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ncdump(1)                      UNIDATA UTILITIES                     ncdump(1)




NAME

       ncdump - Convert netCDF file to text form (CDL)


SYNOPSIS

       ncdump [-chistxw] [-v var1,...]  [-b lang] [-f lang] [-l len] [-n name]
              [-p f_digits[,d_digits]] [-g grp1,...]  file

       ncdump -k file


DESCRIPTION

       The ncdump utility generates  a  text  representation  of  a  specified
       netCDF file on standard output, optionally excluding some or all of the
       variable data in the output.  The text  representation  is  in  a  form
       called  CDL  (network  Common  Data  form Language) that can be viewed,
       edited, or serve as input to ncgen, a companion program that can gener-
       ate  a  binary netCDF file from a CDL file.  Hence ncgen and ncdump can
       be used as inverses to transform the data representation between binary
       and text representations.  See ncgen documentation for a description of
       CDL and netCDF representations.

       ncdump may also be used to determine what kind of netCDF file  is  used
       (which variant of the netCDF file format) with the -k option.

       If  DAP  support  was  enabled when ncdump was built, the file name may
       specify a DAP URL. This allows ncdump to access data sources  from  DAP
       servers,  including  data in other formats than netCDF.  When used with
       DAP URLs, ncdump shows the translation from the DAP data model  to  the
       netCDF data model.

       ncdump  may  also be used as a simple browser for netCDF data files, to
       display the dimension names and lengths;  variable  names,  types,  and
       shapes;  attribute names and values; and optionally, the values of data
       for all variables or selected variables in a netCDF file.  For netCDF-4
       files,  groups  and user-defined types are also included in ncdump out-
       put.

       ncdump uses `_' to represent data values that are equal to the  `_Fill-
       Value'  attribute  for  a variable, intended to represent data that has
       not yet been written.  If a variable has no `_FillValue' attribute, the
       default fill value for the variable type is used unless the variable is
       of byte type.

       ncdump defines a default display format used for each  type  of  netCDF
       data,  but this can be changed if a `C_format' attribute is defined for
       a netCDF variable.  In this case, ncdump will use  the  `C_format'  at-
       tribute  to format each value.  For example, if floating-point data for
       the netCDF variable `Z' is known to be accurate to only three  signifi-
       cant digits, it would be appropriate to use the variable attribute


              Z:C_format = "%.3g"


OPTIONS

       -c     Show  the  values of coordinate variables (1D variables with the
              same names as dimensions) as well as the declarations of all di-
              mensions,  variables, attribute values, groups, and user-defined
              types.  Data values of non-coordinate variables are not included
              in  the output.  This is usually the most suitable option to use
              for a brief look at the structure and contents of a netCDF file.

       -h     Show  only the header information in the output, that is, output
              only the declarations for the dimensions, variables, attributes,
              groups,  and  user-defined  types of the input file, but no data
              values for any variables.  The output is identical to using  the
              -c option except that the values of coordinate variables are not
              included.  (At most one of -c or -h options may be present.)

       -v var1,...
              The output will include data values for the specified variables,
              in  addition  to  the declarations of all dimensions, variables,
              and attributes.  One or more variables must be specified by name
              in  the  comma-delimited  list  following this option.  The list
              must be a single argument to the command, hence  cannot  contain
              unescaped  blanks  or  other  white space characters.  The named
              variables must be valid netCDF variables in the  input-file.   A
              variable within a group in a netCDF-4 file may be specified with
              an absolute path name, such as `/GroupA/GroupA2/var'.  Use of  a
              relative  path  name  such  as  `var' or `grp/var' specifies all
              matching variable names in the file.  The default, without  this
              option and in the absence of the -c or -h options, is to include
              data values for all variables in the output.

