pkg: /data/local/tmp/Superuser.apk Failure [INSTALL_FAILED_ALREADY_EXISTS] Cannot root samsung galaxy s4 GT-I9505. 

[*] Device found.
[*] Pushing exploit...
6970 KB/s (1283460 bytes in 0.179s)
[*] Pushing root tools...
7523 KB/s (366952 bytes in 0.047s)
7510 KB/s (1867568 bytes in 0.242s)
7475 KB/s (1578585 bytes in 0.206s)
    pkg: /data/local/tmp/Superuser.apk
Failure [INSTALL_FAILED_ALREADY_EXISTS]
[*] Rooting phone...
[+] This may take a few minutes.
[-] Failure.
[*] Cleaning up...
[*] Exploit complete. Press enter to reboot and exit.


I followed this guide. Motochopper downloaded from here.

Tried to delete file /data/local/tmp/Superuser.apk.

./adb.osx shell
shell@jflte:/ $ cd /data/local/tmp/
shell@jflte:/data/local/tmp $ ls -la


But there is no such file /data/local/tmp/Superuser.apk.

My os is os x. 

So my phone is not rooted. Checked by app root checker.

I tried to root several times. Reboot telephone but still fail.

Update

I removed app SuperUser from android device. Restart it. And tried to root again.

sh run.sh
[*]
[*] Motochopper: Android root exploit (Linux/OS X version)
[*] v1.1
[*] by Dan Rosenberg (@djrbliss)
[*]
[*] Tested on the Motorola Razr HD, Razr M, Razr Maxx HD, and Atrix HD.
[*] Supports lots of other devices as well. ;-)
[*]
[*] Before continuing, ensure that USB debugging is enabled and that
[*] your phone is connected via USB.
[*]
[*] WARNING: This will likely void the warranty on your device. I am
[*] not responsible for any damage to your phone as a result using this
[*] tool.
[*]
[*] Press enter to root your phone...

[*]
[*] Waiting for device...
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
[*] Device found.
[*] Pushing exploit...
6626 KB/s (1283460 bytes in 0.189s)
[*] Pushing root tools...
6926 KB/s (366952 bytes in 0.051s)
5723 KB/s (1867568 bytes in 0.318s)
5474 KB/s (1578585 bytes in 0.281s)
    pkg: /data/local/tmp/Superuser.apk
Success
[*] Rooting phone...
[+] This may take a few minutes.
[-] Failure.
[*] Cleaning up...
[*] Exploit complete. Press enter to reboot and exit.


Allthough error INSTALL_FAILED_ALREADY_EXISTS have gone, the telephone still not rooted. [-] Failure.
The problem isn't that a file already exists at that path: it's that the app you're trying to install is already installed on the phone. Have you previously tried to install SuperUser as a normal app? You need to uninstall it before you can root the phone. Uninstall it in the usual way from Settings → Apps.

In addition, the Motochopper exploit only works up to the 4.2.2 firmware for the Galaxy S4 (and only S4 variants with the Snapdragon chipset, not Exynos-based ones). If you've already updated to 4.3 or 4.4, this exploit can't work. You need to use another method, for example unlocking the bootloader the conventional way (though if the phone is carrier-branded the carrier probably has disabled unlocking the bootloader).