klo

klo is a Go package for kubectl-like output of Go values (such as structs, maps, et cetera) in several output formats. You might want to use this package in your CLI tools to easily offer kubectl-like output formatting to your Kubernetes-spoiled users.

The Only True Go Way mandates package names to be short, concise, evocative. Thus, the package name klo was chosen to represent the essence of kubectl-like output in a manner as short, concise and evocative as ever. If you happen to have sanitary associations, then better flush them now.

Supported Output Formats

The following output formats are supported:

• ASCII columns, which optionally can be customized (-o custom-columns= and -o custom-columns-file=).
  • optional sorting by specific column(s) using JSONPath expressions.
• JSON and JSONPath-customized (-o json, -o jsonpath=, and -o jsonpath-file=).
• YAML (-o yaml).
• Go templates (-o go-template= and -o go-template-file=).

Note: -o name and -o wide are application-specific and are basically customized ASCII column formats, with just varying custom column configurations. Thus, they can be easily implemented in your appliaction itself and then use the existing klo package features.

In addition, sorting is supported by wrapping an output-format printer into a sorting printer. This allows to sort the rows in a custom-columns output based on row values taken from one or even multiple columns.

Basic Usage

The following code example prints a table with multiple columns, and the rows sorted by the NAME column.

import (
    "os"
    "github.com/thediveo/klo"
)

func main() {
    // Some data structure we want to print in tables.
    type myobj struct {
        Name string
        Foo  int
        Bar  string
    }
    // A slice of objects we want to print as a table with custom columns.
    list := []myobj{
        myobj{Name: "One", Foo: 42},
        myobj{Name: "Two", Foo: 666, Bar: "Bar"},
        myobj{Name: "Another Two", Foo: 123, Bar: "Bar"},
    }
    // Create a table printer with custom columns, to be filled from fields
    // of the objects (namely, Name, Foo, and Bar fields).
    prn, err := klo.PrinterFromFlag("",
        &klo.Specs{DefaultColumnSpec: "NAME:{.Name},FOO:{.Foo},BAR:{.Bar}"})
    if err != nil {
        panic(err)
    }
    // Use a table sorter and tell it to sort by the Name field of our column objects.
    table, err := klo.NewSortingPrinter("{.Name}", prn)
    if err != nil {
        panic(err)
    }
    table.Fprint(os.Stdout, list)

This will output:

NAME        FOO  BAR
Another Two 123  Bar
One         42
Two         666  Bar

In addition, NewGoTemplatePrinterWithFuncs allows providing template functions.

-o Usage

For supporting "-o" output format control via CLI args, choose any CLI arg handling package you like, such as flag, pflag, cobra, et cetera. Then, call PrinterFromFlag(oflagvalue, &myspecs), where oflagvalue is the set/default value of the CLI arg you use for controlling the output format in your own app's CLI. Your myspecs should specify the default custom-columns format, and optionally a wide custom-clumns format variant. If you support go templates for output formatting, then you should also pass in the value of your --template= CLI arg.

import (
    "github.com/thediveo/klo"
)

func main() {
    // Get your -o and -template flag values depending on your CLI arg toolkit.
    templateflagvalue := ""
    oflagvalue := "wide"
    // Set up the specs and get a suitable output formatting printer according
    // to the specific output format choosen and the auxiliary information given
    // on specs and an optional Go template arg.
    myspecs := klo.Specs{
        DefaultColumnSpec: "FOO:{.Foo}",
        WideColumnSpec: "FOO:{.Foo},BAR:{.Bar}",
        GoTemplateArg: templateflagvalue,
    }
    prn, err := PrinterFromFlag(oflagvalue, &myspecs)
    //...
}

Supported Go Versions

klo supports versions of Go that are noted by the Go release policy, that is, major versions N and N-1 (where N is the current major version).

Copyright and License

klo is Copyright 2019–2024 Harald Albrecht, and licensed under the Apache License, Version 2.0.