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