Bash if statement with regex

Question

I try to use REGEX in bash in order to check if the parameter seems to be a valid path following this format:

/first/second

In java I use with success the following REGEX :

((\\/)[a-zA-Z0-9\\s_@\\-!#$%&+=]+)+

But in bash I have some issue that I can't explain. In order to simplify my comprehension I try to use a simpler REGEX like that:

CHECKPATH="!/first/second"
REGEX_PATH="((\/)[a-zA-Z0-9]+)+"
if [[ ! ${CHECKPATH} =~ $REGEX_PATH ]]; then
    echo "error"
else
    echo "OK"
fi

I insert an "!" in the path just to check. So I should have "error" but not. With or without the "!" it changes nothing, what's the problem?

Update: (moved author's subquestion here from a comment)

One more thing, if I use ^((\/)[a-zA-Z0-9\s_@#&%!$+=\-]+)+$ it's ok, but it's not with ^((\/)[a-zA-Z0-9\s_@\-#&%!$+=]+)+$. I just changed the position of "\-" inside the regex, why?

you might need to add ^ and $ for begins with and ends with. try testing it here: regexpal.com — Buzz
– Buzz, Commented Nov 2, 2016 at 16:17
Works for me in bash 3.2 and and 4.3, with or with the ! in the value of CHECKPATH. — chepner
– chepner, Commented Nov 2, 2016 at 16:20

Peter Uhnak · Accepted Answer · 2016-11-02 20:45:56Z

2

Some regex libraries (possible the Java one you use) have methods that specifically test the regex against the whole input string.

But in bash (and generally in regex) you use:

^ - match start of the input, and
$ - match end of the input

So instead try,

REGEX_PATH="^((\/)[a-zA-Z0-9]+)+$"

Update:

You have to put the dash on the start/end.

http://man7.org/linux/man-pages/man7/regex.7.html :

To include a literal '-', make it the first or last character, or the second endpoint of a range. To use a literal '-' as the first endpoint of a range, enclose it in "[." and ".]" to make it a collating element (see below).

AND (same link) [emphasis mine]

With the exception of these and some combinations using '[' (see next paragraphs), all other special characters, including '\', lose their special significance within a bracket expression.

edited Nov 2, 2016 at 20:45

answered Nov 2, 2016 at 16:17

Peter Uhnak

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2 Comments

gduh Over a year ago

One more thing, if I use ^((\/)[a-zA-Z0-9\s_@#&%!$+=\-]+)+$ it's ok, but it's not with ^((\/)[a-zA-Z0-9\s_@\-#&%!$+=]+)+$. I just change the position of "\-" inside the regex, why ?

Peter Uhnak Over a year ago

@gduh I've moved this subquestion to the original question and added update to my answer.

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