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