The Linux Programming Interface

Pseudoterminals 1399

One problem with the above scenario is that, by default, the stdio package flushes

standard output only when the stdio buffer is filled. This means that the output from

the longrunner program will appear in bursts separated by long intervals of time. One

way to circumvent this problem is to write a program that does the following:

a) Create a pseudoterminal.

b) Exec the program named in its command-line arguments with the standard

file descriptors connected to the pseudoterminal slave.

c) Read output from the pseudoterminal master and write it immediately to

standard output (STDOUT_FILENO, file descriptor 1), and, at the same time,

read input from the terminal and write it to the pseudoterminal master, so

that it can be read by the execed program.

Such a program, which we’ll call unbuffer, would be used as follows:

$ ./unbuffer longrunner | grep str

Write the unbuffer program. (Much of the code for this program will be similar to

that of Listing 64-3.)

64-8. Write a program that implements a scripting language that can be used to drive vi
in a noninteractive mode. Since vi expects to be run from a terminal, the program
will need to employ a pseudoterminal.