A mini-framework to create complex cli. Inspired by Python argparse.
Warning This project is no longer maintained, because argparse is now a part of Erlang/OTP: https://www.erlang.org/doc/man/argparse.html (starting with OTP 26).
To accommodate with this change,
argparse
module has been renamed toargs
in version 2.0.0. Applications that needargparse
for earlier OTP versions can use this library until the lowest supported version is OTP 26, and then just move forward toargparse
provided by OTP.There are minor differences in the command line options description between
args
and OTPargparse
:
int
type is renamedinteger
- exceptions are accompanied by extended error information
Follows conventions of Unix Utility Argument Syntax.
argparse [-abcDxyz][-p arg][operand]
Converts list of strings (command line) into an argument map,and a command path; see argparse reference for detailed description.
Make a step beyond parser, and export existing Erlang functions: cli reference
Basic example
cli is naturally suitable for building small escript-based apps:
#!/usr/bin/env escript
-export([main/1, cli/0, rm/1]).
-behaviour(cli).
-mode(compile). %% evaluated module cannot contain callbacks
main(Args) ->
cli:run(Args, #{progname => "simple"}).
cli() ->
#{
handler => {?MODULE, rm},
arguments => [
#{name => force, short => $f, type => boolean, default => false},
#{name => recursive, short => $r, type => boolean, default => false},
#{name => dir}
]}.
rm(#{force := Force, recursive := Recursive, dir := Dir}) ->
io:format("Removing ~s (force ~s, recursive: ~s)~n",
[Dir, Force, Recursive]).
The example above does not have sub-commands, and implements rm/1
handler, that serves as an entry point with parsed arguments. Help options are
added automatically:
$ ./erm --help
usage: erm [-fr] <dir>
Optional arguments:
dir
-r recursive, [false]
-f force, [false]
Calc: cli with multiple commands
Calculator implements several commands, with sub-commands available. Full source code here: doc/examples/escript/calc
Command definitions:
cli() ->
#{
commands => #{
"sum" => #{
arguments => [
#{name => num, nargs => nonempty_list, type => int, help => "Numbers to sum"}
]
},
"math" => #{
commands => #{
"sin" => #{handler => {math, sin, undefined}},
"cos" => #{},
"tan" => #{handler => {math, tan, undefined}}
},
arguments => [
#{name => in, type => float, help => "Input value"}
]
},
"mul" => #{
arguments => [
#{name => left, type => int},
#{name => right, type => int}
]
}
}
}.
The calculator provides "sum" command that prints a sum of integer numbers:
$ ./calc sum 1 2 3
6
Math sub-commands provide trigonometric functions:
$ ./calc math cos 1.4
0.16996714290024104
$ ./calc math sin 1.4
0.9854497299884601
cli is capable of handling releases containing hundreds of modules implementing cli behaviour. Commands may be exported from multiple modules and applications. cli makes best efforts to merge commands exported, format usage output and error messages.
See example: doc/examples/multi
This example contains two modules, multi_math.erl and multi_string.erl.
Use rebar3 escriptize
to build the application. Try various commands,
e.g. ./multi math cos 1.0
, or ./multi string lexemes 1+2+3+4 -s +
to get a feeling!
Argument parser alone
It is possible to use argument parser alone, without the cli mini-framework:
#!/usr/bin/env escript
main(Args) ->
#{force := Force, recursive := Recursive, dir := Dir} =
args:parse(Args, cli()),
io:format("Removing ~s (force: ~s, recursive: ~s)~n",
[Dir, Force, Recursive]).
cli() ->
#{arguments => [
#{name => force, short => $f, type => boolean, default => false},
#{name => recursive, short => $r, type => boolean, default => false},
#{name => dir}
]}.
cli automatically prints usage, if command line parser reports an error. An attempt is made to guess the most relevant command. Argument help can be customised.
This project requires OTP-22 or above. Simple integration is available via Hex and rebar3.
{deps, [argparse]}.
In comparison with Python implementation, argparse
for Erlang:
- boolean flag (option) automatically uses {store, true}
- all positional arguments are required by default (even when nargs is 'maybe')
- first-class (sub) commands, slightly differently from argparse
- implicit --help/-h is not a part of argparse (but implemented in cli)
Commands vs. positional arguments: command always takes precedence over a positional argument. Commands form exclusive groups, e.g. only one command can be followed at a time.
- command (priority positional argument) : ectl {crawler|reader|writer}
- command, and sub-command: ectl crawler {start|stop|check}
- positional argument (required): ectl
- positional argument (with default): ectl []
- boolean flag: ectl [-rf]
- required flag: ectl -r
- short optional argument: ectl [-i ]
- short optional: ectl [-i []]
- required short option: ectl -i
- long option flag: ectl [--foo]
- long optional argument: ectl [--foo ]
- required long: ectl --foo
- long, arg=value form: ectl --foo=arg
- list of arguments: ectl , ...
To be considered after 1.2.0:
- search for commands and arguments (mini-man)
- abbreviated long forms
- mutual exclusion groups
- shell auto-complete
- automatically generated negative boolean long forms "--no-XXXX"