sharkdp · dan-hipschman · May 12, 2025
diff --git a/Cargo.toml b/Cargo.toml
@@ -9,7 +9,7 @@ readme = "README.md"
 repository = "https://github.com/sharkdp/hexyl"
 version = "0.16.0"
 edition = "2021"
-rust-version = "1.74"
+rust-version = "1.80"
 
 [dependencies]
 anyhow = "1.0"

diff --git a/README.md b/README.md
@@ -193,6 +193,21 @@ scoop install hexyl
 x env use hexyl
 ```
 
+## Configuration
+
+`hexyl` colors can be configured via environment variables. The variables used are as follows:
+
+ * `HEXYL_ASCII_PRINTABLE`: Any non-whitespace printable ASCII character
+ * `HEXYL_ASCII_WHITESPACE`: Whitespace such as space or newline (only visible in middle panel with byte values)
+ * `HEXYL_ASCII_OTHER`: Any other ASCII character (< `0x80`) besides null
+ * `HEXYL_NULL`: The null byte (`0x00`)
+ * `HEXYL_NONASCII`: Any non-ASCII byte (> `0x7F`)
+ * `HEXYL_OFFSET`: The lefthand file offset
+
+The colors can be any of the 8 standard terminal colors: `black`, `blue`, `cyan`, `green`, `magenta`, `red`,
+`yellow` and `white`. The "bright" variants are also supported (e.g., `bright blue`). Additionally, you can use
+the RGB hex format, `#abcdef`. For example, `HEXYL_ASCII_PRINTABLE=blue HEXYL_ASCII_WHITESPACE="bright green" HEXYL_ASCII_OTHER="#ff7f99"`.
+
 ## License
 
 Licensed under either of

diff --git a/doc/hexyl.1.md b/doc/hexyl.1.md
@@ -106,6 +106,21 @@ _FILE_
 **-V**, **\--version**
 :   Prints version information.
 
+# ENVIRONMENT VARIABLES
+
+**hexyl** colors can be configured via environment variables. The variables used are as follows:
+
+:   - **HEXYL_ASCII_PRINTABLE**: Any non-whitespace printable ASCII character
+    - **HEXYL_ASCII_WHITESPACE**: Whitespace such as space or newline (only visible in middle panel with byte values)
+    - **HEXYL_ASCII_OTHER**: Any other ASCII character (< **0x80**) besides null
+    - **HEXYL_NULL**: The null byte (**0x00**)
+    - **HEXYL_NONASCII**: Any non-ASCII byte (> **0x7F**)
+    - **HEXYL_OFFSET**: The lefthand file offset
+
+The colors can be any of the 8 standard terminal colors: **black**, **blue**, **cyan**, **green**, **magenta**, **red**,
+**yellow** and **white**. The "bright" variants are also supported (e.g., **bright blue**). Additionally, you can use
+the RGB hex format, **#abcdef**. For example, **HEXYL_ASCII_PRINTABLE=blue HEXYL_ASCII_WHITESPACE="bright green" HEXYL_ASCII_OTHER="#ff7f99"**.
