error in grep using a regex expression - regex

Question

I think I have uncovered an error in grep. If I run this grep statement against a db log on the command line it runs fine.
grep "Query Executed in [[:digit:]]\{5\}.\?" db.log
I get this result:
Query Executed in 19699.188 ms;"select distinct * from /xyztable.....
when I run it in a script
LONG_QUERY=`grep "Query Executed in [[:digit:]]\{5\}.\?" db.log`
the asterisk in the result is replaced with a list of all files in the current directory.
echo $LONG_QUERY
Result:
Query Executed in 19699.188 ms; "select distinct <list of files in
current directory> from /xyztable.....
Has anyone seen this behavior?

Answer 1

This is not an error in grep. This is an error in your understanding of how scripts are interpreted.
If I write in a script:
echo *
I will get a list of filenames, because an unquoted, unescaped, asterisk is interpreted by the shell (not grep, but /bin/bash or /bin/sh or whatever shell you use) as a request to substitute filenames matching the pattern '*', which is to say all of them.
If I write in a script:
echo "*"
I will get a single '*', because it was in a quoted string.
If I write:
STAR="*"
echo $STAR
I will get filenames again, because I quoted the star while assigning it to a variable, but then when I substituted the variable into the command it became unquoted.
If I write:
STAR="*"
echo "$STAR"
I will get a single star, because double-quotes allow variable interpolation.
You are using backquotes - that is, ` characters - around a command. That captures the output of the command into a variable.
I would suggest that if you are going to be echoing the results of the command, and little else, you should just redirect the results into a file. (After all, what are you going to do when your LONG_QUERY contains 10,000 lines of output because your log file got really full?)
Barring that, at the very least do echo "$LONG_QUERY" (in double quotes).