Re: Tutorial PSF subtraction

[Mohammad Akhlaghi]

Thanks Alex,

Indeed, this different behavior is very peculiar/strange! This is a very 
basic operation and they should behave similarly.

Just to see if this is an OS issue or a shell issue, can you try running 
the 'bash' command so you enter Bash (assuming it is present in your 
OS), then try setting 'imgs' and printing its value?

After that test, open a new terminal so you enter your default shell.

About the next problem, your guess is right: indeed, the shell has given 
the full string (including the new line characters!) to Arithmetic as a 
single token! This is again very strange and I hadn't seen this occur 
before!

These new-line characters were put in 'imgs' by 'ls'. But this is again 
non-standard! 'ls' usually prints all the names on a single line. For 
example on my computer (assuming I have two files called 'junk1.txt' and 
'junk2.txt'), I see this:

imgs=$(ls *.txt)
echo $imgs
junk1.txt junk2.txt

'ls' has an option '-1' (number one) for printing each file on a 
separate line. You can see the effect here:

imgs=$(ls -1 *.txt)
echo $imgs
junk1.txt
junk2.txt

Probably your 'ls' an alias to a customized 'ls' command that includes 
the '-1' option! You can check with this command:

alias | grep ls

If this is indeed the case, you can remove the alias for 'ls' with this 
command:

unalias ls

Then try setting 'imgs' and inspecting its value (to have all the files 
in one line).

If this is not the case, then things get more complicated, but I'll wait 
until you reply ;-).

Cheers,
Mohammad