Why does this match
[[ 'hithere' =~ hi* ]]
but this does not
[[ 'hithere' =~ *there ]]
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1Shouldn't it be '=~ . *there'?raina77ow– raina77ow2015-09-30 17:48:53 +00:00Commented Sep 30, 2015 at 17:48
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Yes, thank you! I imagined it was something simple.quickshiftin– quickshiftin2015-09-30 17:50:16 +00:00Commented Sep 30, 2015 at 17:50
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2 Answers
=~ is specifically a regular expressions operator. If you want to match zero or more characters, you'll need .* instead of just *.
[[ 'hithere' =~ hi.* ]] && echo "Yes"
Yes
[[ 'hithere' =~ .*there ]] && echo "Yes"
Yes
Without anchors, though, the match will succeed even without wildcards.
[[ 'hithere' =~ hi ]]
[[ 'hithere' =~ there ]]
# Add anchors to guarantee you're matching the whole phrase.
[[ 'hithere' =~ ^hi.*$ ]]
[[ 'hithere' =~ ^.*there$ ]]
For pattern matching, you can use = with an unquoted value. This uses bash pattern matching instead, which is what you were (evidently) expecting.
[[ 'hithere' = hi* ]] && echo "Yes"
Yes
[[ 'hithere' = *there ]] && echo "Yes"
Yes
3 Comments
quickshiftin
Thank you, this helps clarify perfectly. I was expecting to use bash pattern matching but instead using the regex operator.
chepner
Note that
[[ hithere =~ *there ]] has an exit status of 2 (not 1) to indicate that the regular expression was malformed, rather than a simple failure to match.quickshiftin
You have vicariously helped me add database filtering support to my little mysqldump wrapper, mysqlbkup, so thank you! Added support for both BASH pattern matching and POSIX Regex ;)
For basic regular expression
preceding * is just a character, not considered as special character of regex.
'*' is an ordinary character if it appears at the beginning of the RE
Source: http://man7.org/linux/man-pages/man7/regex.7.html
Answer by Jeff Bowman works because
[[ 'hithere' =~ .*there ]] && echo "Yes" there is a . before *.
