How to find a string occuring between two other strings on other lines

Question

How would I search for a certain string that is preceded by another string, in most cases several lines up, and followed by another string, i.e. contained in a certain environment?

\begin{quote}
%several lines of text
\footnote{%
%probably a few more lines of footnote content
}
%several lines of further text
\end{quote}

Thus I am searching for footnotes (starting with \footnote{) contained in a quote environment (starting with \begin{quote}, ending with end{quote}, in most cases spanning over several lines). Actually, in reality I should search for another environment contained in footnotes which occur inside quote environments, thus adding a second layer of conditions, but probably once I understand the simplified example I can figure out my real world problem. The actual environment I search for occurs about 150 times in a directory containing about 20 .tex files, constituting the sources for a roughly 500 pages book supposed to go to print in a few days, and that particular combination produces an undesired effect, which many times, if not looking carefully, will go unnoticed.

As output of my search I would like to get the file name in which the match occurs (I would probably search through *tex, although, if that should be too complicated, I could also work with a bash for loop), and its line number.

One will also have to keep in mind that

\begin{quote}
%something
\end{quote}
%something
\footnote{%
%something
}
%something
\begin{quote}
%something
\end{quote}

would be something occurring many times, but it would be a false positive.

Answer 1

You can't do this with grep, you'll need something more capable like awk or perl. Here's a very simple example of doing this in perl:

$ cat find-fn-in-quote.pl 
#!/usr/bin/perl

while(<>) {
  # strip comments so that we ignore commented-out quotes & footnotes.
  s/%[^%].*//;

  # detect beginning and end of quotes
  if (m/\Qbegin{quote}\E/) { $qt = 1; $ql = $.};
  if (m/\Qend{quote}\E/)   { $qt = 0 };

  if (eof) {
    # reset line-counter ($.) after every input file
    close(ARGV);

    # reset $qt to zero, in case of unbalanced begin/end{quote}
    $qt = 0;
  };

  # skip to next input line if we're not inside a quote.
  next unless ($qt);

  if (m/\\footnote\{/) {
   print "$ARGV: found footnote beginning on line $. inside quote beginning on line $ql\n";
   # For terse output, comment out or delete the print statement above
   # and un-comment one of these:
   #printf "%s:fn=%i:q=%i\n", $ARGV, $., $ql;
   #printf "%s:%i:%i\n", $ARGV, $., $ql;
  };

};

Note: This script is not capable of properly handling nested begin{quote}s. I doubt that this will be a problem, as it's unlikely to happen outside of contrived examples. It also assumes that a quote will exist entirely within one file - in fact, the script deliberately enforces this to ensure that a bug in one input file (i.e. a missing end{quote}) won't affect subsequent files.

I created 3 text files to test this with. input1.txt contains your first sample input. input2.txt contains your second sample input with the false-positives you don't want to match. input3.txt contains input2.txt followed by input1.txt (i.e. cat input2.txt input1.txt > input3.txt). Running the script on these input files gives the following output:

$ ./find-fn-in-quote.pl *.txt
input1.txt: found footnote beginning on line 3 inside quote beginning on line 1
input3.txt: found footnote beginning on line 14 inside quote beginning on line 12

Answer 2

An awk version of the

awk 'FNR==1{looking=0; print  FILENAME}
  $0~/begin{quote}/{looking=1;next}
  $0~/end{quote}/{looking=0;next}
  looking&&$0~/footnote{/{print FNR, $0}' *.tex

Simply starts "looking" when a quote begins and stops when it ends.

Like @cas example this resets at each opening of a file.

If you are going to be looking inside the footnote for another environment then it gets trickier as you will need to start looking for for balanced } for the \footnote on different lines, which is a different animal.

Answer 3

GNU awk:

awk '
/^\\end{quote}$/ && fire        {report = report OFS str}
/^\\end{quote}$/                {block=cont=fire=0; str=""}
/^\\begin{quote}$/              {block=1}
block && /^\\footnote{%$/       {cont=1; str=FNR; next}
block && cont && /}/            {fire=1;cont=0}
ENDFILE                         {if(report)print FILENAME report; report = ""}
' *.tex

Output format:

filename line_number line_number ...

All line numbers with matches are output in one line for each file. File names without matches are not displayed.