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Go Formatter

The Go Formatter library implements replacement fields surrounded by curly braces {} format strings.

[[TOC]]

Features

  • Format string by providing arguments without using placeholders or format verbs %
  • Format string using automatic placeholder {p}
  • Format string using positional placeholders {pN}
  • Format string using named placeholders {name}
  • Format string using object placeholders {.Field}, {p.Field} and {pN.Field} where Field is an exported struct field or method
  • Use custom placeholder string. Default is p
  • Use custom replacement delimiters. Default are { and }
  • Use custom replacement functions with transformation using pipeline |
  • Many different handy built-in functions {name}
  • Support for text colorization using {color}, {rgb}, {bright}, {background} and so on
  • Support for setting text attributes like bold, italic, strike, blink and so on
  • Support for getting OS values like {ip}, {user}, {hostname}, {cwd}, {pid}, {env} and so on
  • Support for getting and formatting time using {now}, {rfc3339}, {iso8601} and so on
  • Support for string transformation using {lower}, {upper}, {capitalize} and so on
  • Support for path transformation using {absolute}, {base}, {directory}, {clean}, {extension} and so on
  • Support for object formatting using {fields}, {json}, {indent} and so on
  • Auto ANSI escape sequences detection and forcing it using the FORCE_ESCAPE_SEQUENCES environment variable
  • Under the hood it uses the standard text/template package

Usage

Import formatter package:

import "gitlab.com/tymonx/go-formatter/formatter"

Without arguments

formatted, err := formatter.Format("Without arguments")

fmt.Println(formatted)

Output:

Without arguments

With arguments

formatted, err := formatter.Format("With arguments", 3, nil, 4.5, true, "arg1", []byte{}, Error("error"))

fmt.Println(formatted)

Output:

With arguments 3 <nil> 4.5 true arg1 [] error

Automatic placeholder

formatted, err := formatter.Format("Automatic placeholder {p}:{p}:{p}():", "dir/file", 1, "func1")

fmt.Println(formatted)

Output:

Automatic placeholder dir/file:1:func1():

Positional placeholders

formatted, err := formatter.Format("Positional placeholders {p1}:{p0}:{p2}():", 2, "dir/file", "func1")

fmt.Println(formatted)

Output:

Positional placeholders dir/file:2:func1():

Named placeholders

formatted, err := formatter.Format("Named placeholders {file}:{line}:{function}():", formatter.Named{
    "line":     3,
    "function": "func1",
    "file":     "dir/file",
})

fmt.Println(formatted)

Output:

Named placeholders dir/file:3:func1():

Object placeholders

It handles exported struct fields and methods. First letter must be capitalized. Transformation using pipeline | also works with exported struct fields and struct methods. For more information about pipelines please see the Pipelines section from the standard text/template package.

object := struct {
    Line     int
    Function string
    File     string
}{
    Line:     4,
    Function: "func1",
    File:     "dir/file",
}

formatted, err := formatter.Format("Object placeholders {.File}:{.Line}:{.Function}():", object)

fmt.Println(formatted)

Output:

Object placeholders dir/file:4:func1():

Object with automatic placeholder

It handles exported struct fields and methods. First letter must be capitalized. Transformation using pipeline | also works with exported struct fields and struct methods. For more information about pipelines please see the Pipelines section from the standard text/template package.

object1 := struct {
    Message string
}{
    Message: "object1",
}

object2 := struct {
    X int
}{
    X: 2,
}

formatted, err := formatter.Format("Object with automatic placeholder {p.Message} {p.X}", object1, object2)

fmt.Println(formatted)

Output:

Object with automatic placeholder object1 2

Object with positional placeholders

It handles exported struct fields and methods. First letter must be capitalized. Transformation using pipeline | also works with exported struct fields and struct methods. For more information about pipelines please see the Pipelines section from the standard text/template package.

