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