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