dirname is a standard computer program on Unix and Unix-like operating systems. When dirname is given a pathname, it will delete any suffix beginning with the last slash ('/') character and return the result. dirname is described in the Single UNIX Specification and is primarily used in shell scripts.
History
The version of dirname bundled in GNU coreutils was written by David MacKenzie and Jim Meyering.[1] The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities.[2] The dirname command has also been ported to the IBM i operating system.[3]
Usage
The Single UNIX Specification for dirname is:
dirname string
string
- A pathname
Examples
dirname will retrieve the directory-path name from a pathname ignoring any trailing slashes
$ dirname /home/martin/docs/base.wiki
/home/martin/docs
$ dirname /home/martin/docs/.
/home/martin/docs
$ dirname /home/martin/docs/
/home/martin
$ dirname base.wiki
.
$ dirname /
/
Performance
Since dirname accepts only one operand, its usage within the inner loop of shell scripts can be detrimental to performance. Consider
while read file; do
dirname "$file"
done < some-input
The above excerpt would cause a separate process invocation for each line of input. For this reason, shell substitution is typically used instead
or if relative pathnames need to be handled as well
if [ -n "${file##*/*}" ]; then
echo "."
else
echo "${file%/*}";
fi
Note that these handle trailing slashes differently than dirname.
Misconceptions
We might think that paths that end in a trailing slash are a directory. But actually, the trailing slash represents all files within the directory.
/home/martin/docs/.
The correct way to represent a path as a directory is with a trailing slash and a period.[according to whom?][citation needed]
