grep weird behaviour in linux command line

Question

I have a file test.txt which contains this text data

# cat test.txt
*@=>*@

if I use grep to check if the string is in the file using this way

# grep "*@=>*@" test.txt
#

it returns nothing..

while if I grep a partial string search

# grep "*@=>" test.txt
# *@=>*@

it works correctly ..

Why in the first case do grep return nothing ?

It is written in the manual (type `man grep` on your terminal): _"The grep utility searches any given input files, selecting lines that match one or more patterns. By default, a pattern matches an input line if the regular expression (RE) in the pattern matches the input line without its trailing newline."_ — axiac, Apr 08 '21 at 16:48

score 0 · Accepted Answer · answered Apr 08 '21 at 16:38

The asterisk is special to grep, it means "the previous token is repeated zero or more times". So >* would match an empty string or > or >> etc.

To match an asterisk, backslash it in the pattern:

grep '\*@=>\*@' test.txt

(The first asterisk follows no token, so the backslash is optional.)

grep weird behaviour in linux command line

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