使用stdin和stdout管道到同一C程序

Question

Let's say I have an executable called myProgram that reads from an input file and writes to an output file. A command line for this program looks like this:

./myProgram -o outputfile inputfile

The argument to the -o option specifies an output file name; if no such file exists then the program will create it.

What I was wondering is whether I can execute myProgram multiple times, piping the output of the one instance to the input of the next. For example,

./myProgram inputfile | ./myProgram -o outputfile

Is it possible to achieve this and if so, what would I have to implement? exec calls and forking? just simple read and write calls?

Answer 1

Pipes work by chaining stdin and stdout of multiple programs together.

You need to modify your program to have the ability to read from stdin and write to stdout instead of to specific files. Then you can use pipes.

Answer 2

The short answer is: yes, you can do this.

However, your program should then read its input from stdin and write to stdout. This means, arguments as input or output file will no longer be necessary.

./myProgram < inputfile > outputfile

or, to illustrate the chaining,

./myProgram < inputfile | ./myProgram > outputfile

A widely spread combination is to read from stdin if no input file is specified and write to stdout if no outputfile or outputfile "-" is passed at the command line. This provides maximum flexibility.

Having said that, if it is sensible to chain multiple instances of the same program depends of course largely on what this program does . For example, for a sorting program this doesn't seem to make much sense of course ;)

Answer 3

与使用命令一起运行程序myProgram的两个实例绝对没有问题

./myProgram inputfile | ./myProgram -o outputfile