matching a line with a literal asterisk "*" in grep

Question

Tried

$ echo "$STRING" | egrep "(\*)"

and also

$ echo "$STRING" | egrep '(\*)'

and countless other variations. I just want to match a line that contains a literal asterisk anywhere in the line.

Answer 1

Try a character class instead

echo "$STRING" | egrep '[*]'

Answer 2

Here's one way to match a literal asterisk:

$ echo "*" | grep "[*]"
*
$ echo "*" | egrep "[*]"
*
$ echo "asfd" | egrep "[*]"
$ echo "asfd" | grep "[*]"
$

Wrapping an expression in brackets usually allows you to capture a single special character easily; this will also work for a right bracket or a hyphen, for instance.

Be careful when this isn't in a bracket grouping:

$ echo "hi" | egrep "*"
hi
$ echo "hi" | grep "*"
$

Answer 3

Use:

grep "*" file.txt

or

cat file.txt | grep "*"