Use sed to remove commented and blank lines

This is especially useful for config files. Say you have a file like:

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cats = True
# cats = False

cat_names = ["Plop","Fluffy"]
#

Let’s say your desired output is:

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cats = True
cat_names = ["Plop","Fluffy"]

If this awesome stuff if all in a file called cats.cfg, you would run a command like:

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sed  's/#.*$//;/^$/d'  cats.cfg

Add in -i to make the changes in line in cats.cfg.

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sed -i 's/#.*$//;/^$/d'  cats.cfg

Example

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$ cat cats.cfg
cats = True
# cats = False

cat_names = ["Plop","Fluffy"]
#
$ sed  's/#.*$//;/^$/d'  cats.cfg 
cats = True
cat_names = ["Plop","Fluffy"]
$