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