This is proc/necho.c (Listing 6-2, page 123), an example from the book, The Linux Programming Interface.
The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.
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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.
/* necho.c A simple version of echo(1): echo our command-line arguments. */ #include "tlpi_hdr.h"
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