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