Here is the full list of all 50 Spec Ops: The Line achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Complete game on "FUBAR" difficulty.
Kill 50 enemies using only the Attack Command. (campaign only)
Kill 10 enemies while they use zip lines or are rappelling. (campaign only)
Recover all Intel Items.
Complete three chapters in a row without being killed or reloading a checkpoint.
Sprint into cover 10 times while under fire. (campaign only)
Complete any chapter with 60%+ accuracy without dying or reloading a checkpoint.
Kill an oryx. (campaign only)
Save a bullet.
Live and let die.
You are relieved.
Buck the chain of command.
Choose vengeance.
Play it loose.
Live and let live.
Complete game on "Walk on the Beach" difficulty.
Complete game on "Combat Op" difficulty.
Complete game on "Suicide Mission" difficulty.
Carry on, soldier.
The end of the line.
Kill 150 enemies with any heavy weapon. (campaign only)
Choose restraint.
Kill 5 enemies using blind fire. (campaign only)
Kill 100 enemies with any pistol or SMG. (campaign only)
Kill 50 enemies with grenades. (campaign only)
Get out of here!
Kill 4 enemies with a shotgun in 10 seconds or less. (campaign only)
Kill 75 enemies with any shotgun. (campaign only)
Stand united.
Hit 10 enemies with your melee attack. (campaign only)
Show mercy.
Blow up 10 explosive objects, killing at least one enemy each time. (campaign only)
Kill 350 enemies with any rifle. (campaign only)
Kill an Edged Weapon Expert while he is up to 5 meters away. (campaign only)
Kill 250 enemies with headshots. (campaign only)
Stun an enemy by dumping sand on their head. (campaign only)
Kill 50 enemies with any sniper rifle. (campaign only)
Kick an enemy by vaulting over a cover. (campaign only)
What's lost is found.
Look out below.
We have contact.
Engineer an exit strategy.
Face the horrors of war.
Play it smart.
Follow your orders.
Kill 3 enemies with a single grenade. (campaign only)
Recover one Intel Item.
Recover 12 Intel Items.
Kill an enemy by tagging him with a sticky grenade. (campaign only)
Kill an enemy just as they are throwing a grenade. (campaign only)