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This module provides the standard Nim command line parser. It supports one convenience iterator over all command line options and some lower-level features.

Supported Syntax

The following syntax is supported when arguments for the shortNoVal and longNoVal parameters, which are described later, are not provided:

1. Short options: -abcd, -e:5, -e=5
2. Long options: --foo:bar, --foo=bar, --foo
3. Arguments: everything that does not start with a -

These three kinds of tokens are enumerated in the CmdLineKind enum.

When option values begin with ':' or '=', they need to be doubled up (as in --delim::) or alternated (as in --delim=:).

The -- option, commonly used to denote that every token that follows is an argument, is interpreted as a long option, and its name is the empty string.

Parsing

Use an OptParser to parse command line options. It can be created with initOptParser, and next advances the parser by one token.

For each token, the parser's kind, key, and val fields give information about that token. If the token is a long or short option, key is the option's name, and val is either the option's value, if provided, or the empty string. For arguments, the key field contains the argument itself, and val is unused. To check if the end of the command line has been reached, check if kind is equal to cmdEnd.

Here is an example:

import std/parseopt

var p = initOptParser("-ab -e:5 --foo --bar=20 file.txt")
while true:
  p.next()
  case p.kind
  of cmdEnd: break
  of cmdShortOption, cmdLongOption:
    if p.val == "":
      echo "Option: ", p.key
    else:
      echo "Option and value: ", p.key, ", ", p.val
  of cmdArgument:
    echo "Argument: ", p.key

# Output:
# Option: a
# Option: b
# Option and value: e, 5
# Option: foo
# Option and value: bar, 20
# Argument: file.txt

The getopt iterator, which is provided for convenience, can be used to iterate through all command line options as well.

To set a default value for a variable assigned through getopt and accept arguments from the cmd line. Assign the default value to a variable before parsing. Then set the variable to the new value while parsing.

Here is an example: .. code-block:: import std/parseopt

var varName: string = "defaultValue"

for kind, key, val in getopt(): case kind of cmdArgument: discard of cmdLongOption, cmdShortOption: case key: of "varName": # --varName:<value> in the console when executing varName = val # do input sanitization in production systems of cmdEnd: discard

shortNoVal and longNoVal

The optional shortNoVal and longNoVal parameters present in initOptParser are for specifying which short and long options do not accept values.

When shortNoVal is non-empty, users are not required to separate short options and their values with a ':' or '=' since the parser knows which options accept values and which ones do not. This behavior also applies for long options if longNoVal is non-empty. For short options, -j4 becomes supported syntax, and for long options, --foo bar becomes supported. This is in addition to the previously mentioned syntax. Users can still separate options and their values with ':' or '=', but that becomes optional.

As more options which do not accept values are added to your program, remember to amend shortNoVal and longNoVal accordingly.

The following example illustrates the difference between having an empty shortNoVal and longNoVal, which is the default, and providing arguments for those two parameters:

import std/parseopt

proc printToken(kind: CmdLineKind, key: string, val: string) =
  case kind
  of cmdEnd: doAssert(false)  # Doesn't happen with getopt()
  of cmdShortOption, cmdLongOption:
    if val == "":
      echo "Option: ", key
    else:
      echo "Option and value: ", key, ", ", val
  of cmdArgument:
    echo "Argument: ", key

let cmdLine = "-j4 --first bar"

var emptyNoVal = initOptParser(cmdLine)
for kind, key, val in emptyNoVal.getopt():
  printToken(kind, key, val)

# Output:
# Option: j
# Option: 4
# Option: first
# Argument: bar

var withNoVal = initOptParser(cmdLine, shortNoVal = {'c'},
                              longNoVal = @["second"])
for kind, key, val in withNoVal.getopt():
  printToken(kind, key, val)

# Output:
# Option and value: j, 4
# Option and value: first, bar

See also

• os module for lower-level command line parsing procs
• parseutils module for helpers that parse tokens, numbers, identifiers, etc.
• strutils module for common string handling operations
• json module for a JSON parser
• parsecfg module for a configuration file parser
• parsecsv module for a simple CSV (comma separated value) parser
• parsexml module for a XML / HTML parser
• other parsers for more parsers