Go CLI Output

Go CLI Output

Every line a CLI Only tool prints goes through utils, which renders it two ways depending on whether --debug is set, and drops its own color whenever stdout is not a terminal.

Web Only and Headless API Service projects have no utils/ package. They log through the same zerolog setup and print nothing else, since a container's stdout has no reader to style output for.

The Two Tiers

There is no third tier for a machine reading the output, and a flag that asks for one is not added. An agent invoking the tool passes --debug and gets more than a plain-text mode could carry: every step announced, every wrapped error intact, and nothing redrawn over.

Piped Output

Plain text is a property of the destination rather than a mode the caller selects. Every printer writes through lipgloss.Println, whose writer is colorprofile.NewWriter(os.Stdout, os.Environ()); that resolves to NoTTY when stdout is not a terminal and strips every escape sequence on the way out. Piping the tool anywhere produces plain text with nothing passed and nothing remembered.

zerolog answers the same check one level up, choosing the writer rather than decolorizing one: ConsoleWriter on a terminal, and its own JSON otherwise.

var out io.Writer = os.Stdout
if StdoutIsTerminal {
    out = zerolog.ConsoleWriter{Out: os.Stdout, TimeFormat: time.DateTime}
}
log.Logger = zerolog.New(out).With().Timestamp().Logger()

Ephemeral output is a terminal affordance and nothing else. ClearLines and the in-place progress bar are inert under --debug and whenever stdout is not a terminal, so a log or a pipe keeps the full progression rather than a stream of cursor escapes.

Globals

package utils

import (
    "os"

    "github.com/charmbracelet/x/term"
)

var GlobalDebugFlag bool

var (
    StdinIsTerminal  = term.IsTerminal(os.Stdin.Fd())
    StdoutIsTerminal = term.IsTerminal(os.Stdout.Fd())
)

term.IsTerminal rather than os.ModeCharDevice: /dev/null is a character device, so the mode bit reports a terminal for the one stream that most certainly has nobody at it, and a prompt gated on it then opens a TUI into the void. The module already ships under the bubbletea and lipgloss stack, so using it directly adds no build.

Both are evaluated once at package init, since neither stream is replaced underneath a running process.

The Print Shape

Every printer branches the same way, debug first and styled output otherwise. Writing them all to one shape means a new printer is a copy with a different glyph rather than a new decision.

var (
    infoStyle    = lipgloss.NewStyle().Foreground(lipgloss.ANSIColor(12)) // bright blue
    successStyle = lipgloss.NewStyle().Foreground(lipgloss.ANSIColor(10)) // bright green
    errorStyle   = lipgloss.NewStyle().Foreground(lipgloss.ANSIColor(9))  // bright red
    warnStyle    = lipgloss.NewStyle().Foreground(lipgloss.ANSIColor(11)) // bright yellow
)

func PrintInfo(msg string) {
    if GlobalDebugFlag {
        log.Info().Msg(msg)
        return
    }
    lipgloss.Println(infoStyle.Render("→ " + msg))
}

func PrintError(msg string, err error) {
    if GlobalDebugFlag {
        if err != nil {
            log.Error().Err(err).Msg(msg)
        } else {
            log.Error().Msg(msg)
        }
        return
    }
    lipgloss.Println(errorStyle.Render("✗ " + msg))
}

func PrintFatal(msg string, err error) {
    PrintError(msg, err)
    os.Exit(1)
}

fmt.Println never appears in a printer, since it writes past the color profile and leaves escape sequences in a piped stream.

The Print Surface

PrintGeneric adds no prefix, no glyph, and no style, because data the caller wants verbatim (a URL, a token, a rendered table) must not gain a marker that a consumer then has to strip.

PrintFatal exits with status 1 after printing, so a caller never has to remember the os.Exit that a fatal message implies.

Error Discipline

The msg parameter is the human-readable label, and err is the Go error. Passing the actual err in the error parameter is what makes --debug useful, since zerolog's .Err(err) records it as a structured field that a baked-in string cannot become.

Normal output shows only msg. The error detail is exclusively for debug introspection, which keeps a stack of wrapped errors out of a user's face while leaving it one flag away.

utils.PrintFatal("git not found in PATH", err)
utils.PrintIndentedError(toolName, result.Err)

Passing nil for err is correct only when there genuinely is no underlying error: a validation failure, a summary line, an informational warning.

Subprocess Errors

A direct exec.Command that fails returns "exit status 1" and nothing else, so capture stderr into the error before printing it, or the debug tier records a message with no cause.

cmd := exec.Command("sudo", "cp", src, dst)
var stderr strings.Builder
cmd.Stderr = &stderr
if err := cmd.Run(); err != nil {
    if detail := strings.TrimSpace(stderr.String()); detail != "" {
        err = fmt.Errorf("%s: %w", detail, err)
    }
    utils.PrintFatal("failed to copy binary", err)
}

A helper that already captures both streams into the returned error needs none of this.

Terminal Colors

Colors are ANSI indices 0 through 15, never hex. An index is remapped by the user's terminal theme, so the same tool reads correctly under Dracula, Catppuccin, Solarized, or a scheme nobody has published; a hex value overrides that theme and fights it. Bright variants, 8 through 15, are preferred for foreground text.

var (
    ColorBlue    = lipgloss.ANSIColor(12) // bright blue
    ColorGreen   = lipgloss.ANSIColor(10) // bright green
    ColorRed     = lipgloss.ANSIColor(9)  // bright red
    ColorYellow  = lipgloss.ANSIColor(11) // bright yellow
    ColorMagenta = lipgloss.ANSIColor(13) // bright magenta
    ColorCyan    = lipgloss.ANSIColor(14) // bright cyan
    ColorFg      = lipgloss.ANSIColor(15) // bright white, primary text
    ColorMuted   = lipgloss.ANSIColor(7)  // white, secondary text
    ColorChrome  = lipgloss.ANSIColor(8)  // bright black, borders and dim UI
)

Tables

PrintTable(headers, rows) renders one way, as lipgloss box drawing. Box characters are not escape sequences, so a piped table arrives intact with only its colors stripped, and a second renderer for a second audience would be a format nobody validates.

package utils

import (
    "charm.land/lipgloss/v2"
    "charm.land/lipgloss/v2/table"
)

var (
    headerStyle = lipgloss.NewStyle().Bold(true).Foreground(ColorFg).Padding(0, 1)
    cellStyle   = lipgloss.NewStyle().Foreground(ColorMuted).Padding(0, 1)
    borderStyle = lipgloss.NewStyle().Foreground(ColorChrome)
)

func PrintTable(headers []string, rows [][]string) {
    t := table.New().
        Border(lipgloss.NormalBorder()).
        BorderStyle(borderStyle).
        Headers(headers...).
        Rows(rows...).
        StyleFunc(func(row, col int) lipgloss.Style {
            if row == table.HeaderRow {
                return headerStyle
            }
            return cellStyle
        })
    PrintGeneric(t.Render())
}

A command whose output is meant to be parsed rather than read takes a --json flag and marshals a struct, which is a data contract instead of a table someone has to scrape.