1NCDUMP(1)                      UNIDATA UTILITIES                     NCDUMP(1)
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NAME

6       ncdump - Convert netCDF file to text form (CDL)
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SYNOPSIS

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

15       The ncdump utility generates  a  text  representation  of  a  specified
16       netCDF file on standard output, optionally excluding some or all of the
17       variable data in the output.  The text  representation  is  in  a  form
18       called  CDL  (network  Common  Data  form Language) that can be viewed,
19       edited, or serve as input to ncgen, a companion program that can gener‐
20       ate  a  binary netCDF file from a CDL file.  Hence ncgen and ncdump can
21       be used as inverses to transform the data representation between binary
22       and text representations.  See ncgen documentation for a description of
23       CDL and netCDF representations.
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25       ncdump may also be used to determine what kind of netCDF file  is  used
26       (which variant of the netCDF file format) with the -k option.
27
28       If  DAP  support  was  enabled when ncdump was built, the file name may
29       specify a DAP URL. This allows ncdump to access data sources  from  DAP
30       servers,  including  data in other formats than netCDF.  When used with
31       DAP URLs, ncdump shows the translation from the DAP data model  to  the
32       netCDF data model.
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34       ncdump  may  also be used as a simple browser for netCDF data files, to
35       display the dimension names and lengths;  variable  names,  types,  and
36       shapes;  attribute names and values; and optionally, the values of data
37       for all variables or selected variables in a netCDF file.  For netCDF-4
38       files,  groups  and user-defined types are also included in ncdump out‐
39       put.
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41       ncdump uses `_' to represent data values that are equal to the  `_Fill‐
42       Value'  attribute  for  a variable, intended to represent data that has
43       not yet been written.  If a variable has no `_FillValue' attribute, the
44       default fill value for the variable type is used unless the variable is
45       of byte type.
46
47       ncdump defines a default display format used for each  type  of  netCDF
48       data,  but this can be changed if a `C_format' attribute is defined for
49       a netCDF variable.  In this case, ncdump will use the `C_format' attri‐
50       bute to format each value.  For example, if floating-point data for the
51       netCDF variable `Z' is known to be accurate to only  three  significant
52       digits, it would be appropriate to use the variable attribute
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55              Z:C_format = "%.3g"
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OPTIONS