       -b [c|f]
              A brief annotation in the form of a CDL comment (text  beginning
              with the characters ``//'') will be included in the data section
              of the output for each `row' of data, to help identify data val-
              ues  for multidimensional variables.  If lang begins with `C' or
              `c', then C language conventions will be  used  (zero-based  in-
              dices, last dimension varying fastest).  If lang begins with `F'
              or `f', then Fortran language conventions  will  be  used  (one-
              based  indices,  first  dimension  varying  fastest).  In either
              case, the data will be presented in the same order; only the an-
              notations  will  differ.  This option may be useful for browsing
              through large volumes of multidimensional data.

       -f [c|f]
              Full annotations in the form of trailing CDL comments (text  be-
              ginning with the characters ``//'') for every data value (except
              individual characters in character arrays) will be  included  in
              the  data  section.  If lang begins with `C' or `c', then C lan-
              guage conventions will be used.  If lang begins with `F' or `f',
              then Fortran language conventions will be used.  In either case,
              the data will be presented in the same order; only  the  annota-
              tions  will  differ.   This option may be useful for piping data
              into other filters, since each data value appears on a  separate
              line, fully identified. (At most one of '-b' or '-f' options may
              be present.)

       -l length
              Changes the default maximum line length (80) used in  formatting
              lists of non-character data values.

       -n name
              CDL  requires  a  name for a netCDF file, for use by ncgen -b in
              generating a default netCDF file name.  By default, ncdump  con-
              structs  this  name  from the last component of the file name of
              the input netCDF file by stripping off  any  extension  it  has.
              Use  the  -n  option  to specify a different name.  Although the
              output file name used by ncgen -b can be specified,  it  may  be
              wise  to  have  ncdump change the default name to avoid inadver-
              tently overwriting a valuable netCDF  file  when  using  ncdump,
              editing the resulting CDL file, and using ncgen -b to generate a
              new netCDF file from the edited CDL file.

       -p float_digits[,double_digits]
              Specifies default precision (number of  significant  digits)  to
              use in displaying floating-point or double precision data values
              for attributes and variables.  If specified,  this  value  over-
              rides  the  value of the C_format attribute, if any, for a vari-
              able.  Floating-point data will be displayed  with  float_digits
              significant digits.  If double_digits is also specified, double-
              precision values will be displayed with  that  many  significant
              digits.  In the absence of any -p specifications, floating-point
              and double-precision data are displayed with 7 and  15  signifi-
              cant digits respectively.  CDL files can be made smaller if less
              precision is required.  If both floating-point and double preci-
              sions  are  specified, the two values must appear separated by a
              comma (no blanks) as a single argument to the command.  (To rep-
              resent  every last bit of precision in a CDL file for all possi-
              ble floating-point values would require -p 9,17.)

       -k     Show kind of netCDF file the pathname references, one of  `clas-
              sic',  `64-bit  offset',`netCDF-4', or `netCDF-4 classic model'.
              Before version 3.6, there was only one kind of netCDF file, des-
              ignated  as  `classic'  (also  know as format variant 1).  Large
              file support introduced another variant of the format, designat-
              ed  as  `64-bit  offset' (known as format variant 2).  NetCDF-4,
              uses a third variant of the format, `netCDF-4'  (format  variant
              3).  Another format variant, designated `netCDF-4 classic model'
              (format variant 4), is restricted to features supported  by  the
              netCDF-3  data  model  but represented using the HDF5 format, so
              that an unmodified netCDF-3 program can read or write  the  file
              just  by relinking with the netCDF-4 library.  The string output
              by using the `-k' option may be provided as  the  value  of  the
              `-k'  option  to ncgen(1) to specify exactly what kind of netCDF
              file to generate, when you want to override the default inferred
              from the CDL.

