Clipping a path with TikZ

Question

I understand how to clip with a rectangle, for instance. But how to do it with a different path. I wrote many lines with Bezier curves ( .. controls (,) and (,) ..). So now I have a path with all these Bezier curves. So, how do I clip inside this path? Here is a MWE:

\begin{tikzpicture}[line width=0.8pt]
  \draw (0.1,4.95) .. controls (0.6,4.5) and (1.8,4.15) .. (1.8,3.65);
  \draw (1.8,3.65) .. controls (1.8,2.75) and (1.9,3.15) .. (1.9,2.55);
  \draw (1.9,2.55) .. controls (1.9,2.35) and (2.25,2.15) .. (2.25,1.65);
  \draw (2.25,1.65) .. controls (2.25,1.4) and (1.65,0.8) .. (1.65,0.75);
  \draw (1.65,0.75) .. controls (1.65,0.6) and (1.8,0.54) .. (1.9,0.5);
  \draw (1.9,0.5) .. controls (2,0.44) and (2.5,0.6) .. (2.7,1.05);
  \draw (2.7,1.05) .. controls (3,1.45) and (3,1.5) .. (3,1.8);
  \draw (3,1.8) .. controls (3.05,2.1) and (3.1,2.1) .. (3.4,2);
  \draw (3.4,2) .. controls (3.6,2) and (3.6,1.95) .. (3.8,1.95);
  \draw (3.8,1.95) .. controls (3.85,1.95) and (4.1,1.85) .. (4.2,1.85);
  \draw (4.2,1.85) .. controls (4.4,1.85) and (4.5,1.95) .. (5,2);
  \draw (5,2) .. controls (5.4,1.95) and (5.5,1.95) .. (5.8,1.96);
  \draw (5.8,1.96) .. controls (6.55,1.92) and (6.7,1.94) .. (6.7,2.2);
  \draw (6.7,2.2) .. controls (6.7,2.45) and (6.1,2.5) .. (5.9,2.43);
  \draw (5.9,2.43) .. controls (5.8,2.47) and (5.2,2.55) .. (5.1,2.5);
  \draw (5.1,2.5) .. controls (5.0,2.55) and (5,2.57) .. (4.9,2.6);
  \draw (4.9,2.6) .. controls (4.95,3.0) and (4.95,3.0) .. (4.9,3.6);
  \draw (4.9,3.6) .. controls (4.93,4.0) and (4.9,4.0) .. (4.85,4.5);
  \draw (4.85,4.5) .. controls (4.83,4.8) and (4.8,4.6) .. (4.78,5);
  \draw (4.78,5) .. controls (4.76,5.2) and (4.8,5.0) .. (4.75,5.35);
  \draw (4.75,5.35) .. controls (4.35,5.57) and (4.23,5.0) .. (4.33,4.5);
  \draw (4.33,4.5) .. controls (4.3,4.38) and (4.31,4.4) .. (4.3,4.18);
  \draw (4.3,4.18) -- (4.25,4.16);
  \draw (4.25,4.16) .. controls (4,4.5) and (3.4,4.7) .. (3,4.75);
  \draw (3,4.75) .. controls (2.8,4.8) and (2.65,5.03) .. (2.6,5.05);
  \draw (2.6,5.05) .. controls (2.4,5.15) and (1.75,5.8) .. (1.3,6.25);
\end{tikzpicture}

I can't close the path because I don't want a line between the first and the last point (or an invisible line)

Answer 1

I think you need to close the path:

\documentclass[tikz, border=2mm]{standalone}

\begin{document}
\begin{tikzpicture}
\draw[clip] (0,0)..controls (1,1).. (4,0)..controls (3,-1)..cycle;
\fill[red] (-1,-1) rectangle (2,1);
\fill[green] (2,1) rectangle (4,-1);
\end{tikzpicture}
\end{document}

Update:

The proposed by OP shows several bezier lines that finishes where the new line starts. This way it's easier to build them as one path. This path can be closed to delimit the clip area and be drawn a second time without the closing line.

