\documentclass[a4paper]{article}
\usepackage{pgfplotstable}

\newcount\filecount
\newwrite\cisout
\begin{document}


{
\endlinechar=\newlinechar%
\filecount=1 %
\def\aaa{file number \the\filecount}%
\loop%
\immediate\openout\cisout=data\the\filecount.txt %
\immediate\write\cisout{%
1, 2,   \aaa
}%
\immediate\closeout\cisout %
\advance\filecount by 1 %
\ifnum\filecount<5 %
\ifnum\the\filecount=1 \pgfplotstableread[]{data1.txt}{\main} \else\fi
\repeat %
}%

\pgfplotstabletypeset[col sep=comma]{\main}

\documentclass{article}
\usepackage{scrlfile}
\usepackage{filehook}

\begin{document}

\end{document}

Package filehook Warning: Macro \InputIfFileExists got redefined after 'filehoo
k' was loaded.
Certain file hooks might now be dysfunctional! on input line 5.

\documentclass{article}
\usepackage{filehook}
\usepackage{scrlfile}


\begin{document}

\end{document}

LaTeX Warning: Command \InputIfFileExists  has changed.
               Check if current package is valid.


LaTeX Warning: Command \InputIfFileExists   has changed.
               Check if current package is valid.

) (/usr/local/texlive/2019/texmf-dist/tex/latex/filehook/filehook-scrlfile.sty

! Package filehook Error: Detected 'scrlfile' package with unknown definition o
f \InputIfFileExists.
Use the 'force' option of 'filehook' to overwrite it..