diff --git a/include/exec.h b/include/exec.h
new file mode 100644
index 0000000..a761c3e
--- /dev/null
+++ b/include/exec.h
@@ -0,0 +1,6 @@
+#ifndef EXEC_H
+#define exec_h
+#include "types.h"
+
+struct line runextension(struct line *data, char *filename, size_t n);
+#endif
diff --git a/src/lib/exec.c b/src/lib/exec.c
new file mode 100644
index 0000000..eb0aebc
--- /dev/null
+++ b/src/lib/exec.c
@@ -0,0 +1,73 @@
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "arg.h"
+#include "types.h"
+#include "util.h"
+
+struct line runextension(struct line *data, char *filename, size_t n) {
+  struct line line;
+
+  int in[2];
+  int out[2];
+  if (pipe(out) == -1 || pipe(in) == -1)
+    die("pipe");
+
+  pid_t pid = fork();
+  if (pid == -1)
+    die("fork");
+
+  if (pid == 0) {
+    // child
+    dup2(out[1], STDOUT_FILENO);
+    close(out[0]);
+    close(out[1]);
+
+    dup2(in[1], STDIN_FILENO);
+    close(in[0]);
+    close(in[1]);
+
+    char *eargv[4];
+    eargv[0] = conf.extension;
+    eargv[1] = filename;
+    eargv[2] = malloc((intlen(n) + 1) * sizeof(char));
+    if (eargv[2] == NULL)
+      die("malloc");
+    sprintf(eargv[2], "%zu", n);
+    eargv[3] = NULL;
+
+    if (execvp(conf.extension, eargv) == -1)
+      die("exec");
+  } else {
+    // parent
+    close(out[1]);
+    close(in[1]);
+
+    write(in[0], "test\0", 4);
+
+    char *buf = malloc(256);
+    memset(buf, '\0', 256);
+
+    size_t len = read(out[0], buf, 256);
+
+    line.buf = buf;
+    line.len = len;
+
+    int status;
+    waitpid(pid, &status, 0);
+
+    if (WEXITSTATUS(status) != EXIT_SUCCESS) {
+      die("exec fail");
+    }
+  }
+
+  close(out[0]);
+  close(out[1]);
+  close(in[0]);
+  close(in[1]);
+
+  return line;
+}
diff --git a/src/main.c b/src/main.c
index 781ab41..66cedbd 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,11 +1,13 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
 #include "arg.h"
+#include "exec.h"
 #include "file.h"
 #include "process.h"
 #include "types.h"
 #include "util.h"
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
 
 #define INVERT_T "\x1b[7m"
 #define UINVERT_T "\x1b[27m"
@@ -89,6 +91,7 @@ void run(FILE *fp, char *filename, bool tty) {
           free(padding);
         }
 
+        f.lines[i] = runextension(&f.lines[i], filename, i + 1);
         fwrite(f.lines[i].buf, 1, f.lines[i].len, st);
         fprintf(st, "\n");
         linecount++;