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Today I learned that I can use perl -c filename to find unmatched curly brackets {} in arbitrary files, not necessarily Perl scripts. The problem is, it doesn't work with other types of brackets () [] and maybe <>. I also had experiments with several Vim plugins that claims to help finding unmatched brackets but so far not so good.

I have a text file with quite a few brackets and one of them is missing! Is there any program / script / vim plugin / whatever that can help me identify the unmatched bracket?

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3 Answers 3

up vote 11 down vote accepted

In Vim you can use [ and ] to quickly travel to nearest unmatched bracket of the type entered in the next keystroke.

So [{ will take you back up to the nearest unmatched "{"; ]) would take you ahead to the nearest unmatched ")", and so on.

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Great, this is perfect for me. I'm about to accept this answer, but only waiting to see if there is a text processing tool that can analyze this. – phunehehe Mar 29 '11 at 11:05
I will also add that in vim you can use % (Shift 5, in the USA) to immediately find the matching bracket for the one you're on. – atroon Mar 29 '11 at 14:31
@atroon Ooo, nice. Didn't know that one yet myself. I love stackexchange sometimes. :) – Shadur Mar 30 '11 at 6:44
is <kbd>[</kbd> and <kbd>]</kbd> really jumping to the – wirrbel Aug 26 '13 at 14:54
I spent almost a day going through 4000 lines trying to find the missing } in R and this was the answer. Again, thank you VIM! But I think this is a good argument for splitting source code files into smaller chunks. – Thomas Browne Sep 3 '13 at 12:06

Update 2:
The following script now prints out the line number and column of a mismached bracket. It processes one bracket type per scan (ie. '[]' '<>' '{}' '()' ...)
The script identifies the first ,unmatched right bracket, or the first of any un-paired left bracket... On detecting an erroe, it exits with the line and column numbers

Here is some sample output...

File = /tmp/fred/test/
Pair = ()

*INFO:  Group 1 contains 1 matching pairs

ERROR: *END-OF-FILE* encountered after Bracket 7.
        A Left "(" is un-paired in Group 2.
        Group 2 has 1 un-paired Left "(".
        Group 2 begins at Bracket 3.
  see:  Line, Column (8, 10)
000008  (   )    (         (         (     )   )                    

Here is the script...


# Itentify the script
bname="$(basename "$0")"
# Make a work dir
[[ ! -d "$wdir" ]] && mkdir -p "$wdir"

# Arg1: The bracket pair 'string'
# pair='[]' # test
# pair='<>' # test
# pair='{}' # test
# pair='()' # test

# Arg2: The input file to test
  # Build a test source file
  cp /dev/null "$ifile"
  while IFS= read -r line ;do
    echo "$line" >> "$ifile"
  done <<EOF
[   ]    [         [         [
<   >    <         
                   <         >         
                             <    >    >         >
{   }    {         }         }         }         } 
(   )    (         (         (     )   )                    

echo "File = $ifile"
# Count how many: Left, Right, and Both
echo "Pair = $left$rght"
# Make a stripped-down 'skeleton' of the source file - brackets only
cp /dev/null "$skel"
# Make a String Of Brackets file ... (It is tricky manipulating bash strings with []..
sed 's/[^'${rght}${left}']//g' "$ifile" > "$skel"
< "$skel" tr  -d '\n'  > "$skel.str"
Left=($(<"$skel.str" tr -d "$left" |wc -m -l)); LeftCt=$((${Left[1]}-${Left[0]}))
Rght=($(<"$skel.str" tr -d "$rght" |wc -m -l)); RghtCt=$((${Rght[1]}-${Rght[0]}))
yBkts=($(sed -e "s/\(.\)/ \1 /g" "$skel.str"))

if (( eleCtB != BothCt )) ; then
  echo "ERROR:  array Item Count ($eleCtB)"
  echo "     should equal BothCt ($BothCt)"
  exit 1
  grpIx=0            # Keep track of Groups of nested pairs
  eleIxFir[$grpIx]=0 # Ix of First Bracket in a specific Group
  eleCtL=0           # Count of Left brackets in current Group 
  eleCtR=0           # Count of Right brackets in current Group
  errIx=-1           # Ix of an element in error.
  for (( eleIx=0; eleIx < eleCtB; eleIx++ )) ; do
    if [[ "${yBkts[eleIx]}" == "$left" ]] ; then
      # Left brackets are 'okay' until proven otherwise
      ((eleCtL++)) # increment Left bracket count
      ((eleCtR++)) # increment Right bracket count
      # Right brackets are 'okay' until their count exceeds that of Left brackets
      if (( eleCtR > eleCtL )) ; then
        echo "ERROR:  MIS-matching Right \"$rght\" in Group $((grpIx+1)) (at Bracket $((eleIx+1)) overall)"
      elif (( eleCtL == eleCtR )) ; then
        echo "*INFO:  Group $((grpIx+1)) contains $eleCtL matching pairs"
        # Reset the element counts, and note the first element Ix for the next group
  if (( eleCtL > eleCtR )) ; then
    # Left brackets are always potentially valid (until EOF)...
    # so, this 'error' is the last element in array
    echo "ERROR: *END-OF-FILE* encountered after Bracket $eleCtB."
    echo "        A Left \"$left\" is un-paired in Group $((grpIx+1))."
    echo "        Group $((grpIx+1)) has $unpairedCt un-paired Left \"$left\"."
    echo "        Group $((grpIx+1)) begins at Bracket $((eleIxFir[grpIx]+1))."