+
 # NOTES
 
 Source repository:

diff --git a/src/colors.rs b/src/colors.rs
@@ -1,12 +1,39 @@
-use owo_colors::{colors, Color};
+use owo_colors::{colors, AnsiColors, Color, DynColors, OwoColorize};
+use std::str::FromStr;
+use std::sync::LazyLock;
 
-pub const COLOR_NULL: &[u8] = colors::BrightBlack::ANSI_FG.as_bytes();
-pub const COLOR_OFFSET: &[u8] = colors::BrightBlack::ANSI_FG.as_bytes();
-pub const COLOR_ASCII_PRINTABLE: &[u8] = colors::Cyan::ANSI_FG.as_bytes();
-pub const COLOR_ASCII_WHITESPACE: &[u8] = colors::Green::ANSI_FG.as_bytes();
-pub const COLOR_ASCII_OTHER: &[u8] = colors::Green::ANSI_FG.as_bytes();
-pub const COLOR_NONASCII: &[u8] = colors::Yellow::ANSI_FG.as_bytes();
-pub const COLOR_RESET: &[u8] = colors::Default::ANSI_FG.as_bytes();
+pub static COLOR_NULL: LazyLock<String> =
+    LazyLock::new(|| init_color("NULL", AnsiColors::BrightBlack));
+pub static COLOR_OFFSET: LazyLock<String> =
+    LazyLock::new(|| init_color("OFFSET", AnsiColors::BrightBlack));
+pub static COLOR_ASCII_PRINTABLE: LazyLock<String> =
+    LazyLock::new(|| init_color("ASCII_PRINTABLE", AnsiColors::Cyan));
+pub static COLOR_ASCII_WHITESPACE: LazyLock<String> =
+    LazyLock::new(|| init_color("ASCII_WHITESPACE", AnsiColors::Green));
+pub static COLOR_ASCII_OTHER: LazyLock<String> =
+    LazyLock::new(|| init_color("ASCII_OTHER", AnsiColors::Green));
+pub static COLOR_NONASCII: LazyLock<String> =
+    LazyLock::new(|| init_color("NONASCII", AnsiColors::Yellow));
+pub const COLOR_RESET: &str = colors::Default::ANSI_FG;
+
+fn init_color(name: &str, default_ansi: AnsiColors) -> String {
+    let default = DynColors::Ansi(default_ansi);
+    let env_var = format!("HEXYL_{}", name);
+    let color = match std::env::var(env_var).as_deref() {
+        Ok(color) => match DynColors::from_str(color) {
+            Ok(color) => color,
+            _ => default,
+        },
+        _ => default,
+    };
+    // owo_colors' API isn't designed to get the terminal codes directly for
+    // dynamic colors, so we use this hack to get them from the LHS of some text.
+    format!("{}", "|".color(color))
+        .split_once("|")
+        .unwrap()
+        .0
+        .to_owned()
+}
 
 #[rustfmt::skip]
 pub const CP437: [char; 256] = [

diff --git a/src/lib.rs b/src/lib.rs
@@ -84,11 +84,11 @@ impl Byte {
     fn color(self) -> &'static [u8] {
         use crate::ByteCategory::*;
         match self.category() {
-            Null => COLOR_NULL,
-            AsciiPrintable => COLOR_ASCII_PRINTABLE,
-            AsciiWhitespace => COLOR_ASCII_WHITESPACE,
-            AsciiOther => COLOR_ASCII_OTHER,
-            NonAscii => COLOR_NONASCII,
+            Null => COLOR_NULL.as_bytes(),
+            AsciiPrintable => COLOR_ASCII_PRINTABLE.as_bytes(),
+            AsciiWhitespace => COLOR_ASCII_WHITESPACE.as_bytes(),
+            AsciiOther => COLOR_ASCII_OTHER.as_bytes(),
+            NonAscii => COLOR_NONASCII.as_bytes(),
         }
     }
 
@@ -440,14 +440,14 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
                 .as_bytes(),
         )?;
         if self.show_color {
-            self.writer.write_all(COLOR_OFFSET)?;
+            self.writer.write_all(COLOR_OFFSET.as_bytes())?;
         }
         if self.show_position_panel {
             match self.squeezer {
                 Squeezer::Print => {
                     self.writer.write_all(b"*")?;
                     if self.show_color {
-                        self.writer.write_all(COLOR_RESET)?;
+                        self.writer.write_all(COLOR_RESET.as_bytes())?;
                     }
                     self.writer.write_all(b"       ")?;
                 }
@@ -462,7 +462,7 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
