45.18.1 Introduction to basename and dirname

The basename command strips any "path" name components from a filename, leaving you with a "pure" filename. For example:

% basename /usr/bin/gigiplot
gigiplot
% basename /home/mikel/bin/bvurns.sh
bvurns.sh

basename can also strip a suffix from a filename. For example:

% basename /home/mikel/bin/bvurns.sh .sh
bvurns

The dirname command strips the filename itself, giving you the "directory" part of the pathname:

% dirname /usr/bin/screenblank
/usr/bin
% dirname local
.

If you give dirname a "pure" filename (i.e., a filename with no path, as in the second example), it tells you that the directory is . (the current directory).

NOTE: dirname and basename have a bug in many System V implementations. They don't recognize the second argument as a filename suffix to strip. Here's a good test:

% basename 0.foo .foo

If the answer is 0, your basename implementation is good. If the answer is 0.foo, the implementation is bad. If basename doesn't work, dirname won't, either.

45.18.2 Use with Loops

Here's an example of basename and dirname. There's a directory tree with some very large files - over 100,000 characters. You want to find those files, run split (35.9) on them, and add huge. to the start of the original filename. By default, split names the file chunks xaa, xab, xac, and so on; you want to use the original filename and a dot (.) instead of x:

|| exit	for path in `find /home/you -type f -size +100000c -print` do cd `dirname $path` || exit filename=`basename $path` split $filename $filename. mv -i $filename huge.$filename done

The find command will output pathnames like these:

/home/you/somefile
/home/you/subdir/anotherfile

(The absolute pathnames are important here. The cd would fail on the second pass of the loop if you use relative pathnames.) In the loop, the cd command uses dirname to go to the directory where the file is. The filename variable, with the output of basename, is used several places - twice on the split command line.

If that gives the error command line too long, replace the first lines with the two lines below. This makes a redirected-input loop (45.22):

find /home/you -type f -size +100000c -print |
while read path