Suppress Coloring via Environment Variables
On several occasions I have stumbled on to different ways to suppress coloring in the terminal.
Two competing ways to handle coloring in the terminal is to use the NO_COLOR environment variable or the CLICOLOR and associated environment variables.
The two however have different approaches to the problem.
Where NO_COLOR can be set to suppress color output, CLICOLOR can be set to force color output and disable color output.
Our Contestants
NO_COLOR
If $NO_COLOR is set, then the output should not contain any color.
Command line flags and configuration parameters that are intended to control color output this should override $NO_COLOR.
This is the approach described on the NO_COLOR website.
To support this in Go, the following code can be used:
package main
import (
"fmt"
"os"
)
func main() {
_, ok := os.LookupEnv("NO_COLOR")
if ok {
fmt.Println("NO_COLOR is set")
} else {
fmt.Println("NO_COLOR is not set")
}
}
In Go if a environment variable is not set, then os.Getenv() returns an empty string, so we need to use: os.LookupEnv().
Compared to the $CLICOLOR approach, this is a very basic approach. And the NO_COLOR approach does not specify handling of the value of the environment variable, just it’s presence.
CLICOLOR
If $CLI_COLOR is different from 0, then the output be colorized, if supported by the application and the terminal.
If the input is piped, then the output should not contain color.
If $CLI_COLOR is set to 0, then the output should not contain color.
If $CLI_COLOR_FORCE is different from 0, then the output should contain color, , if supported by the application and the terminal.
This is the approach taken by the CLICOLOR website. The website does not specify command line flags and configuration parameters that are intended to control color.
It does however specify that the $CLICOLOR_FORCE environment variable should override $CLICOLOR and piped output, should not be colorized.
package main
import (
"fmt"
"os"
)
func main() {
clicolor := os.Getenv("CLICOLOR")
clicolor_force := os.Getenv("CLICOLOR_FORCE")
// REF: https://stackoverflow.com/questions/43947363/detect-if-a-command-is-piped-or-not
fi, _ := os.Stdin.Stat()
if fi.Mode()&os.ModeCharDevice == 0 {
fmt.Println("STDIN is not a terminal")
} else {
fmt.Println("STDIN is a terminal")
}
if clicolor == "0" || clicolor == "" {
fmt.Println("CLICOLOR is not set")
if clicolor_force == "0" || clicolor_force == "" {
fmt.Println("CLICOLOR_FORCE is not set")
} else {
fmt.Println("CLICOLOR_FORCE is set")
}
} else {
fmt.Println("CLICOLOR is set")
}
}
Combining the Two
Based on the above, we can combine the two approaches, even though they differ in perspective.
package main
import (
"fmt"
"os"
)
func main() {
if color() {
fmt.Println("Color is enabled")
} else {
fmt.Println("Color is disabled")
}
}
func color() bool {
if nocolor() {
return false
} else if clicolor() {
return true
} else {
return false
}
}
func nocolor() bool {
_, ok := os.LookupEnv("NO_COLOR")
if ok {
fmt.Println("NO_COLOR is defined")
return true
} else {
fmt.Println("NO_COLOR is not defined")
return false
}
}
func clicolor() bool {
clicolor := os.Getenv("CLICOLOR")
clicolor_force := os.Getenv("CLICOLOR_FORCE")
// REF: https://stackoverflow.com/questions/43947363/detect-if-a-command-is-piped-or-not
fi, _ := os.Stdin.Stat()
if fi.Mode()&os.ModeCharDevice == 0 {
fmt.Println("STDIN is from a pipe")
return false
} else {
fmt.Println("STDIN is a terminal")
}
if clicolor == "0" || clicolor == "" {
fmt.Println("CLICOLOR is not set")
if clicolor_force == "0" || clicolor_force == "" {
fmt.Println("CLICOLOR_FORCE is not set")
return false
} else {
fmt.Println("CLICOLOR_FORCE is set")
return true
}
} else {
fmt.Println("CLICOLOR is set")
return true
}
}