                             .write_all(self.byte_hex_panel_g[byte as usize].as_bytes())?;
                     }
                     if self.show_color {
-                        self.writer.write_all(COLOR_RESET)?;
+                        self.writer.write_all(COLOR_RESET.as_bytes())?;
                     }
                 }
             }
@@ -494,7 +494,7 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
         }
         if i == 8 * self.panels - 1 {
             if self.show_color {
-                self.writer.write_all(COLOR_RESET)?;
+                self.writer.write_all(COLOR_RESET.as_bytes())?;
                 self.curr_color = None;
             }
             self.writer.write_all(
@@ -505,7 +505,7 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
             )?;
         } else if i % 8 == 7 {
             if self.show_color {
-                self.writer.write_all(COLOR_RESET)?;
+                self.writer.write_all(COLOR_RESET.as_bytes())?;
                 self.curr_color = None;
             }
             self.writer.write_all(
@@ -531,12 +531,12 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
             Squeezer::Print => {
                 if !self.show_position_panel && i == 0 {
                     if self.show_color {
-                        self.writer.write_all(COLOR_OFFSET)?;
+                        self.writer.write_all(COLOR_OFFSET.as_bytes())?;
                     }
                     self.writer
                         .write_all(self.byte_char_panel[b'*' as usize].as_bytes())?;
                     if self.show_color {
-                        self.writer.write_all(COLOR_RESET)?;
+                        self.writer.write_all(COLOR_RESET.as_bytes())?;
                     }
                 } else if i % (self.group_size as usize) == 0 {
                     self.writer.write_all(b" ")?;
@@ -562,7 +562,7 @@ impl<'a, Writer: Write> Printer<'a, Writer> {
         if i % 8 == 7 {
             if self.show_color {
                 self.curr_color = None;
-                self.writer.write_all(COLOR_RESET)?;
+                self.writer.write_all(COLOR_RESET.as_bytes())?;
             }
             self.writer.write_all(b" ")?;
             // byte is last in last panel

diff --git a/src/main.rs b/src/main.rs
@@ -493,32 +493,32 @@ fn print_color_table() -> io::Result<()> {
     writeln!(stdout, "hexyl color reference:\n")?;
 
     // NULL bytes
-    stdout.write_all(COLOR_NULL)?;
+    stdout.write_all(COLOR_NULL.as_bytes())?;
     writeln!(stdout, "⋄ NULL bytes (0x00)")?;
-    stdout.write_all(COLOR_RESET)?;
+    stdout.write_all(COLOR_RESET.as_bytes())?;
 
     // ASCII printable
-    stdout.write_all(COLOR_ASCII_PRINTABLE)?;
+    stdout.write_all(COLOR_ASCII_PRINTABLE.as_bytes())?;
     writeln!(stdout, "a ASCII printable characters (0x20 - 0x7E)")?;
-    stdout.write_all(COLOR_RESET)?;
+    stdout.write_all(COLOR_RESET.as_bytes())?;
 
     // ASCII whitespace
-    stdout.write_all(COLOR_ASCII_WHITESPACE)?;
+    stdout.write_all(COLOR_ASCII_WHITESPACE.as_bytes())?;
     writeln!(stdout, "_ ASCII whitespace (0x09 - 0x0D, 0x20)")?;
-    stdout.write_all(COLOR_RESET)?;
+    stdout.write_all(COLOR_RESET.as_bytes())?;
 
     // ASCII other
-    stdout.write_all(COLOR_ASCII_OTHER)?;
+    stdout.write_all(COLOR_ASCII_OTHER.as_bytes())?;
     writeln!(
         stdout,
         "• ASCII control characters (except NULL and whitespace)"
     )?;
-    stdout.write_all(COLOR_RESET)?;
+    stdout.write_all(COLOR_RESET.as_bytes())?;
 
     // Non-ASCII
-    stdout.write_all(COLOR_NONASCII)?;
+    stdout.write_all(COLOR_NONASCII.as_bytes())?;
     writeln!(stdout, "× Non-ASCII bytes (0x80 - 0xFF)")?;
-    stdout.write_all(COLOR_RESET)?;
+    stdout.write_all(COLOR_RESET.as_bytes())?;
 
     Ok(())
 }