1 files changed, 58 insertions, 0 deletions
diff --git a/envflag/main.go b/envflag/main.go
new file mode 100644
index 0000000..09c1f97
--- /dev/null
+++ b/envflag/main.go
@@ -0,0 +1,58 @@
+package envflag
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"strconv"
+)
+
+// String is a convent way to set value from environment variable,
+// and allow override when a command line flag is set. It's assumed `p` is
+// not nil.
+func String(fl *flag.FlagSet, p *string, name, envvar, usage string) {
+	if v := os.Getenv(envvar); v != "" {
+		*p = v
+	}
+
+	fl.StringVar(p, name, *p, fmt.Sprintf("%s (Environ: '%s')", usage, envvar))
+}
+
+// Bool is a convent way to set value from environment variable,
+// and allow override when a command line flag is set. It's assumed `p` is
+// not nil.
+func Bool(fl *flag.FlagSet, p *bool, name, envvar, usage string) error {
+	if v := os.Getenv(envvar); v != "" {
+		res, err := strconv.ParseBool(v)
+
+		if err != nil {
+			return fmt.Errorf("Bool: cannot parse '%s=%s', %w",
+				envvar, v, err)
+		}
+
+		*p = res
+	}
+
+	fl.BoolVar(p, name, *p, fmt.Sprintf("%s (Environ: '%s')", usage, envvar))
+
+	return nil
+}
+
+// Int is a convent way to set value from environment variable,
+// and allow override when a command line flag is set. It's assumed `p` is
+// not nil.
+func Int(fl *flag.FlagSet, p *int, name, envvar, usage string) error {
+	if v := os.Getenv(envvar); v != "" {
+		res, err := strconv.ParseInt(v, 10, 32)
+		if err != nil {
+			return fmt.Errorf("Int: cannot parse '%s=%s', %w",
+				envvar, v, err)
+		}
+
+		*p = int(res)
+	}
+
+	fl.IntVar(p, name, *p, fmt.Sprintf("%s (Environ: '%s')", usage, envvar))
+
+	return nil
+}