  # On error, get Line and Column numbers
  if (( errIx >= 0 )) ; then
    errLNum=0    # Source Line number (current).
    eleCtSoFar=0 # Count of bracket-elements in lines processed so far.
    errItemNum=$((errIx+1)) # error Ix + 1 (ie. "1 based")
    # Read the skeketon file to find the error line-number
    while IFS= read -r skline ; do
      brackets="${skline//[^"${rght}${left}"]/}" # remove whitespace
      if (( eleCtSoFar >= errItemNum )) ; then
        # We now have the error line-number
        # get the relevant Source Line 
        excerpt=$(< "$ifile" tail -n +$errLNum |head -n 1)
        # Homogenize the brackets (to be all "Left"), for easy counting
        mogX="${excerpt//$rght/$left}"; mogXCt=${#mogX} # How many 'Both' brackets on the error line? 
        if [[ "$errType" == "$left" ]] ; then
          # R-Trunc from the error element [inclusive]
          for (( ele=0; ele<eleTruncCt; ele++ )) ; do
            mogX="${mogX%"$left"*}"   # R-Trunc (Lazy)
          # errType=$rght
          mogX="${mogX%"$left"*}"   # R-Trunc (Lazy)
        echo "  see:  Line, Column ($errLNum, $errCNum)"
        echo "        ----+----1----+----2----+----3----+----4----+----5----+----6----+----7"  
        printf "%06d  $excerpt\n\n" $errLNum
    done < "$skel"
    echo "*INFO:  OK. All brackets are paired."
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This script is brilliant! – Jonathan Dumaine Jul 30 '13 at 21:31

The best option is vim/gvim as identified by Shadur, but if you want a script, you can check my answer to a similar question on Stack Overflow. I repeat my whole answer here:

If what you are trying to do applies to a general purpose language, then this is a non-trivial problem.

To start with you will have to worry about comments and strings. If you want to check this on a programming language that uses regular expressions, this will make your quest harder again.

So before I can come in and give you any advice on your question I need to know the limits of your problem area. If you can guarantee that there are no strings, no comments and no regular expressions to worry about - or more generically nowhere in the code that brackets can possibly be used other than for the uses for which you are checking that they are balanced - this will make life a lot simpler.

Knowing the language that you want to check would be helpful.

If I take the hypothesis that there is no noise, i.e. that all brackets are useful brackets, my strategy would be iterative:

I would simply look for and remove all inner bracket pairs: those that contain no brackets inside. This is best done by collapsing all lines to a single long line (and find a mechanism to to add line references, should you need to get that information out). In this case the search and replace is pretty simple:

It requires an array:

B["("]=")"; B["["]="]"; B["{"]="}"

And a loop through those elements:

for (b in B) {gsub("[" b "][^][(){}]*[" B[b] "]", "", $0)}

My test file is as follows:


($1 == "PID") {
  fo (i=1; i<NF; i++)
    F[$i] = i

($1 + 0) > 0 {

  pintf "VIRT=\t%12d\nRES=\t%12d\nSHR=\t%12d\n%%MEM=\t%5.1f%%\n", C["VIRT"], C["RES"], C["SHR"], C["%MEM"]

function count(c[)

  if ($f ~ /m$/)
    $f = ($f+0) * 1024


My full script (without line referencing) is as follows:

cat test-file-for-brackets.txt | \
  tr -d '\r\n' | \
  awk \
    BEGIN {
        for (b in B)
          m+=gsub("[" b "][^][(){}]*[" B[b] "]", "", $0)

The output of that script stops on the innermost illegal uses of brackets. But beware: 1/ this script will not work with brackets in comments, regular expressions or strings, 2/ it does not report where in the original file the problem is located, 3/ although it will remove all balanced pairs it stops at the innermost error conditions and keeps all englobbing brackets.

Point 3/ is probably an exploitable result, though I'm not sure of the reporting mechanism you had in mind.

Point 2/ is relatively easy to implement but takes more than a few minutes work to produce, so I'll leave it up to you to figure out.

Point 1/ is the tricky one because you enter a whole new realm of competing sometimes nested beginnings and endings, or special quoting rules for special characters...

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Thanks, you saved me. Had one mismatched brace in a 30k line json file. – I82Much Mar 20 '12 at 17:20

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