nml

A query/modify utility for Fortran namelists

Build

To create an executable uberjar:

Install Clojure if you do not already have it. You can use the installer's --prefix option to specify any installation location that works for you.
Add your Clojure installation's bin/ directory to your PATH and ensure that clj --help runs successfully.
Run make uberjar.

You should now be able to run java -jar target/nml.jar --help for a usage synopsis.

Alternatively, you may leverage GraalVM to build a native executable:

Download and extract the GraalVM release matching your OS and Java version. (A successful build was last done with GraalVM Community Edition 22.3.3 on Linux with Java 11.)
Export environment variable GRAALVM pointing to the extracted directory's root.
Run $GRAALVM/bin/gu install native-image to install GraalVM's native-image tool.
Run make native. This may take some time.

You should now have an nml native executable in this directory.

Test

Run make test.

The Fortran program test/nml_test.f90 may be used to verify the validity of the test namelist file test/nl.in. Compile and run like e.g.

$ gfortran -g nml_test.f90 && ./a.out

Run

Running either java -jar target/nml.jar, or the nml native executable, with the --help flag:

Usage: nml [options]

Options:

  -c, --create      Create new namelist file
  -e, --edit file   Edit file (instead of '-i file -o file')
  -f, --format fmt  Output in format 'fmt' (default: namelist)
  -g, --get n:k     Get value of key 'k' in namelist 'n'
  -h, --help        Show usage information
  -i, --in file     Input file (default: stdin)
  -k, --keep-order  Keep namelists in original order
  -n, --no-prefix   Report values without 'namelist:key=' prefix
  -o, --out file    Output file (default: stdout)
  -s, --set n:k=v   Set value of key 'k' in namelist 'n' to 'v'
  -v, --version     Show version information

Valid output formats are: bash, json, ksh, namelist

Examples

Assume that the contents of a file nl are as follows:

&b
  L = .TRUE. ! logical value
  c=( 3.142 , 2.718)
  ! This is a comment.
  i=88
/

&a r=1.1e8, S = 'Hello World' r=2.2e8 /

This junk isn't in a namelist.

By default, nml reads from stdin and writes to stdout and, with no command-line options specified, prints a simplified, sorted version of the input:

% cat nl | nml
&a
  r=2.2e8
  s='Hello World'
/
&b
  c=(3.142,2.718)
  i=88
  l=t
/

Note that nml normalizes many formatting options:

Whitespace and comments are removed.
Non-string text is presented in lower-case.
Key-value pairs are printed one-per-line without comma separators.
Logical values are represented in their simplest form.

You may supply the -k/--keep-order flag to have nml output namelists in the same order in which they were read.

The --in and --out options can be used to specify input and output files, respectively.

Querying

To get values:

% nml --in nl --get a:r --get b:i
a:r=2.2e8
b:i=88

To print only values, without namelist:key= prefixes:

% nml --in nl --no-prefix --get b:i --get a:r
88
2.2e8

Note that values are printed in the order they were requested on the command line.

An obvious application is to use nml to insert namelist settings in scripts:

% cat say.sh
#!/bin/sh
echo "The value of i is $(nml --in nl --no-prefix --get b:i)"

% ./say.sh
The value of i is 88

If any requested namelists or keys are not found, nml reports the first ungettable value and exits with error status:

% nml --in nl --get a:r --get b:x || echo "FAIL"
nml: b:x not found
FAIL

Modifying

To set (or add) values:

% nml --in nl --set a:s="'Hi'" --set b:x=.false. --set c:z=99
&a
  r=2.2e8
  s='Hi'
/
&b
  c=(3.142,2.718)
  i=88
  l=t
  x=f
/
&c
  z=99
/

Note that get and set commands may not be mixed in a single nml invocation.

A file may be edited in place with the --edit command (equivalent, in this case, to --in nl --out nl):

% nml --in nl --get a:s
a:s='Hello World'

% nml --edit nl --set a:s="'Hi'"

% nml --in nl --get a:s
a:s='Hi'

To create a new namelist file from scratch (i.e. without starting with an input file):

% rm -f new

% nml --create --out new --set a:x=77 --set a:y=88

% cat new
&a
  x=77
  y=88
/

Output Format

In addition to the default Fortran namelist output format, nml can output namelist data as a bash/ksh function, or as JSON data.

The bash/ksh function allows fast lookups in shell scripts after a single nml invocation, via the defined nmlquery shell function.

% eval "$(nml --in nl --format bash)"

% nmlquery a s
'Hi'

% nmlquery b c
(3.142,2.718)

Example JSON output:

% nml --in nl --format json
{"b":{"l":true, "c":"(3.142,2.718)", "i":88},
 "a":{"r":2.2E8, "s":"Hello World"}}

Note that several valid Fortran namelist values, e.g. r*c repeat values like 10*'c', or complex literals like (1.2,3.4) are represented as strings in JSON for lack of native support.

Limitations

Standards support

nml tries to conform to Fortran 2008 section 10.11 "Namelist formatting", though no explicit attempt has been made to support object-oriented constructs. The standard permits all sorts of nonsense that ought, for sanity's sake, to be prohibited; compilers make matters worse by apparently allowing further, non-conformant nonsense. I would be grateful for bug reports describing non-conformant nml behavior, but please confirm that your namelist is conformant before filing a ticket or PR.

Repeated namelists

The Fortran standard allows namelist files like this:

&nl v = 77 /
&nl v = 88 /

With the namelist file open, a first Fortran read statement would set v to 77, and the second would set it to 88. This use case is not supported by nml. Rather, the last of a set of same-named namelists will override previous ones, and nml will output a single nl namelist with the final values.

Currently, nml does not (TODO: but should) correctly support this variant of the above:

&nl v = 77 /
&nl w = 88 /

The correct behavior would be to merge the contents of the two same-named namelists, providing values for both v and w.

Semicolon as value separator

The use of the semicolon as a value separator (in COMMA decimal edit mode, rather than POINT decimal edit mode -- see Fortran 2008 standard section 10.10.2), is not currently supported.

Thanks

Thanks to Mark Engelberg for the wonderful Instaparse, on which nml is based.