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