First, on the Linux command line, type: 

ciao4.5

Next, start idl, by typing:

idl

Each time you open IDL to do these emissivity look-ups, you'll issue the commands: 

atomdb = getenv('ATOMDB')

read_linelist,atomdb+'/apec_line.fits',line,t,n,l

Now, you're set to go; ready to look up, print, plot, etc. emissivities; here's 
epsilon = extract_line(line,8,8,1,4,temp,/actual_t)

Now, you can print out the retrieved values: 

print, epsilon

You can also print out the temperature grid: 

print, temp

And you can plot epsilon vs. temp:

cgplot,temp,epstot,/ylog,/xlog,xtit='Temperature (K)',ytit='!3Emissivity  (ph cm!u3!n s!u-1!n)',xr=[9.e5,1e8],xstyle=1,yr=[1.e-17,1.e-14],ystyle=1,charsize=1.5