diff --git a/cli/src/config.rs b/cli/src/config.rs
index 42d06f14b..12d8b480f 100644
--- a/cli/src/config.rs
+++ b/cli/src/config.rs
@@ -22,6 +22,7 @@ use std::{env, fmt, slice};
 use config::Source;
 use itertools::Itertools;
 use jj_lib::settings::ConfigResultExt as _;
+use regex::{Captures, Regex};
 use thiserror::Error;
 use tracing::instrument;
 
@@ -661,12 +662,22 @@ impl CommandNameAndArgs {
 
     /// Returns process builder configured with this.
     pub fn to_command(&self) -> Command {
+        let empty: HashMap<&str, &str> = HashMap::new();
+        self.to_command_with_variables(&empty)
+    }
+
+    /// Returns process builder configured with this after interpolating
+    /// variables into the arguments.
+    pub fn to_command_with_variables<V: AsRef<str>>(
+        &self,
+        variables: &HashMap<&str, V>,
+    ) -> Command {
         let (name, args) = self.split_name_and_args();
         let mut cmd = Command::new(name.as_ref());
         if let CommandNameAndArgs::Structured { env, .. } = self {
             cmd.envs(env);
         }
-        cmd.args(args.as_ref());
+        cmd.args(interpolate_variables(&args, variables));
         cmd
     }
 }
@@ -693,6 +704,41 @@ impl fmt::Display for CommandNameAndArgs {
     }
 }
 
+// Not interested in $UPPER_CASE_VARIABLES
+static VARIABLE_REGEX: once_cell::sync::Lazy<Regex> =
+    once_cell::sync::Lazy::new(|| Regex::new(r"\$([a-z0-9_]+)\b").unwrap());
+
+pub fn interpolate_variables<V: AsRef<str>>(
+    args: &[String],
+    variables: &HashMap<&str, V>,
+) -> Vec<String> {
+    args.iter()
+        .map(|arg| {
+            VARIABLE_REGEX
+                .replace_all(arg, |caps: &Captures| {
+                    let name = &caps[1];
+                    if let Some(subst) = variables.get(name) {
+                        subst.as_ref().to_owned()
+                    } else {
+                        caps[0].to_owned()
+                    }
+                })
+                .into_owned()
+        })
+        .collect()
+}
+
+/// Return all variable names found in the args, without the dollar sign
+pub fn find_all_variables(args: &[String]) -> impl Iterator<Item = &str> {
+    let regex = &*VARIABLE_REGEX;
+    args.iter()
+        .flat_map(|arg| regex.find_iter(arg))
+        .map(|single_match| {
+            let s = single_match.as_str();
+            &s[1..]
+        })
+}
+
 /// Wrapper to reject an array without command name.
 // Based on https://github.com/serde-rs/serde/issues/939
 #[derive(Clone, Debug, Eq, Hash, PartialEq, serde::Deserialize)]
diff --git a/cli/src/merge_tools/external.rs b/cli/src/merge_tools/external.rs
index f8b3c70fb..1425a66d5 100644
--- a/cli/src/merge_tools/external.rs
+++ b/cli/src/merge_tools/external.rs
@@ -12,14 +12,13 @@ use jj_lib::merge::{Merge, MergedTreeValue};
 use jj_lib::merged_tree::{MergedTree, MergedTreeBuilder};
 use jj_lib::repo_path::RepoPath;
 use pollster::FutureExt;
-use regex::{Captures, Regex};
 use thiserror::Error;
 
 use super::diff_working_copies::{
     check_out_trees, new_utf8_temp_dir, set_readonly_recursively, DiffEditWorkingCopies, DiffSide,
 };
 use super::{ConflictResolveError, DiffEditError, DiffGenerateError};
-use crate::config::CommandNameAndArgs;
+use crate::config::{find_all_variables, interpolate_variables, CommandNameAndArgs};
 use crate::ui::Ui;
 
 /// Merge/diff tool loaded from the settings.
@@ -220,41 +219,6 @@ pub fn run_mergetool_external(
     Ok(new_tree)
 }
 
-// Not interested in $UPPER_CASE_VARIABLES
-static VARIABLE_REGEX: once_cell::sync::Lazy<Regex> =
-    once_cell::sync::Lazy::new(|| Regex::new(r"\$([a-z0-9_]+)\b").unwrap());
-
-fn interpolate_variables<V: AsRef<str>>(
-    args: &[String],
-    variables: &HashMap<&str, V>,
-) -> Vec<String> {
-    args.iter()
-        .map(|arg| {
-            VARIABLE_REGEX
-                .replace_all(arg, |caps: &Captures| {
-                    let name = &caps[1];
-                    if let Some(subst) = variables.get(name) {
-                        subst.as_ref().to_owned()
-                    } else {
-                        caps[0].to_owned()
-                    }
-                })
-                .into_owned()
-        })
-        .collect()
-}
-
-/// Return all variable names found in the args, without the dollar sign
-fn find_all_variables(args: &[String]) -> impl Iterator<Item = &str> {
-    let regex = &*VARIABLE_REGEX;
-    args.iter()
-        .flat_map(|arg| regex.find_iter(arg))
-        .map(|single_match| {
-            let s = single_match.as_str();
-            &s[1..]
-        })
-}
-
 pub fn edit_diff_external(
     editor: &ExternalMergeTool,
     left_tree: &MergedTree,