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