58       -c     Show  the  values of coordinate variables (1D variables with the
59              same names as dimensions) as well as the declarations of all di‐
60              mensions,  variables, attribute values, groups, and user-defined
61              types.  Data values of non-coordinate variables are not included
62              in  the output.  This is usually the most suitable option to use
63              for a brief look at the structure and contents of a netCDF file.
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65       -h     Show only the header information in the output, that is,  output
66              only the declarations for the dimensions, variables, attributes,
67              groups, and user-defined types of the input file,  but  no  data
68              values  for any variables.  The output is identical to using the
69              -c option except that the values of coordinate variables are not
70              included.  (At most one of -c or -h options may be present.)
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72       -v var1,...
73              The output will include data values for the specified variables,
74              in addition to the declarations of  all  dimensions,  variables,
75              and attributes.  One or more variables must be specified by name
76              in the comma-delimited list following  this  option.   The  list
77              must  be  a single argument to the command, hence cannot contain
78              unescaped blanks or other white  space  characters.   The  named
79              variables  must  be valid netCDF variables in the input-file.  A
80              variable within a group in a netCDF-4 file may be specified with
81              an  absolute path name, such as `/GroupA/GroupA2/var'.  Use of a
82              relative path name such as  `var'  or  `grp/var'  specifies  all
83              matching  variable names in the file.  The default, without this
84              option and in the absence of the -c or -h options, is to include
85              data values for all variables in the output.
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87       -b [c|f]
88              A  brief annotation in the form of a CDL comment (text beginning
89              with the characters ``//'') will be included in the data section
90              of the output for each `row' of data, to help identify data val‐
91              ues for multidimensional variables.  If lang begins with `C'  or
92              `c',  then  C  language conventions will be used (zero-based in‐
93              dices, last dimension varying fastest).  If lang begins with `F'
94              or  `f',  then  Fortran  language conventions will be used (one-
95              based indices, first  dimension  varying  fastest).   In  either
96              case, the data will be presented in the same order; only the an‐
97              notations will differ.  This option may be useful  for  browsing
98              through large volumes of multidimensional data.
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100       -f [c|f]
101              Full  annotations in the form of trailing CDL comments (text be‐
102              ginning with the characters ``//'') for every data value (except
103              individual  characters  in character arrays) will be included in
104              the data section.  If lang begins with `C' or `c', then  C  lan‐
105              guage conventions will be used.  If lang begins with `F' or `f',
106              then Fortran language conventions will be used.  In either case,
107              the  data  will be presented in the same order; only the annota‐
108              tions will differ.  This option may be useful  for  piping  data
109              into  other filters, since each data value appears on a separate
110              line, fully identified. (At most one of '-b' or '-f' options may
111              be present.)
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113       -l length
114              Changes  the default maximum line length (80) used in formatting
115              lists of non-character data values.
116
117       -n name
118              CDL requires a name for a netCDF file, for use by  ncgen  -b  in
119              generating  a default netCDF file name.  By default, ncdump con‐
120              structs this name from the last component of the  file  name  of
121              the  input  netCDF  file  by stripping off any extension it has.
122              Use the -n option to specify a  different  name.   Although  the
123              output  file  name  used by ncgen -b can be specified, it may be
124              wise to have ncdump change the default name  to  avoid  inadver‐
125              tently  overwriting  a  valuable  netCDF file when using ncdump,
126              editing the resulting CDL file, and using ncgen -b to generate a
127              new netCDF file from the edited CDL file.
128
129       -p float_digits[,double_digits]
130              Specifies  default  precision  (number of significant digits) to
131              use in displaying floating-point or double precision data values
132              for  attributes  and  variables.  If specified, this value over‐
133              rides the value of the C_format attribute, if any, for  a  vari‐
134              able.   Floating-point  data will be displayed with float_digits
135              significant digits.  If double_digits is also specified, double-
136              precision  values  will  be displayed with that many significant
137              digits.  In the absence of any -p specifications, floating-point
138              and  double-precision  data are displayed with 7 and 15 signifi‐
139              cant digits respectively.  CDL files can be made smaller if less
140              precision is required.  If both floating-point and double preci‐
141              sions are specified, the two values must appear separated  by  a
142              comma (no blanks) as a single argument to the command.  (To rep‐
143              resent every last bit of precision in a CDL file for all  possi‐
144              ble floating-point values would require -p 9,17.)
145
146       -k     Show  kind of netCDF file the pathname references, one of `clas‐
147              sic', `64-bit offset',`netCDF-4', or `netCDF-4  classic  model'.
148              Before version 3.6, there was only one kind of netCDF file, des‐
149              ignated as `classic' (also know as  format  variant  1).   Large
150              file support introduced another variant of the format, designat‐
151              ed as `64-bit offset' (known as format  variant  2).   NetCDF-4,
152              uses  a  third variant of the format, `netCDF-4' (format variant
153              3).  Another format variant, designated `netCDF-4 classic model'
154              (format  variant  4), is restricted to features supported by the
155              netCDF-3 data model but represented using the  HDF5  format,  so
156              that  an  unmodified netCDF-3 program can read or write the file
157              just by relinking with the netCDF-4 library.  The string  output
158              by  using  the  `-k'  option may be provided as the value of the
159              `-k' option to ncgen(1) to specify exactly what kind  of  netCDF
160              file to generate, when you want to override the default inferred
161              from the CDL.
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163       -s     Output special virtual attributes that  provide  performance-re‐
164              lated  information about the file format and variable properties
165              for netCDF-4 data.  These special virtual attributes are not ac‐
166              tually  part  of  the  data, they are merely a convenient way to
167              display miscellaneous properties of the data in CDL (and eventu‐
168              ally  NcML).  They include `_ChunkSizes', `_DeflateLevel', `_En‐
169              dianness', `_Fletcher32', `_Format', `_NoFill', `_Shuffle',  and
170              `_Storage'.  `_ChunkSizes' is a list of chunk sizes for each di‐
171              mension of the variable.  `_DeflateLevel' is an integer  between
172              0  and  9  inclusive  if  compression has been specified for the
173              variable.  `_Endianness' is either `little' or `big',  depending
174              on  how  the  variable was stored when first written.  `_Fletch‐
175              er32' is `true' if the checksum property was set for  the  vari‐
176              able.   `_Format'  is  a  global attribute specifying the netCDF
177              format variant, one of `classic', `64-bit  offset',  `netCDF-4',
178              or `netCDF-4 classic model'.  `_NoFill' is `true' if the persis‐
179              tent NoFill property was set for the variable when  it  was  de‐
180              fined.   `_Shuffle'  is  `true' if use of the shuffle filter was
181              specified for the variable.  `_Storage' is `contiguous' or `com‐
182              pact'  or  `chunked',  depending  on  how the variable's data is
183              stored.
184
185       -t     Controls display of time data, if stored in a variable that uses
186              a  udunits  compliant  time  representation  such as `days since
187              1970-01-01' or `seconds since 2009-03-15 12:01:17',  a  variable
188              identified in a "bounds" attribute of such a time variable, or a
189              numeric attribute of a time variable.  If this option is  speci‐
190              fied, time data values are displayed as human-readable date-time
191              strings rather than numerical values, interpreted in terms of  a
192              `calendar'  variable  attribute,  if specified.  For numeric at‐
193              tributes of time variables, the  human-readable  time  value  is
194              displayed  after the actual value, in an associated CDL comment.
195              Calendar attribute values interpreted with this  option  include
196              the  CF  Conventions  values `gregorian' or `standard', `prolep‐
197              tic_gregorian', `noleap' or `365_day', `all_leap' or  `366_day',
198              `360_day', and `julian'.
199
200       -i     Same  as  the  '-t' option, except output time data as date-time
201              strings with ISO-8601  standard  'T'  separator,  instead  of  a
202              blank.
203
204       -g grp1,...
205              For netCDF-4 files, the output will include data values only for
206              the specified groups.  One or more groups must be  specified  by
207              name in the comma-delimited list following this option. The list
208              must be a single argument to the command. The named groups  must
209              be valid netCDF groups in the input-file.  A group in a netCDF-4
210              file may be specified with an absolute or  relative  path  name.
211              Use  of  a relative path name specifies all matching group names
212              in the file.  The default, without this option and  in  the  ab‐
213              sence of the -c or -h options, is to include data values for all
214              groups in the output.
215
216       -w     For file names that request remote access using DAP URLs, access
217              data with client-side caching of entire variables.
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219       -x     Output XML (NcML) instead of CDL.  The NcML does not include da‐
220              ta values.  The NcML output  option  currently  only  works  for
221              netCDF classic model data.
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EXAMPLES

