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