Python3 script to backup all repos from gitlab. Just pipe the command output to a textfile (to run it later/somewhere else) or directly in your shell.

backup-all-repos-gitlab.py

from urllib.request import urlopen
import json
import subprocess, shlex
import sys

allProjects     = urlopen("http://gitlab.example.org/api/v3/projects/all?private_token=[PERSONAL_TOKEN]&per_page=100")
allProjectsDict = json.loads(allProjects.read().decode())
for index,thisProject in enumerate(allProjectsDict): 
    try:
        thisProjectURL = thisProject['ssh_url_to_repo'] + ' ' + thisProject['path_with_namespace'].replace('/', '_');
        sys.stdout.write('git clone ' + thisProjectURL)
        if index != (len(allProjectsDict) - 1):
            sys.stdout.write(' && ')

    except Exception as e:
        print("Error on %s: %s" % (thisProjectURL, e.strerror))