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.

Solution 1

Try a character class instead

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

Solution 2

echo "$STRING" | fgrep '*'

fgrep is used to match the special characters.

Solution 3

Simply escape the asterisk with a backslash:

grep "\*"

Solution 4

Use:

grep "*" file.txt

or

cat file.txt | grep "*"

Solution 5

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 "*"
$

View more solutions

Comments

[Daren Schwenke]

I usually just keep adding slashes until I get what I want. :)

[Gordon Davisson]

Both of your examples work for me (and also work with the parentheses removed).

[ghostdog74]

since you can do the first, the second one with cat is not necessary.

[DaveParillo]

I hear ya. Many people seem to like using cat to stream a file into all sorts of programs even though it's typically redundant. I just thought I'd include it to make the example look more familiar.

[DaveParillo]

Your example shows why I find this behavior of egrep irritating. If you want to do a literal string search with grep, just put it in quotes. Why would I ever want to grep for everything? unix calls that program 'cat' ;-) I hate the egrep forces you to bracket regex characters even if they are in double quotes. End of rant. Thanks!

[Gordon Davisson]

@DaveParillo: neither grep nor egrep know whether the pattern you passed them was quoted or not, as the quotes are interpreted by the shell before [e]grep is launched. The difference is due to how grep and egrep respond when the pattern starts with "", which is technically malformed ("" is a suffix). Try grep ".*" and you'll see that it matches everything. If you want a literal (non-regex) search, use fgrep instead.

[Brian Burns]

On Windows with GnuWin32, you can use grep [*] file.txt.

[tripleee]

... except if you have a file named literally * in the directory where you run that. The lesson (not particularly from this example, but generally) is to always quote your regular expressions, no matter how trivial.