TeX needs to know where to find the `texinfo.tex' file that you have told it to input with the `\input texinfo' command at the beginning of the first line. The `texinfo.tex' file tells TeX how to handle @-commands. (`texinfo.tex' is included in the standard GNU distributions.)
Usually, the `texinfo.tex' file is put in the default directory that contains TeX macros (the `/usr/lib/tex/macros' directory) when GNU Emacs or other GNU software is installed. In this case, TeX will find the file and you do not need to do anything special. Alternatively, you can put `texinfo.tex' in the directory in which the Texinfo source file is located, and TeX will find it there.
However, you may want to specify the location of the \input file
yourself. One way to do this is to write the complete path for the file
after the \input command. Another way is to set the
TEXINPUTS environment variable in your `.cshrc' or
`.profile' file. The TEXINPUTS environment variable will tell
TeX where to find the `texinfo.tex' file and any other file that
you might want TeX to use.
Whether you use a `.cshrc' or `.profile' file depends on
whether you use csh, sh, or bash for your shell
command interpreter. When you use csh, it looks to the
`.cshrc' file for initialization information, and when you use
sh or bash, it looks to the `.profile' file.
In a `.cshrc' file, you could use the following csh command
sequence:
setenv TEXINPUTS .:/usr/me/mylib:/usr/lib/tex/macros
In a `.profile' file, you could use the following sh command
sequence:
TEXINPUTS=.:/usr/me/mylib:/usr/lib/tex/macros export TEXINPUTS
This would cause TeX to look for `\input' file first in the current directory, indicated by the `.', then in a hypothetical user's `me/mylib' directory, and finally in the system library.