Bash Regex – How to Handle Multiple Matches in Bash Regular Expressions

bashregular expression

I have a nice little bash script which parses a message for a regular expression and does something with the capture groups:

regex='\((Closes|Resolves):\s([0-9]+)\)'
msg='Fixed a problem (Closes: 1234), (Resolves: 5678)'

if [[ $msg =~ $regex ]] ; then
  action="${BASH_REMATCH[1]}"
  issue="${BASH_REMATCH[2]}"
  do_something $action $issue
fi

This works well for the first match, but if there are multiple matches msg, later matches are ignored. Is there a way for me to loop through each match or is it time to start thinking of python or perl?

Best Answer

It's not explicitly supported by built-in bash syntax, but it can be easily achieved with a little variable substitution and some recursion.

function do_something {
  echo $1 $2
}

function handlematches {
  regex='\((Closes|Resolves):\s([0-9]+)\)'
  msg=$1

  if [[ $msg =~ $regex ]] ; then
    action="${BASH_REMATCH[1]}"
    issue="${BASH_REMATCH[2]}"
    do_something "$action" "$issue"

    # Remove the first regex match and try again
    handlematches "${msg/${BASH_REMATCH[0]}/}"
  fi
}

message='Fixed a problem (Closes: 1234), (Resolves: 5678)'
handlematches "$message"

Output:

Closes 1234
Resolves 5678

Related Solutions

Bash – Lazy regex using Bash

There is a reason why the internet is packed with alternative approaches. I can't really think of any situation where you would be forced to use bash for this. Why not use one of the tools designed for the job?

Anyway, as far as I know there is no way of doing non-greedy matches using the =~ operator. That's because it does not use bash's internal regex engine but your system's C one as defined in man 3 regex. This is explained in man bash:

   An additional binary operator, =~, is available, with the  same  prece‐
   dence  as  ==  and !=.  When it is used, the string to the right of the
   operator is considered  an  extended  regular  expression  and  matched
   accordingly  (as  in  regex(3)).

You can, however, do more or less what you want (bearing in mind that this is really not a good way of parsing HTML files) with a slightly different regex:

string='<span class="circle"> </span>foo</span></span>'
regex='<span class="circle"> </span>([^<]+)</span>'
[[ $string =~ $regex ]]; 
echo "${BASH_REMATCH[1]}"

The above will return foo as expected.

Bash – Seeing all regex matches in a file in Bash

Try grep -o 'myregex.*stuff' file and for the second question grep -o 'myregex.*stuff' file | sort | uniq.

The -o grep switch will print only the matches instead of printing the whole line that matches the regex.

Best Answer

Related Solutions

Bash – Lazy regex using Bash

Bash – Seeing all regex matches in a file in Bash

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