function replace_string, label, keyword, old_string, new_string

;+
;$Log:
;
; NAME:
;   replace_string
;
; PURPOSE:
;   Replace specific strings of label contents
;
; CATEGORY:
;   AMIE Calibration
;
; CALLING SEQUENCE:
;   new_label = replace_string(label, keyword, old_string, new_string)
;
; INPUTS:
;   label: the label from which the contents will be modified
;   keyword: the label keyword from which the string to be modified belongs
;   old_string: the string that must be modified
;   new_string: new value for the string
;
; OPTIONAL INPUT PARAMETERS:
;   None.
;
; OUTPUTS:
;    label with modified contents
;
; COMMON BLOCKS:
;   None.
;
; SIDE EFFECTS:
;   Hopefully none.
;
; RESTRICTIONS:
;   New string must have the same size as the old one
;
; MODIFICATION HISTORY:
;   2004 Feb 18, MA: First version
;
; (c) 2004, Miguel Almeida, ESA/RSSD
;-

keyword_content = pdspar(label, keyword)
string_pos = strpos(keyword_content, old_string)

if string_pos gt 0 then begin

    strput, keyword_content, new_string, string_pos
    label = pdsupdatekeyword(label, keyword, keyword_content(0))

endif

return, label

end