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