Shell Programming and Scripting

well, you would still need a loop to go through many such files. if its a while loop, such as

Code:

ls TOP* | while read F
do
 ....
done

then might as well pipe these files to sed (or awk) as its faster this way.

Are you sure? Each iteration of a loop with a pipe (if I got what you meant) means a new child process. 20000 files = 20000 processes. Lots of overhead.

With the shell-only version it does do things in a single process.

What IS regrettable (IMO) is that bash keeps changing - you can only do xx operation with version x.y and higher. While the same thing happens elsewhere: ksh vs maybe ksh93, newbies do not have a clue what bash version they have.

The OP uses bash so there is no need to loop or to use external commands (assuming no IFS characters in the filenames):

Code:

% ls TOP*
TOP_TABIN235_1_20090323.200903231830  TOP_TABIN240_20090323.200903231830
% files=(TOP*) files=(${files[@]%.*})
% printf '%s\n' "${files[@]##*_}"    
20090323
20090323

hi every body
i tried something may be add value in this discussion

tmp=TOP_TABIN240_20090323.200903231830
solve1=${tmp##*_} ; echo ${solve1%%.*}
20090323

yes, you are right, i am saying that.

I see that radoulov has given a pure bash solution, well , even so, there is not much of a difference in performance whether one do it in pure bash syntax or pipe to tools like awk.