Techniques
- Example with direct IO
- open, close, fdopen, lseek, unlink
- Variable argument list
- Example with direct IO
Review
- File I/O
- File descriptors
- open, creat, close, dup, dup
- I/O redirection
- File descriptors
- Process management
- fork, exit, wait, waitpid, execv
- Pipes
- Named and unnamed pipes
- Implementing pipe in a shell
Pipes
• Named pipe ( not our emphasis )
• Unnamed pipe
• Implementing pipe in a shell
Named and unnamed pipes
- Named pipe ( not our emphasis )
- Like a file (create a named pipe ( mknod ), open,
read/write)
- Can be shared by any process
- Unnamed pipe
- An unnamed pipe does not associate with any
physical file
- It can only be shared by related processes
(descendants of a process that creates the
unnamed pipe)
- Created using system call pipe()
An example for the use of a pipe
- example3.c
- Once the processes can communicate
with each other, their execution order can
be controlled
Implementing pipe in shell
- Example
/usr/bin/ps –ef | /usr/bin/more
- How does the shell realize this command?
- Create a process to run ps -ef
- Create a process to run more
- Create a pipe from ps -ef to more
- The standard output of the process to run ps -ef is redirected to a pipe streaming to the process to run more
- The standard input of the process to run more is redirected to be the pipe from the process running ps –ef
- See example4.c