Question

i am trying to implement the more command. I want to learn that how can I understand if there is a pipe. For example, if I type from the shell

cat file1 file2 | more

how can I handle that inside the implementation of more?

And is the implementation of more available as open source?

Actually i could not succeed from reading stdin.I’ve managed doing more file.txt but not cat file | more..

i think i should first read from user and put a buffer than print the buffer. my code contains:

if(argc == 1)
{
  fgets(line, 255, 0);
   printf("%s", line);
} 

but it gives error.

Answer 1

The more syntax is

more [options] [file_name]

If you don’t provide a file name, the more command gets input from stdin; you can provide this input (via stdin) using a pipe, for example:

cat file.txt | more

This sends the output of the cat command to more. This is the same as doing:

more file.txt

You don’t need to specifically know if there is a pipe or not; you just need to check if a filename was passed as argument to more. If so, the input is considered to be the contents of the file. If not, the input is considered to originate from stdin.

As for the source code, some google searching will take you a long way. Here is some old source code from FreeBSD:

http://svnweb.freebsd.org/base/stable/2.0.5/usr.bin/more/

Or more recente source from the Ubuntu repositories:

http://bazaar.launchpad.net/~vcs-imports/util-linux-ng/trunk/files/head:/text-utils/