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.
Live and let live.
Complete game on "FUBAR" difficulty.
Choose restraint.
Save a bullet.
Recover all Intel Items.
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.
Buck the chain of command.
Play it loose.
Kill 50 enemies with any sniper rifle. (campaign only)
Kill 10 enemies while they use zip lines or are rappelling. (campaign only)
Kill 50 enemies using only the Attack Command. (campaign only)
Live and let die.
Carry on, soldier.
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 vengeance.
Blow up 10 explosive objects, killing at least one enemy each time. (campaign only)
Kill 350 enemies with any rifle. (campaign only)
Kill 100 enemies with any pistol or SMG. (campaign only)
Kill 50 enemies with grenades. (campaign only)
Get out of here!
Kill 250 enemies with headshots. (campaign only)
Stand united.
Kill 75 enemies with any shotgun. (campaign only)
Show mercy.
Kill 150 enemies with any heavy weapon. (campaign only)
Recover 12 Intel Items.
Follow your orders.
Play it smart.
Stun an enemy by dumping sand on their head. (campaign only)
Face the horrors of war.
Kill an enemy by tagging him with a sticky grenade. (campaign only)
Kill an Edged Weapon Expert while he is up to 5 meters away. (campaign only)
Hit 10 enemies with your melee attack. (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)
Engineer an exit strategy.
Kill 3 enemies with a single grenade. (campaign only)
Sprint into cover 10 times while under fire. (campaign only)
We have contact.
Kill 5 enemies using blind fire. (campaign only)
Look out below.
Kill an enemy just as they are throwing a grenade. (campaign only)
What's lost is found.
Recover one Intel Item.
Kill an oryx. (campaign only)