The beard is alowed until it does not reduce effectiveness of special equipment (gaze mask, googles,..). It need to be clean.
Some exemptions :
Special forces could wearing beards if it's useful for the mission (infiltrate, disguise)
In Muslim's (like Afghanistan)country the beard could be used for better relationship with local people.
For the Legion Pioneers of the traditional section (1st REG) it's official since 1844. During assault against defended walls or entrenchment, the death chances was so high that they was alowed to be unshaved prior the assault and could keep the beard as an "combat proven" man.
Short beard = rooky
Long beard = killing machine (or lucky one

)
http://upload.wikimedia.org/wikipedi...ier-legion.JPG
In the modern time this section this used, for the Bastille Day, as an honor escort squad for a high valued or bellowed NCO of the FFL. It's alow him to open the way for the Legion troops.
http://upload.wikimedia.org/wikipedi...s-Camerone.jpg