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