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