[SOLVED] Some question when using regular expression , ask for help!
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[saturn@saturn-pc new]$ [[ "aab" =~ ab ]] && echo "ok" || echo "error";
[saturn@saturn-pc new]$ [[ "aab" =~ "ab" ]] && echo "ok" || echo "error";
"aab" should not match ab , Can you tell me why?
On the contrary, aab matches the regular expression ab, since it does contain the substring ab. If you want to match only the ab literal string, you have to insert word boundaries in the regular expression:
I thinks ab is only a fixed string, it does not contain any metacharacter such as . or * or ?, so I am very puzzled.
[saturn@saturn-pc new]$ [[ "aab" =~ ab ]] && echo "ok" || echo "error"
[saturn@saturn-pc new]$ [[ "aaaaab" =~ ab ]] && echo "ok" || echo "error"
ok !!ab seems has the same effect of a*b !!
[saturn@saturn-pc new]$ [[ "aaaaab" =~ a*b ]] && echo "ok" || echo "error"
[saturn@saturn-pc new]$ [[ "aabaab" =~ a*b ]] && echo "ok" || echo "error"
ok !!a*b means repeat "a" zero or more times, but it seems match any char one or more times !!
Regular expression is not the same as shell globbing..
Exactly correct, and it is not the same as string comparison. A regular expression tries to match any part of the string against which it is tested. The regex 'ab' will match any substring of 'aab', and since there is a substring 'ab', the test evaluates to 'True'.