object1 := struct {
    Message string
}{
    Message: "object1",
}

object2 := struct {
    X int
}{
    X: 2,
}

formatted, err := formatter.Format("Object with positional placeholders {p1.X} {p0.Message}", object1, object2)

fmt.Println(formatted)

Output:

Object with positional placeholders 2 object1

Mixed placeholders

objectPointer := &struct {
    X int
    Y int
    Z int
}{
    X: 2,
    Z: 6,
    Y: 3,
}

formatted, err := formatter.Format("Mixed placeholders {.X}.{p}.{.Y}.{.Z} {p1} {p0}", objectPointer, "b", "c", nil)

fmt.Println(formatted)

Output:

Mixed placeholders 2.{2 3 6}.3.6 b {2 3 6} c <nil>

Writer

var buffer bytes.Buffer

err := formatter.FormatWriter(&buffer, "Writer {p2}", 3, "foo", "bar")

fmt.Println(buffer.String())

Output:

Writer bar 3 foo

Functions

Transformation using pipeline | also works with exported struct fields and struct methods. For more information about pipelines please see the Pipelines section from the standard text/template package.

functions := formatter.Functions{
    "str": func() string {
        return "text"
    },
    "number": func() int {
        return 3
    },
    "boolean": func() bool {
        return true
    },
    "floating": func() float64 {
        return 4.5
    },
    "transform": func(value int) int {
        return value + 3
    },
}

formatted, err := formatter.New().SetFunctions(functions).
    Format("Custom functions {str} {p} {number} {boolean} {floating} {number | transform}", 5)

fmt.Println(formatted)

Output:

Custom functions text 5 3 true 4.5 6

Custom placeholder

formatted, err := formatter.New().SetPlaceholder("arg").Format("Custom placeholder {arg1} {arg0}", "2", 3)

fmt.Println(formatted)

Output:

Custom placeholder 3 2

Custom delimiters

formatted, err := formatter.New().SetDelimiters("<", ">").Format("Custom delimiters <p1> <p0>", "4", 3)

fmt.Println(formatted)

Output:

Custom delimiters 3 4

Must format

fmt.Println(formatter.MustFormat("With arguments", 3, nil, false, 4.5, "text", []byte{}, Error("error")))

Output:

With arguments 3 <nil> false 4.5 text [] error

Colors

Standard:

formatted, err := formatter.Format("With colors {red}red{normal} {green}green{normal} {blue}blue{normal}")

fmt.Println(formatted)

Bright:

formatted, err := formatter.Format("With bright colors {magenta | bright}magenta{normal}")

fmt.Println(formatted)

Background:

formatted, err := formatter.Format("With background colors {yellow | background}yellow{normal}")

fmt.Println(formatted)

Background + bright:

formatted, err := formatter.Format("With background bright colors {cyan | bright | background}cyan{normal}")

fmt.Println(formatted)

RGB:

formatted, err := formatter.Format("With RGB {rgb 255 165 0}funky{normal}")

fmt.Println(formatted)

Background RGB:

formatted, err := formatter.Format("With background RGB {rgb 255 165 0 | background}funky{normal}")

fmt.Println(formatted)

Built-in functions

For more details please see the formatter package documentation.

Run example:

go run ./examples/functions/

Output:

Example

Overriding ANSI escape sequences detection

By default, the formatter package determines whether or not to use ANSI escape sequences based on whether it's connected to a TTY or not. This works for most use cases, but may not behave as expected if you use the formatter package in a pipeline of commands, where STDOUT is being piped to another command.

To force it, add FORCE_ESCAPE_SEQUENCES=1 to the environment you're running in. For example:

FORCE_ESCAPE_SEQUENCES=1 ./app | tee output.log

Supported values for the FORCE_ESCAPE_SEQUENCES environment variable:

  • To force enable: 1, true, enable, on, yes, y
  • To force disable: 0, false, disable, off, no, n
  • Auto detection when variable is unset, empty or contains other values