Tries from Barry Daly, Iain Henderson and Jordan Coghlan, allied to 12 points from IRB Junior Player of the Year nominee JJ Hanrahan, steered Ireland past the Six Nations champions on a 27-12 scoreline.
Ruddock's charges will be bidding to make it two wins out of two against France in 2012, having beaten them in Grenoble in a hard-fought game during the Six Nations.
Ireland are guaranteed their best ever finish at an IRB Junior World Championship. If they win on Friday, they will claim fifth spot - a jump of three positions from last year's tournament.
Speaking ahead of the clash at Newlands Stadium, Ruddock said: "We are expecting another tough game against France, particularly as we defeated them in the Six Nations earlier in the year.
"They will be gunning for revenge. We have done our homework and hopefully our legs will carry us through another important victory."
The much-anticipated game will be shown live on TG4, and there will be a match report and reaction here on IrishRugby.ie afterwards.
IRELAND UNDER-20 Team & Replacements (v France Under-20s, IRB Junior World Championship 5th-6th Place Play-Off, Newlands Stadium, Cape Town, Friday, June 22, 2.15pm local time/1.15pm Irish time):
15. Peter Nelson (Dungannon/Ulster)
14. Barry Daly (UCD/Leinster)
13. Stuart Olding (Belfast Harlequins/Ulster)
12. Chris Farrell (Dungannon/Ulster)
11. Foster Horan (Lansdowne/Leinster)
10. JJ Hanrahan (UL Bohemians/Munster)
9. Kieran Marmion (Corinthians/Connacht)
1. Des Merrey (Clontarf/Leinster)
2. Niall Scannell (Dolphin/Munster) (capt)
3. Tadhg Furlong (Clontarf/Leinster)
4. Alan O'Connor (UCD/Leinster)
5. Tadhg Beirne (Lansdowne/Leinster)
6. Iain Henderson (Queen's University/Ulster)
7. Jordan Coghlan (UCD/Leinster)
8. Jack Conan (Old Belvedere/Leinster)
16. James Rael (Garryowen/Munster)
17. Peter Reilly (Lansdowne/Leinster)
18. Jake Cawley (Old Belvedere/Leinster)
19. Shane Buckley (Garryowen/Munster)
20. Aaron Conneely (Corinthians/Connacht)
21. Luke McGrath (UCD/Leinster)
22. Jack Carty (Buccaneers/Connacht)
23. Conor Finn (Buccaneers/Connacht)
2012 IRB JUNIOR WORLD CHAMPIONSHIP -
POOL B RESULTS:
Monday, June 4: England 64 Italy 5, University of Western Cape Stadium, Cape Town
Monday, June 4: South Africa 19 Ireland 23, Danie Craven Stadium, Stellenbosch
Friday, June 8: South Africa 52 Italy 3, University of Western Cape Stadium, Cape Town
Friday, June 8: England 20 Ireland 15, Danie Craven Stadium, Stellenbosch
Tuesday, June 12: Ireland 41 Italy 12, Cape Town Stadium, Cape Town
Tuesday, June 12: South Africa 28 England 15, Cape Town Stadium, Cape Town
5TH-8TH PLACE PLAY-OFFS -
Sunday, June 17: France 19 Australia 17, Newlands Stadium, Cape Town
Sunday, June 17: Ireland 27 England 12, University of Western Cape Stadium, Cape Town
5TH-6TH PLACE PLAY-OFF -
Friday, June 22: France v Ireland, Newlands Stadium, Cape Town, 2.15pm local time/1.15pm Irish time