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