feat(pagination): implement paginated output

Implement a `pager` config option. If configured, `cheat` will
automatically pipe output through the configured pager (where
appropriate).

cmd/cheat/cmd_directories.go

@@ -1,18 +1,20 @@
 package main
 
 import (
+	"bytes"
 	"fmt"
-	"os"
 	"text/tabwriter"
 
 	"github.com/cheat/cheat/internal/config"
+	"github.com/cheat/cheat/internal/display"
 )
 
 // cmdDirectories lists the configured cheatpaths.
 func cmdDirectories(opts map[string]interface{}, conf config.Config) {
 
 	// initialize a tabwriter to produce cleanly columnized output
-	w := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
+	var out bytes.Buffer
+	w := tabwriter.NewWriter(&out, 0, 0, 1, ' ', 0)
 
 	// generate sorted, columnized output
 	for _, path := range conf.Cheatpaths {
@@ -25,4 +27,5 @@ func cmdDirectories(opts map[string]interface{}, conf config.Config) {
 
 	// write columnized output to stdout
 	w.Flush()
+	display.Display(out.String(), conf)
 }

cmd/cheat/cmd_list.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 	"regexp"
@@ -9,6 +10,7 @@ import (
 	"text/tabwriter"
 
 	"github.com/cheat/cheat/internal/config"
+	"github.com/cheat/cheat/internal/display"
 	"github.com/cheat/cheat/internal/sheet"
 	"github.com/cheat/cheat/internal/sheets"
 )
@@ -85,10 +87,13 @@ func cmdList(opts map[string]interface{}, conf config.Config) {
 	}
 
 	// initialize a tabwriter to produce cleanly columnized output
-	w := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
+	var out bytes.Buffer
+	w := tabwriter.NewWriter(&out, 0, 0, 1, ' ', 0)
 
-	// generate sorted, columnized output
+	// write a header row
 	fmt.Fprintln(w, "title:\tfile:\ttags:")
+
+	// generate sorted, columnized output
 	for _, sheet := range flattened {
 		fmt.Fprintln(w, fmt.Sprintf(
 			"%s\t%s\t%s",
@@ -100,4 +105,5 @@ func cmdList(opts map[string]interface{}, conf config.Config) {
 
 	// write columnized output to stdout
 	w.Flush()
+	display.Display(out.String(), conf)
 }

cmd/cheat/cmd_search.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"github.com/cheat/cheat/internal/config"
+	"github.com/cheat/cheat/internal/display"
 	"github.com/cheat/cheat/internal/sheet"
 	"github.com/cheat/cheat/internal/sheets"
 )
@@ -87,12 +88,14 @@ func cmdSearch(opts map[string]interface{}, conf config.Config) {
 		}
 
 		// output the cheatsheet title
-		fmt.Printf("%s:\n", sheet.Title)
+		out := fmt.Sprintf("%s:\n", sheet.Title)
 
 		// indent each line of content with two spaces
 		for _, line := range strings.Split(sheet.Text, "\n") {
-			fmt.Printf("  %s\n", line)
+			out += fmt.Sprintf("  %s\n", line)
 		}
-		fmt.Println("")
+
+		// display the output
+		display.Display(out, conf)
 	}
 }

cmd/cheat/cmd_tags.go

@@ -5,6 +5,7 @@ import (
 	"os"
 
 	"github.com/cheat/cheat/internal/config"
+	"github.com/cheat/cheat/internal/display"
 	"github.com/cheat/cheat/internal/sheets"
 )
 
@@ -18,8 +19,12 @@ func cmdTags(opts map[string]interface{}, conf config.Config) {
 		os.Exit(1)
 	}
 
-	// write sheet tags to stdout
+	// assemble the output
+	out := ""
 	for _, tag := range sheets.Tags(cheatsheets) {
-		fmt.Println(tag)
+		out += fmt.Sprintln(tag)
 	}
+
+	// display the output
+	display.Display(out, conf)
 }

cmd/cheat/cmd_view.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"github.com/cheat/cheat/internal/config"
+	"github.com/cheat/cheat/internal/display"
 	"github.com/cheat/cheat/internal/sheets"
 )
 
@@ -47,5 +48,5 @@ func cmdView(opts map[string]interface{}, conf config.Config) {
 	}
 
 	// display the cheatsheet
-	fmt.Print(sheet.Text)
+	display.Display(sheet.Text, conf)
 }

configs/conf.yml

@@ -14,6 +14,9 @@ style: monokai
 # One of: "terminal", "terminal256", "terminal16m"
 formatter: terminal16m
 
+# Through which pager should output be piped? (Unset this key for no pager.)
+pager: less -FRX
+
 # The paths at which cheatsheets are available. Tags associated with a cheatpath
 # are automatically attached to all cheatsheets residing on that path.
 #

internal/config/config.go

@@ -5,6 +5,7 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 
 	cp "github.com/cheat/cheat/internal/cheatpath"
 
@@ -19,6 +20,7 @@ type Config struct {
 	Cheatpaths []cp.Cheatpath `yaml:"cheatpaths"`
 	Style      string         `yaml:"style"`
 	Formatter  string         `yaml:"formatter"`
+	Pager      string         `yaml:"pager"`
 }
 
 // New returns a new Config struct
@@ -111,5 +113,10 @@ func New(opts map[string]interface{}, confPath string, resolve bool) (Config, er
 		conf.Formatter = "terminal16m"
 	}
 
+	// if a pager was not provided, set a default
+	if strings.TrimSpace(conf.Pager) == "" {
+		conf.Pager = ""
+	}
+
 	return conf, nil
 }

internal/display/display.go

@@ -0,0 +1,37 @@
+package display
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+
+	"github.com/cheat/cheat/internal/config"
+)
+
+// Display writes output either directly to stdout, or through a pager,
+// depending upon configuration.
+func Display(out string, conf config.Config) {
+	// if no pager was configured, print the output to stdout and exit
+	if conf.Pager == "" {
+		fmt.Print(out)
+		os.Exit(0)
+	}
+
+	// otherwise, pipe output through the pager
+	parts := strings.Split(conf.Pager, " ")
+	pager := parts[0]
+	args := parts[1:]
+
+	// run the pager
+	cmd := exec.Command(pager, args...)
+	cmd.Stdin = strings.NewReader(out)
+	cmd.Stdout = os.Stdout
+
+	// handle errors
+	err := cmd.Run()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, fmt.Sprintf("failed to write to pager: %v", err))
+		os.Exit(1)
+	}
+}