Matching string that contains asterisk [duplicate] - php

Question

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Reference - What does this regex mean?
(1 answer)
Regular expressions: Ensuring b doesn't come between a and c
(4 answers)
Closed 3 years ago.
I know this sounds easy but I am stuck.
I want to match strings that has asterisk *.
Essentially I want to allow strings having asterisk at front/back/both but not middle:
(At max there will be 2 asterisks, front and both but no middle, and the presence string is a must)
ALLOW:
*string* *string string* string
DENY:
*str*ing*
*str*ing str*ing* str*ing
*string*****
I tried
^\\*?((?!\\*).)*\\\*?$
and somehow it works.
Can someone explains how this works?
And verify if this is correct because regex..hard to debug and check..

Answer 1

You can use the following regex:
^\*?\w+\*?$
demo: https://regex101.com/r/vwuXv2/1/
Explanations:
^ anchor imposing the start of a line
\*? a * appearing at most one time
\w+ at least 1 word char appearing in the text ([a-zA-Z0-9_] feel free to change it depending on your need)
\*? a * appearing at most one time
$ end of line anchor
Now if you are interested in partial line matches, you can use the following regex:
(?<=^| )\*?\w+\*?(?=$| )
demo: https://regex101.com/r/vwuXv2/2/
Explanations: you add lookbehind, lookahead assertions.
Adding Japanese characters as requested in the comment (add in [^*\s] all the characters you need to exclude from the words):
^\*?[^*\s]+\*?$
demo: https://regex101.com/r/RaCmwt/1/
or
^\*?[[:alpha:]]+\*?$
(with unicode flag enabled) or just
^\*?\p{L}+\*?$
demo: https://regex101.com/r/RaCmwt/2/

Answer 2

You can simply say: Optionally start with asterisk, 0 or more arbitrary characters except asterisk, optionally end with asterisk.
^\*?[^*]*\*?$
https://regex101.com/r/bibCEc/2
An alternative is to inverse the match and test if there is not ( i.e. if(!...)) any asterisk not at the begin or end using negative look behind and look ahead:
(?<!^)\*(?!$)
https://regex101.com/r/8St0M4/2
According to your recent edit you would use the quatifier + to match 1 or more characters:
^\*?[^*]+\*?$
https://regex101.com/r/bibCEc/3