Find certain starting and ending characters from a txt file.

Suppose I have a text file. There are right and left brackets([ and ]) in the text. I want to print all those lines that start with [ and end with ]. In my text file the number of [ and ] are not same which means there are some errors. I would also like to print the lines that starts with [ but does not end with ] and vice versa. Finally, I would also like to insert [ or ] where there were no brackets.

Answer 1

[Walter Roberson]

I generalized slightly to allow whitespace before the [ or after the ]

S = fileread('YourTextFileName.txt');
balanced = regexp(S, '^\s*\[.*\]\s*$', 'match', 'lineanchors', 'dotexceptnewline')
unbalancedleft = regexp(S, '^\s*\[.*[^\]\s]\s*$', 'match', 'lineanchors', 'dotexceptnewline')
unbalancedright = regexp(S, '^\s*[^\[\s].*\]\s*$', 'match', 'lineanchors', 'dotexceptnewline')

"Finally, I would also like to insert [ or ] where there were no brackets."

That is ambiguous as to whether you want to add in [ at the beginning of lines where it is not present but ] is present at the end of the line, or if instead you want to add in [ at the beginning of lines where the ] is not present at the end of the line -- that is does the "where there were no brackets" refer to the each end of the line, or does it refer to the case where neither [ nor ] was in place.

[am]

Actually I want to find a match from a cell array instead of a text file. I splitted each line of text into an cell array. I am trying to find the match from each array. The pattern i am trying to match is start with [ and ends with [. Basically it does not with ]. There can be multiple words between [ and [.

Why does this not work?

 myPattern = '\[[^\]]*';

[Cedric]

because you made a small mistake in the set of elements not to match, you should have

 myPattern = '\[[^\[]*';

according to what you just wrote above.

[Walter Roberson]

To find lines that begin with [ and end with [ with no possibility of leading or trailing spaces, then

   result = regexp(S, '^\[.*\[$', 'match', 'lineanchors', 'dotexceptnewline')

If you want to allow for possibly leading or trailing spaces then

   result = regexp(S, '^\s*\[.*\[\s*$', 'match', 'lineanchors', 'dotexceptnewline')

These expressions will work whether S is a string or a cell array. However, for a cell array you might get back empty entries corresponding to the places there was no match. For those,

mask = cellfun(@isempty, result);
result(mask) = [];