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