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