Looping with a read
Problem
What can you do with a while
loop? One common technique is to read the output of previous
commands. Let’s say you’re using the Subversion revision control system, which is executable
as svn. (This example is very similar
to what you would do for cvs as well.) When you check the status of a
directory subtree to see what files have been changed, you might see
something like this:
$ svn status bcb M bcb/amin.c ? bcb/dmin.c ? bcb/mdiv.tmp A bcb/optrn.c M bcb/optson.c ? bcb/prtbout.4161 ? bcb/rideaslist.odt ? bcb/x.maxc $
The lines that begin with question marks are files about which
Subversion has not been told; in this case they’re scratch files and
temporary copies of files. The lines that begin with an A
are newly added files, and those that begin
with M
have been modified since the
last changes were committed.
To clean up this directory it would be nice to get rid of all the scratch files, which are those files named in lines that begin with a question mark.
Solution
Try:
svn status mysrc | grep '^?' | cut -c8- | \ while read FN; do echo "$FN"; rm -rf "$FN"; done
or:
svn status mysrc | \ while read TAG FN do if [[ $TAG == \? ]] then echo $FN rm -rf "$FN" fi done
Discussion
Both scripts will do the same thing—remove files that svn reports with a question mark.
The first approach uses several subprograms to do its work (not a big deal in these days of gigahertz processors), and would fit on a single line in a typical terminal window. It uses grep to select only the ...
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