Dirname: Difference between revisions

dirname

Example of dirname command
Developer(s)	Various open-source and commercial developers
Operating system	Unix, Unix-like, IBM i
Platform	Cross-platform
Type	Command
License	coreutils: GPLv3+

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. 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. The dirname command has also been ported to the IBM i operating system.

Usage

The Single UNIX Specification for dirname is:

dirname string

string

A pathname

$ 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

 echo "${file%/*}";

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.

See also

• List of Unix commands
• basename
• Path (computing)

External links

• dirname: return the directory portion of a pathname – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
• dirname(1) – Linux User Commands Manual
• dirname(1) – OpenBSD General Commands Manual