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