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 an enemy just as they are throwing a grenade. (campaign only)
Hit 10 enemies with your melee attack. (campaign only)
Follow your orders.
Live and let die.
Live and let live.
Carry on, soldier.
Complete game on "Walk on the Beach" difficulty.
You are relieved.
The end of the line.
Recover all Intel Items.
Kill 5 enemies using blind fire. (campaign only)
Kill 4 enemies with a shotgun in 10 seconds or less. (campaign only)
Kill 3 enemies with a single grenade. (campaign only)
Kill 50 enemies with any sniper rifle. (campaign only)
Kill 250 enemies with headshots. (campaign only)
Choose restraint.
Choose vengeance.
Get out of here!
Stand united.
Kill 10 enemies while they use zip lines or are rappelling. (campaign only)
Kill 150 enemies with any heavy weapon. (campaign only)
Save a bullet.
Show mercy.
Blow up 10 explosive objects, killing at least one enemy each time. (campaign only)
Kill 350 enemies with any rifle. (campaign only)
Buck the chain of command.
Play it loose.
Kill an enemy by tagging him with a sticky grenade. (campaign only)
Recover 12 Intel Items.
Stun an enemy by dumping sand on their head. (campaign only)
Kick an enemy by vaulting over a cover. (campaign only)
Face the horrors of war.
Kill an Edged Weapon Expert while he is up to 5 meters away. (campaign only)
Engineer an exit strategy.
We have contact.
Look out below.
Recover one Intel Item.
What's lost is found.
Kill an oryx. (campaign only)
Play it smart.
Complete game on "Combat Op" difficulty.
Complete game on "Suicide Mission" difficulty.
Kill 100 enemies with any pistol or SMG. (campaign only)
Kill 75 enemies with any shotgun. (campaign only)
Kill 50 enemies with grenades. (campaign only)
Sprint into cover 10 times while under fire. (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 50 enemies using only the Attack Command. (campaign only)
Complete game on "FUBAR" difficulty.