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