\documentclass[tikz,border=2mm]{standalone}

\newcommand{\myline}{%
(0.1,4.95) .. controls (0.6,4.5) and (1.8,4.15) .. (1.8,3.65)%;
%  \draw (1.8,3.65) 
  .. controls (1.8,2.75) and (1.9,3.15) .. (1.9,2.55)%;
%  \draw (1.9,2.55) 
  .. controls (1.9,2.35) and (2.25,2.15) .. (2.25,1.65)%;
%  \draw (2.25,1.65) 
  .. controls (2.25,1.4) and (1.65,0.8) .. (1.65,0.75)%;
%  \draw (1.65,0.75) 
  .. controls (1.65,0.6) and (1.8,0.54) .. (1.9,0.5)%;
%  \draw (1.9,0.5) 
  .. controls (2,0.44) and (2.5,0.6) .. (2.7,1.05)%;
%  \draw (2.7,1.05) 
  .. controls (3,1.45) and (3,1.5) .. (3,1.8)%;
%  \draw (3,1.8) 
  .. controls (3.05,2.1) and (3.1,2.1) .. (3.4,2)%;
%  \draw (3.4,2) 
  .. controls (3.6,2) and (3.6,1.95) .. (3.8,1.95)%;
%  \draw (3.8,1.95) 
  .. controls (3.85,1.95) and (4.1,1.85) .. (4.2,1.85)%;
%  \draw (4.2,1.85) 
  .. controls (4.4,1.85) and (4.5,1.95) .. (5,2)%;
%  \draw (5,2) 
  .. controls (5.4,1.95) and (5.5,1.95) .. (5.8,1.96)%;
%  \draw (5.8,1.96) 
  .. controls (6.55,1.92) and (6.7,1.94) .. (6.7,2.2)%;
%  \draw (6.7,2.2) 
  .. controls (6.7,2.45) and (6.1,2.5) .. (5.9,2.43)%;
%  \draw (5.9,2.43) 
  .. controls (5.8,2.47) and (5.2,2.55) .. (5.1,2.5)%;
%  \draw (5.1,2.5) 
  .. controls (5.0,2.55) and (5,2.57) .. (4.9,2.6)%;
%  \draw (4.9,2.6) 
  .. controls (4.95,3.0) and (4.95,3.0) .. (4.9,3.6)%;
%  \draw (4.9,3.6) 
  .. controls (4.93,4.0) and (4.9,4.0) .. (4.85,4.5)%;
%  \draw (4.85,4.5) 
  .. controls (4.83,4.8) and (4.8,4.6) .. (4.78,5)%;
%  \draw (4.78,5) 
  .. controls (4.76,5.2) and (4.8,5.0) .. (4.75,5.35)%;
%  \draw (4.75,5.35) 
  .. controls (4.35,5.57) and (4.23,5.0) .. (4.33,4.5)%;
%  \draw (4.33,4.5) 
  .. controls (4.3,4.38) and (4.31,4.4) .. (4.3,4.18)%;
%  \draw (4.3,4.18) 
  -- (4.25,4.16)%;
%  \draw (4.25,4.16) 
  .. controls (4,4.5) and (3.4,4.7) .. (3,4.75)%;
%  \draw (3,4.75) 
  .. controls (2.8,4.8) and (2.65,5.03) .. (2.6,5.05)%;
%  \draw (2.6,5.05) 
  .. controls (2.4,5.15) and (1.75,5.8) .. (1.3,6.25)}
\begin{document}

\begin{tikzpicture}[line width=0.8pt]
  \path[clip] \myline--cycle;
  \fill[green!90!black] (0,0) rectangle (7,7);
  \draw \myline;
\end{tikzpicture}

\end{document}

Answer 2

You can clip a slightly different path (notice the -| cycle at the end), draw something against that clip and then, outside of the clip, draw the unclosed path.

(As an alternative, a similar thing can be done with a path picture which is basically a one-path clip where the clipping path can be drawn, though. This doesn't help you much since you clipping path and drawn path differ slightly.)

Code

\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}[
  line width=0.8pt,
  hand/.style={insert path={
    (0.1,4.95) .. controls (0.6,4.5) and (1.8,4.15) .. (1.8,3.65)
               .. controls (1.8,2.75) and (1.9,3.15) .. (1.9,2.55)
               .. controls (1.9,2.35) and (2.25,2.15) .. (2.25,1.65)
               .. controls (2.25,1.4) and (1.65,0.8) .. (1.65,0.75)
               .. controls (1.65,0.6) and (1.8,0.54) .. (1.9,0.5)
               .. controls (2,0.44) and (2.5,0.6) .. (2.7,1.05)
               .. controls (3,1.45) and (3,1.5) .. (3,1.8)
               .. controls (3.05,2.1) and (3.1,2.1) .. (3.4,2)
               .. controls (3.6,2) and (3.6,1.95) .. (3.8,1.95)
               .. controls (3.85,1.95) and (4.1,1.85) .. (4.2,1.85)
               .. controls (4.4,1.85) and (4.5,1.95) .. (5,2)
               .. controls (5.4,1.95) and (5.5,1.95) .. (5.8,1.96)
               .. controls (6.55,1.92) and (6.7,1.94) .. (6.7,2.2)
               .. controls (6.7,2.45) and (6.1,2.5) .. (5.9,2.43)
               .. controls (5.8,2.47) and (5.2,2.55) .. (5.1,2.5)
               .. controls (5.0,2.55) and (5,2.57) .. (4.9,2.6)
               .. controls (4.95,3.0) and (4.95,3.0) .. (4.9,3.6)
               .. controls (4.93,4.0) and (4.9,4.0) .. (4.85,4.5)
               .. controls (4.83,4.8) and (4.8,4.6) .. (4.78,5)
               .. controls (4.76,5.2) and (4.8,5.0) .. (4.75,5.35)
               .. controls (4.35,5.57) and (4.23,5.0) .. (4.33,4.5)
               .. controls (4.3,4.38) and (4.31,4.4) .. (4.3,4.18)
               -- (4.25,4.16)
               .. controls (4,4.5) and (3.4,4.7) .. (3,4.75)
               .. controls (2.8,4.8) and (2.65,5.03) .. (2.6,5.05)
               .. controls (2.4,5.15) and (1.75,5.8) .. (1.3,6.25)}}]
\begin{scope}
  \clip[hand] -| cycle;
  \shade[left color=red, right color=green]
              (current bounding box.south west)
    rectangle (current bounding box.north east);
\end{scope}
\draw[hand];

\tikzset{xshift=7cm}
\path[hand] -| cycle [path picture={
  \shade[left color=red, right color=green]
              (path picture bounding box.south west)
    rectangle (path picture bounding box.north east);
}];
\draw[hand];
\end{tikzpicture}
\end{document}

Output