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