diff --git a/string_builder.c b/string_builder.c
index ddb6aad..267bb6e 100644
--- a/string_builder.c
+++ b/string_builder.c
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <ctype.h>
 
 #include "string_builder.h"
 
@@ -72,3 +73,27 @@ StringBuilder_write(StringBuilder *sb, const char *s)
         StringBuilder_write_char(sb, s[i]);
     }
 }
+
+void
+StringBuilder_trim(StringBuilder *sb)
+{
+    int start, end;
+    for (start = 0; start < sb->size; start++) {
+        if (!isspace(sb->s[start])) {
+            break;
+        }
+    }
+    for (end = sb->size-2; end > start; end--) {
+        if (!isspace(sb->s[end])) {
+            break;
+        }
+    }
+    int size = end - start + 1;
+    char *s = StringBuilder_malloc(size);
+    strncpy(s, sb->s + start, size);
+    s[size] = '\0';
+    free(sb->s);
+    sb->s = s;
+    sb->cap = size;
+    sb->size = size;
+}
diff --git a/string_builder.h b/string_builder.h
index d06bf1f..6b4e682 100644
--- a/string_builder.h
+++ b/string_builder.h
@@ -14,6 +14,7 @@ void StringBuilder_free(StringBuilder *sb);
 char * StringBuilder_str(StringBuilder *sb);
 void StringBuilder_write_char(StringBuilder *sb, char c);
 void StringBuilder_write(StringBuilder *sb, const char *s);
+void StringBuilder_trim(StringBuilder *sb);
 
 #endif /* STRING_BUILDER_H */
 
diff --git a/ttygif.c b/ttygif.c
index c62c56f..c931510 100644
--- a/ttygif.c
+++ b/ttygif.c
@@ -159,7 +159,7 @@ take_snapshot_darwin(const char *img_path, Options o)
 int
 take_snapshot_linux(const char *img_path, Options o)
 {
-    static char cmd [256];
+    static char cmd [1024];
 
     // ensure text has been written before taking screenshot
     usleep(50000);
@@ -317,23 +317,10 @@ main (int argc, char **argv)
 
 #ifdef OS_DARWIN
     options.img_ext = "png";
-    const char *terminal_app = getenv("TERM_PROGRAM");
-    if (terminal_app == NULL || !strlen(terminal_app)) {
-        fatalf("Error: TERM_PROGRAM environment variable was empty.");
-    }
-    if (strcmp(terminal_app, "Apple_Terminal") == 0) {
-        terminal_app = "Terminal.app";
-    }
-    int window_id = osx_get_window_id(terminal_app);
-    char window_id_buffer[256];
-    sprintf(window_id_buffer, "%d", window_id);
-    options.window_id = window_id_buffer;
+    options.window_id = osx_get_window_id();
 #else
     options.img_ext = "xwd";
-    options.window_id = getenv("WINDOWID");
-    if (options.window_id == NULL || !strlen(options.window_id)) {
-        fatalf("Error: WINDOWID environment variable was empty.");
-    }
+    options.window_id = linux_get_window_id();
 #endif
 
     if (options.debug) {
diff --git a/utils.c b/utils.c
index ce2f150..63a279c 100644
--- a/utils.c
+++ b/utils.c
@@ -1,6 +1,7 @@
 #include <stdio.h>
 #include <stdarg.h>
 #include <stdlib.h>
+#include <string.h>
 #include "string_builder.h"
 
 void fatalf(const char *format, ...)
@@ -12,28 +13,58 @@ void fatalf(const char *format, ...)
     exit(EXIT_FAILURE);
 }
 
-int osx_get_window_id(const char *app_name)
+int exec_command(StringBuilder *sb, const char *command)
 {
-    char command[1024];
-    sprintf(command,
-            "osascript -so -e 'tell app \"%s\" to id of window 1' 2> /dev/null",
-            app_name);
-
     FILE *fp = popen(command, "r");
     if (fp == NULL) {
-        fatalf("Error: failed to run command: %s", command);
+        return -1;
     }
-
-    int window_id;
-    if (fscanf(fp, "%d", &window_id) != 1) {
-        fatalf("Error: failed to parse window id: %s", command);
+    char buffer[1024];
+    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
+        StringBuilder_write(sb, buffer);
     }
+    return pclose(fp);
+}
 
-    pclose(fp);
+char * osx_get_window_id()
+{
+    const char *term = getenv("TERM_PROGRAM");
+    if (term == NULL || !strlen(term)) {
+        fatalf("Error: TERM_PROGRAM environment variable was empty.");
+    }
+    if (strcmp(term, "Apple_Terminal") == 0) {
+        term = "Terminal.app";
+    }
+    char command[1024];
+    sprintf(command,
+            "osascript -so -e 'tell app \"%s\" to id of window 1' 2> /dev/null",
+            term);
+    StringBuilder *sb = StringBuilder_new();
+    int code = exec_command(sb, command);
+    if (code != 0) {
+        fatalf("failed to run command: %s", command);
+    }
+    StringBuilder_trim(sb);
+    return StringBuilder_str(sb);
+}
 
-    return window_id;
+char * linux_get_window_id()
+{
+    StringBuilder *sb = StringBuilder_new();
+    const char *window_id = getenv("WINDOWID");
+    if (window_id != NULL && strlen(window_id)) {
+        StringBuilder_write(sb, window_id);
+        return StringBuilder_str(sb);
+    }
+    int code = exec_command(sb, "xdotool getwindowfocus");
+    if (code != 0) {
+        fatalf("Error: WINDOWID environment variable was empty.");
+    }
+    StringBuilder_trim(sb);
+    return StringBuilder_str(sb);
 }
 
+
 int exec_with_output(const char *command)
 {
     FILE *fp = popen(command, "r");
diff --git a/utils.h b/utils.h
index 7a03b7b..2390bc6 100644
--- a/utils.h
+++ b/utils.h
@@ -3,7 +3,8 @@
 #define _UTILS_H
 
 void fatalf(const char *format, ...);
-int osx_get_window_id(const char *app_name);
+char * osx_get_window_id();
+char * linux_get_window_id();
 int exec_with_output(const char *command);
 
 #endif /* _UTILS_H */