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