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v/vlib/flag/README.md

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## Description:
The `flag` module is a command line option parser.
Its main features are:
- simplicity of usage.
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- parses flags like `-f` or '--flag' or '--stuff=things' or '--things stuff'.
- handles bool, int, float and string args.
- can print usage information listing all the declared flags.
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- handles unknown arguments as error.
See also the `cli` module, for a more complex command line option parser,
that supports declaring multiple subcommands each having a separate set of
options.
Usage example:
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```v
module main
import os
import flag
fn main() {
mut fp := flag.new_flag_parser(os.args)
fp.application('flag_example_tool')
fp.version('v0.0.1')
fp.limit_free_args(0, 0)? // comment this, if you expect arbitrary texts after the options
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fp.description('This tool is only designed to show how the flag lib is working')
fp.skip_executable()
an_int := fp.int('an_int', 0, 0o123, 'some int to define 0o123 is its default value')
a_bool := fp.bool('a_bool', 0, false, 'some boolean flag. --a_bool will set it to true.')
a_float := fp.float('a_float', 0, 1.0, 'some floating point value, by default 1.0 .')
a_string := fp.string('a_string', `a`, 'no text', 'finally, some text with ' +
' `-a` as an abbreviation, so you can pass --a_string abc or just -a abc')
additional_args := fp.finalize() or {
eprintln(err)
println(fp.usage())
return
}
println('an_int: ${an_int} | a_bool: ${a_bool} | a_float: ${a_float} | a_string: "${a_string}" ')
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println(additional_args.join_lines())
}
```