A way to catch MCNP histograms...

... with a shellscript?

You could add the following function to your .bashrc.

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function mcnpplot() { sed -n "/$2/,/total/p" $1 | sed '1,3d' | sed '$d' | xgraph -lnx -bg white -fmtx %.1e -x Energy\ [MeV] -y Normalized\ Fluence\ [A.U.] -t "$1" ; } 

#usage: > mcnpplot myMCNP_outputFile "surface  51"
# The 2nd argument corresponds to the string from which you want to get the data. 
# Do not forget the double quotes and the double space!
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It requires xgraph to be installed.

... with Root?

Here's a basic ROOT function to extract histogram from a MCNP file:

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#include <TH1D.h>
#include <vector>

/////

template <typename myType>
myType* myRootFunctions_getArrayFromVector (vector<myType>* myVector)
{
   Int_t nElt = myVector->size() ; 
   myType *myArray = new myType [nElt] ;
   for (Int_t i=0 ; i<nElt ; i++) { myArray[i] = myVector->at(i) ; } 
   return (myArray) ; 
}

/////

TH1D* myRootFunctions_getMCNPhisto (TString finName, TString histoName, TString str_start, Int_t nJumps=2, TString str_stop="total")  // read MCNP File
// Call: TH1D* histo = myRootFunctions_getMCNPhisto ("myMCNPFile.out", "myHisto", "   surface  51")
{      
   vector<Double_t> *vect_energy = new vector<Double_t>, *vect_tally = new vector<Double_t>, *vect_dtally_tally = new vector<Double_t> ; 
   TString str_energy, str_tally, str_dtally_tally ; 
   Char_t energy[20], tally[20], dtally_tally[20], dummy[300]="" ; 

   FILE* fin = fopen(finName.Data(),"r") ; 
   if ( fin == NULL ) { fprintf (stderr, "\n\n!!! Error in 'myRootFunctions_getMCNPhisto': '%s' cannot be opened or read. It may not exist!\n\n",finName.Data()) ; getchar() ; exit(1) ; } 
      
      do { fgets (dummy,300,fin) ; } while ( TString(dummy).Contains(str_start)==kFALSE && !feof(fin) ) ; 
      if ( feof(fin) ) { fprintf (stderr,"\n\n!!! Error in 'myRootFunctions_getMCNPhisto': string '%s' cannot be found!\n\n",str_start.Data()) ; getchar() ; exit(1) ; }

      for (Int_t i=0; i<nJumps; i++) { fgets (dummy,300,fin) ; }  //fprintf (stdout,"\n%s\n",dummy) ; getchar() ; 
      do 
      { 
         fscanf (fin,"%s %s %s",energy,tally,dtally_tally) ; 
         str_energy = energy ; str_tally = tally ; str_dtally_tally = dtally_tally ; 
         //fprintf (stdout,"\n%s %s %s",str_energy.Data(),str_tally.Data(),str_dtally_tally.Data()) ;
         if ( str_energy != str_stop ) { vect_energy->push_back(str_energy.Atof()) ; vect_tally->push_back(str_tally.Atof()) ; vect_dtally_tally->push_back(str_dtally_tally.Atof()) ; }
      } 
      while ( str_energy != str_stop ) ; //fprintf (stdout,"\n") ;

   fclose (fin) ; 

   Int_t nPoints = Int_t (vect_energy->size()), nBins = nPoints-1 ; 

   TH1D* histo = new TH1D (histoName,histoName,nBins,myRootFunctions_getArrayFromVector<Double_t>(vect_energy)) ;
   for (Int_t binNumber=1; binNumber<=nBins; binNumber++) 
   {
      histo->SetBinContent(binNumber,vect_tally->at(binNumber)) ; 
      histo->SetBinError  (binNumber,vect_tally->at(binNumber)*vect_dtally_tally->at(binNumber)) ;
   }
   delete vect_energy       ; vect_energy       = NULL ; 
   delete vect_tally        ; vect_tally        = NULL ; 
   delete vect_dtally_tally ; vect_dtally_tally = NULL ; 

   return (histo) ; 
}
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To use it, copy it in a separate file, let's say getmcnp.c and execute the following macro:

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{
gROOT->Reset() ;
gROOT->ProcessLine(".L getmcnp.c+") ;
TH1D* histo = myRootFunctions_getMCNPhisto ("myMCNPfile.out", "myHistoName", "cell  4", 2, "total") ;
histo->SetXTitle("Kinetic energy  [MeV]") ; histo->GetXaxis()->CenterTitle() ; 
histo->SetYTitle("Normalized Fluence"   ) ; histo->GetYaxis()->CenterTitle() ; 
histo->SetLineColor(kRed) ; 
histo->SetMinimum(0.) ; 
histo->Draw("hist e") ;
}
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If you use NEdit, please see here.