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