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