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