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