Ubuntu – Search for all files with a .sql extension in folders and sub folders

From man find

    -empty File is empty and is either a regular file or a directory.

So to find both empty files and directories it is sufficient to do

find ~/lists -empty

To indicate the type, you could use the %y output format specifier

          %y     File's type (like in ls -l), U=unknown type (shouldn't happen)

e.g.

find ~/lists -empty -printf '%y %p\n'

or make use of an external program like ls, which includes a --classify option

    -F, --classify
          append indicator (one of */=>@|) to entries

i.e.

find ~/lists -empty -exec ls -Fd {} \;

If your definition of 'empty' is expanded to include files containing only whitespace characters, then it becomes more complicated - and more computationally intensive, since now you need to actually open at least any non-empty files and examine their contents. The most efficient way I can think of off the top of my head would be something like

find ~/list \( -empty -o \( -type f -a ! -exec grep -qm1 '[^[:blank:]]' {} \; \) \) -exec ls -Fd {} \;

(either empty, OR a file AND grep does not detect at least one non-blank character). Likely there is a better way though.

TL;DR

Add -iname "*.log" after / to your find command. Refer to man page for more info

A more detailed answer

The task at hand is the following:

1. List files that match pattern *.log
2. Execute grep per each file to find whether or not it contains a specific string.
3. List the filename that has a match on the stdout

The example of how that can be accomplished can be seen bellow:

$ find /var/log -iname "*.log" -exec grep -l 'wlan' {} \+                      

Essentially there's 3 things at play:

• find does the job of finding files AND calling grep per list of filenames in the -exec ...{} \+ structure, where {} will be substituted with all the filenames found.
• -iname "*.log" can provide case-insensetive matching of the filenames
• -exec . . .{} \+ calls the low-level execve function that will spawn grep -l with the list of all the files found in front of it ( in the place of {} ).
• The \+ is the option that specifies for execve to pack as any files as possible in front of grep (the limit is set by ARG_MAX variable, is specific to exec, and for Ubuntu is at 2097152 as can be shown by getconf ARG_MAX command ). Once the limit is reached, exec will repeat the call to grep with more files packed as arguments. The \ is necessary to ensure + is interpreted as argument to find and not as another shell command.
• the -l option or grep shows files with matched string. -L would match files without the string.