;+
; NAME:
;  nthline
;
; PURPOSE: (one line)
;  Return the nth line in a file
;
; DESCRIPTION:
;  Return the nth line in a file
;
; CATEGORY:
;  File IO
;  
; CALLING SEQUENCE:
;  line = nthline(filename, linenum)
;
; INPUTS:
;  filename - file from which to get lines
;  linenum - the line number to return (long or array of long)
;
; OPTIONAL INPUT PARAMETERS:
;  None
;  
; KEYWORD INPUT PARAMETERS:
;  /VERBOSE -- If set, print diagnostics to screen.
;
; KEYWORD OUTPUT PARAMETERS:
;  NSTARS -- Returns the number of successfully-retrieved lines.
;
; OUTPUTS:
;  If input is a scalar, then output is a single string.
;  If input is a vector, then output is an array of strings.
;  If a line is not found (linenum out of range), returned value is ''.
;  
; COMMON BLOCKS:
;  None
;
; SIDE EFFECTS:
;  None
;
; PROCEDURES:
;  repeated calls to readf
;
; RESTRICTIONS:
;
; EXAMPLE:
;  print, nthline(102,[430L, 1000L])
; 
; MODIFICATION HISTORY:
;  Written   2006 Apr 23 Leslie Young SwRI
;-
function nthline, filename, linenum

    openr, lun, filename, /get_lun
    
    nline = n_elements(linenum)
    lines = strarr(nline)
    s = sort(linenum)
    
    n = -1L                     ; number of lines read in the file
    i = 0L
    cont = 1
    while i lt nline and cont do begin
        nextnum = linenum[s[i]]
;        print, i, nextnum
        tmp = ' '
        while not eof(lun) and n lt nextnum do begin
            n = n + 1
            readf,lun,tmp
        endwhile

        if n eq nextnum then begin
             lines[i] = tmp
            i = i + 1
        endif else begin
            cont = 0
        endelse
    end
    close, lun & free_lun,lun

    return, lines
       
end