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