       -s     Output  special  virtual attributes that provide performance-re-
              lated information about the file format and variable  properties
              for netCDF-4 data.  These special virtual attributes are not ac-
              tually part of the data, they are merely  a  convenient  way  to
              display miscellaneous properties of the data in CDL (and eventu-
              ally NcML).  They include `_ChunkSizes', `_DeflateLevel',  `_En-
              dianness',  `_Fletcher32', `_Format', `_NoFill', `_Shuffle', and
              `_Storage'.  `_ChunkSizes' is a list of chunk sizes for each di-
              mension  of the variable.  `_DeflateLevel' is an integer between
              0 and 9 inclusive if compression  has  been  specified  for  the
              variable.   `_Endianness' is either `little' or `big', depending
              on how the variable was stored when  first  written.   `_Fletch-
              er32'  is  `true' if the checksum property was set for the vari-
              able.  `_Format' is a global  attribute  specifying  the  netCDF
              format  variant,  one of `classic', `64-bit offset', `netCDF-4',
              or `netCDF-4 classic model'.  `_NoFill' is `true' if the persis-
              tent  NoFill  property  was set for the variable when it was de-
              fined.  `_Shuffle' is `true' if use of the  shuffle  filter  was
              specified for the variable.  `_Storage' is `contiguous' or `com-
              pact' or `chunked', depending on  how  the  variable's  data  is
              stored.

       -t     Controls display of time data, if stored in a variable that uses
              a udunits compliant time  representation  such  as  `days  since
              1970-01-01'  or  `seconds since 2009-03-15 12:01:17', a variable
              identified in a "bounds" attribute of such a time variable, or a
              numeric  attribute of a time variable.  If this option is speci-
              fied, time data values are displayed as human-readable date-time
              strings  rather than numerical values, interpreted in terms of a
              `calendar' variable attribute, if specified.   For  numeric  at-
              tributes  of  time  variables,  the human-readable time value is
              displayed after the actual value, in an associated CDL  comment.
              Calendar  attribute  values interpreted with this option include
              the CF Conventions values `gregorian'  or  `standard',  `prolep-
              tic_gregorian',  `noleap' or `365_day', `all_leap' or `366_day',
              `360_day', and `julian'.

       -i     Same as the '-t' option, except output time  data  as  date-time
              strings  with  ISO-8601  standard  'T'  separator,  instead of a
              blank.

       -g grp1,...
              For netCDF-4 files, the output will include data values only for
              the  specified  groups.  One or more groups must be specified by
              name in the comma-delimited list following this option. The list
              must  be a single argument to the command. The named groups must
              be valid netCDF groups in the input-file.  A group in a netCDF-4
              file  may  be  specified with an absolute or relative path name.
              Use of a relative path name specifies all matching  group  names
              in  the  file.   The default, without this option and in the ab-
              sence of the -c or -h options, is to include data values for all
              groups in the output.

       -w     For file names that request remote access using DAP URLs, access
              data with client-side caching of entire variables.

       -x     Output XML (NcML) instead of CDL.  The NcML does not include da-
              ta  values.   The  NcML  output  option currently only works for
              netCDF classic model data.


EXAMPLES

       Look at the structure of the data in the netCDF file `foo.nc':

              ncdump -c foo.nc

       Produce an annotated CDL version of  the  structure  and  data  in  the
       netCDF file `foo.nc', using C-style indexing for the annotations:

              ncdump -b c foo.nc > foo.cdl

       Output  data for only the variables `uwind' and `vwind' from the netCDF
       file `foo.nc', and show the floating-point data with only three signif-
       icant digits of precision:

              ncdump -v uwind,vwind -p 3 foo.nc

       Produce a fully-annotated (one data value per line) listing of the data
       for the variable `omega', using Fortran conventions  for  indices,  and
       changing the netCDF dataset name in the resulting CDL file to `omega':

              ncdump -v omega -f fortran -n omega foo.nc > Z.cdl


SEE ALSO

       ncgen(1), netcdf(3)


BUGS

       Character  arrays  that contain a null-byte are treated like C strings,
       so no characters after the null byte appear in the output.

       Multidimensional character string arrays are not  handled  well,  since
       the CDL syntax for breaking a long character string into several short-
       er lines is weak.

       There should be a way to specify that the data should be  displayed  in
       `record'  order, that is with the all the values for `record' variables
       together that have the same value of the record dimension.



Release 4.2                       2012-03-08                         ncdump(1)

netcdf 4.7.4 - Generated Thu Apr 16 19:25:45 CDT 2020
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