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.
Complete game on "FUBAR" difficulty.
Kill 10 enemies while they use zip lines or are rappelling. (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.
Hit 10 enemies with your melee attack. (campaign only)
Kill 75 enemies with any shotgun. (campaign only)
Kill 4 enemies with a shotgun in 10 seconds or less. (campaign only)
Kill 50 enemies with grenades. (campaign only)
Choose restraint.
Play it smart.
Kill 150 enemies with any heavy weapon. (campaign only)
You are relieved.
Buck the chain of command.
Save a bullet.
Kill an oryx. (campaign only)
Live and let live.
Live and let die.
The end of the line.
Complete game on "Walk on the Beach" difficulty.
Complete game on "Combat Op" difficulty.
Carry on, soldier.
Recover all Intel Items.
Choose vengeance.
Get out of here!
Kill an enemy by tagging him with a sticky grenade. (campaign only)
Kill 250 enemies with headshots. (campaign only)
Blow up 10 explosive objects, killing at least one enemy each time. (campaign only)
Stand united.
Kick an enemy by vaulting over a cover. (campaign only)
Show mercy.
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 with any sniper rifle. (campaign only)
Kill 350 enemies with any rifle. (campaign only)
Follow your orders.
Play it loose.
Recover 12 Intel Items.
Kill 50 enemies using only the Attack Command. (campaign only)
Sprint into cover 10 times while under fire. (campaign only)
Face the horrors of war.
Kill 3 enemies with a single grenade. (campaign only)
Kill 5 enemies using blind fire. (campaign only)
Kill 100 enemies with any pistol or SMG. (campaign only)
Engineer an exit strategy.
We have contact.
Kill an enemy just as they are throwing a grenade. (campaign only)
Look out below.
Recover one Intel Item.
What's lost is found.