224       Look at the structure of the data in the netCDF file `foo.nc':
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226              ncdump -c foo.nc
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228       Produce  an  annotated  CDL  version  of  the structure and data in the
229       netCDF file `foo.nc', using C-style indexing for the annotations:
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231              ncdump -b c foo.nc > foo.cdl
232
233       Output data for only the variables `uwind' and `vwind' from the  netCDF
234       file `foo.nc', and show the floating-point data with only three signif‐
235       icant digits of precision:
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237              ncdump -v uwind,vwind -p 3 foo.nc
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239       Produce a fully-annotated (one data value per line) listing of the data
240       for  the  variable  `omega', using Fortran conventions for indices, and
241       changing the netCDF dataset name in the resulting CDL file to `omega':
242
243              ncdump -v omega -f fortran -n omega foo.nc > Z.cdl
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SEE ALSO

246       ncgen(1), netcdf(3)
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BUGS

249       Character arrays that contain a null-byte are treated like  C  strings,
250       so no characters after the null byte appear in the output.
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252       Multidimensional  character  string  arrays are not handled well, since
253       the CDL syntax for breaking a long character string into several short‐
254       er lines is weak.
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256       There  should  be a way to specify that the data should be displayed in
257       `record' order, that is with the all the values for `record'  variables
258       together that have the same value of the record dimension.
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262Release 4.2                       2012-03-08                         NCDUMP(1)
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