myflags

myflags

myflags is a Golang module to make command line flag easier, it creates command line flags based on fields in a struct, so user doesn't need to manually create the flags one by one. it also supports more types than flag module, and easily extensible for new types, user could even add support for existing type without using alias type.

myflags also support multiple and hierarchical actions, each action could have a set of its own parameters and sub-actions, for example a file compression tool cptool could have "compress" and "extract" action, and each has different parameters, and "compress" could have sub-actions like "zipfoler" and "zipfile", each then again has different parameters.

Input wise, parameters of an action has prefix "-", while action doesn't have any prefix.

for example, compress a folder could be command line input like cptool compress -profile <profile_name> zipfolder -foldername <foldername>.

Struct Field Tags

Following struct field tags are supported:

• skipflag: skip the field for flagging
• alias: use the specified alias as the name of the parameter
• usage: the usage string of the parameter
• action: this field is an action

Quick Start

Using myflags is straight forward:

1. define all flags in a struct, each action is a field whose type is another struct.
2. create a Filler with the struct, call Fill method with the struct variable with default value.
3. call flag.Parse()

Following is an example: https://github.com/hujun-open/myflags/blob/2fd27463cabdc368b87aecc7addbb42f5535abc6/example/main.go#L1-L45 the created flags:

.\cptool.exe -?
a zip command
  - configfile: working profile
        default:default.conf
  = compress: to compress things
    - loop: number of compress iterations
        default:0x20
    - profile:
    - s:
        default:false
    = dryrun: dry run, doesn't actually create any file
    = zipfolder: zip a folder
      - folder: specify folder name
    = zipfile: zip a file
      - f: specify file name
        default:defaultzip.file
  = extract: to unzip things
    - inputfile: input zip file
  = help: help

some parsing results:

.\cptool.exe -configfile cp.conf compress -profile my.profile -s zipfilder -folder ./bigfolder/
parsed actions [Compress]
{ConfigFile:cp.conf Compress:{Loop:32 Profile:my.profile Skip:true NoFlag: DryRun:{} ZipFolder:{FolderName:} ZipFile:{FileName:defaultzip.file}} Extract:{InputFile:} Help:{}}

.\cptool.exe -configfile cp.conf compress -loop 100 dryrun
parsed actions [Compress DryRun]
{ConfigFile:cp.conf Compress:{Loop:100 Profile: Skip:false NoFlag: DryRun:{} ZipFolder:{FolderName:} ZipFile:{FileName:defaultzip.file}} Extract:{InputFile:} Help:{}}

Supported Types

Base:

• all int/uint types: support base tag for the base
• float32/float64
• string
• bool
• time.Duration
• time.Time: supports layout tag for time layout string
• All types implement both of following interface:
  • encoding.TextUnmarshaler
  • encoding.TextUnmarshaler
• All type register via myflags.Register function

Note: flag is only created for exported struct field.

In addition to base types, following types are also supported:

• pointer to the base type
• slice/array of base type
• slice/array of pointer to the base type

for slice/array, use "," as separator.

myflags also supports following type of struct:

• nested struct, like:

type Outer struct {
    Nested struct {
        Name string
    }
}

• embeded struct, like:

type SubS struct {
    SubName string
}
type Outer struct {
    SubS
}

Flag Naming

By default, the name of created flag is the lowercase of struct field name, in case the field is part of sub-struct, and parent struct is NOT an action, then the name of created flag is "<parent_field_name>-<field_name>";

Optionally a renaming function could be supplied when creating the Filler, myflags uses the renaming function returned string as the flag name.

Extension

New type could be supported via myflags.Register, which takes a variable implements myflags.RegisteredConverters interface. the myflags.Register must be called before myflags.Fill, typically it should be called in init().

Check time.go, inttype.go for examples.

Bool

myflags use standard Golang module flag, which doesn't support "-flag x" format for bool. using "-flag x" for bool could cause silent failure that input parameters after bool don't get parsed.