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