\input only part of a file

Question

I would like to include part of the contents of a .tex file into a different .tex file. I don't have the option of modifying the file to include. The file to include may change so simply copying and pasting the part I need is not ideal.

Essentially, I'm wondering if there is something that would work like

\input[start-end]{file.tex}

where start and end are the first and last lines to include from the file?

Answer 1

Here is an approach in pure TeX (well, e-TeX). The main idea is: to select a range of lines in a file, sed is overkill, TeX is more than enough. As a bonus, no temporary file is needed.

\documentclass[a4paper]{article}
\usepackage[ascii]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\makeatletter
\newread\pin@file
\newcounter{pinlineno}
\newcommand\pin@accu{}
\newcommand\pin@ext{pintmp}
% inputs #3, selecting only lines #1 to #2 (inclusive)
\newcommand*\partialinput [3] {%
  \IfFileExists{#3}{%
    \openin\pin@file #3
    % skip lines 1 to #1 (exclusive)
    \setcounter{pinlineno}{1}
    \@whilenum\value{pinlineno}<#1 \do{%
      \read\pin@file to\pin@line
      \stepcounter{pinlineno}%
    }
    % prepare reading lines #1 to #2 inclusive
    \addtocounter{pinlineno}{-1}
    \let\pin@accu\empty
    \begingroup
    \endlinechar\newlinechar
    \@whilenum\value{pinlineno}<#2 \do{%
      % use safe catcodes provided by e-TeX's \readline
      \readline\pin@file to\pin@line
      \edef\pin@accu{\pin@accu\pin@line}%
      \stepcounter{pinlineno}%
    }
    \closein\pin@file
    \expandafter\endgroup
    \scantokens\expandafter{\pin@accu}%
  }{%
    \errmessage{File `#3' doesn't exist!}%
  }%
}
\makeatother

% for testing purpose
\begin{filecontents}{pitest}
5 You shouldn't see this.\par
6 Let the fun begin!
7 \iffalse
8 bla
9 \fi

11 New paragraph.
12 \verb*+\foo (two  spaces)~_$^+ bla
13 You shouldn't see this.\par
\end{filecontents}

\begin{document}

\partialinput{6}{12}{pitest} random text

\end{document}

I think/hope this approach is robust, mostly thanks to e-TeX's \readline. See the included test file for potential edge cases that do work.

Answer 2

Manuel has posted an answer that uses line numbers; there's a recent package on CTAN that lets you do it with tags in the input file: catchfilebetweentags.

An example is

\usepackage{catchfilebetweentags}
...
\ExecuteMetaData[file.tex]{tag}

where the contents of the external file is surrounded by the "tags":

%<*tag>
...
%</tag>

Answer 3

As is stated in the comments, sed -ne 42,99p will copy lines 42–99 (inclusive) from its input to its output. That is assuming you're on some sort of unix (though I suppose you can have sed on windows too). You can do this in a script or a makefile, putting the result in a temporary file that you include.

Alternatively, assuming you are on unix, you can resort to some mild unix wizardry: Say the TeX file you want to include part of, is named foo.tex. Then you can do

mkfifo foosnips.tex
while sed -ne 42,99p foo.tex > foosnips.tex || [ $? == 141 ]; do sleep 1; done &

(modify for your shell if it's not (ba)sh) and then input foosnips in your master TeX file. Each time you TeX it, the sed command will extract the requested lines. The background job should keep on running until you reboot the computer, but thanks to the way fifos work, it will not actually do anything until the fifo is opened for reading. Kill it by hand when it is no longer needed, or if you need to adjust the parameters.

Doing it that way is perhaps not worth it, unless foo.tex changes very often, or the extract is very large and you don't want to keep it as a separate file.

(The test for exit status 141 (128+13, where 13 is the signal number of the PIPE signal) is there to make sure the loop is not terminated if you read only part of the output from the fifo, as when TeX is quit due to some error. And the sleep is needed to make sure the process at the receiving end of the fifo has a chance to close the file before a new sed process starts.)

Answer 4

Here's something that's totally untested!

\newread\pin
\newcount\pcount
\def\partialinput[#1-#2]#3{%
    \openin\pin #3
    \global\pcount0
    \loop\ifnum\pcount<#1\relax
        \read\pin to\l
        \global\advance\pcount1
    \repeat
    \loop\ifnum\pcount<#2\relax
        \read\pin to\l\l
        \global\advance\pcount1
    \repeat
    \read\pin to\l\l
    \closein\pin
}

Modulo errors, that defines a new macro \partialinput that should work as you describe.

Actually, that numbers lines starting at 0. replace the \global\pcount0 with \global\pcount1 to start at 1 instead.