Linux Kernel write() - Shell-Bash

When working with Linux systems, chances are we'll encounter the write() system call. In this article, we'll explore the basics of write() and its role in the Linux kernel. Additionally, we'll look at some practical examples of using write() in Shell-Bash for writing data to files and streams.

Overview of write()

write() is a system call used to write data to a file descriptor. It is defined in the unistd.h header file and has the following prototype:

ssize_t write(int fd, const void *buf, size_t count);

The fd parameter is the file descriptor that the data will be written to. buf points to the buffer containing the data that will be written, and count is the number of bytes to be written.

When write() is called, it returns the number of bytes that it actually wrote to the file. If write() fails, it will return -1 and set errno to indicate the error.

Using write() in Shell-Bash

In Shell-Bash, we can use write() to write data to files and streams. Here is a basic example:

#!/bin/bash
message="Hello World!"
echo "$message" | write 0

This script writes the message "Hello World!" to the console using the write() system call. The 0 parameter refers to stdout, which is where the output will be written.

We can also use write() to write to files:

#!/bin/bash
message="Hello World!"
echo "$message" | write 1 > file.txt

This script writes the message "Hello World!" to a file named file.txt. The 1 parameter refers to the file descriptor for stdout, which is where the output will be written. We redirect the output of the script to file.txt.

Conclusion

In conclusion, write() is a fundamental system call in the Linux kernel used for writing data to a file descriptor. In Shell-Bash, write() can be used to write data to files and streams. By familiarizing ourselves with write() and its uses, we can become more effective programmers on Linux systems.