I am receiving an error from an application I am running.
The error looks like this:
john@john-replacement:~/Desktop/yarbu-1.4.8/bin$ sudo yarbu-engine --VERBOSE
/usr/local/bin/yarbu-engine: line 996: cd: /usr/local/bin/../../etc/yarbu/conf/default: No such file or directory
What do the dots mean in /usr/local/bin/../../etc/ ?
The ../ is notation for "the parent directory" so, in the case you presented:
/usr/local/bin/../../etc/yarbu/conf/default
The system will resolve that as:
/usr/etc/yarbu/conf/default
It's the same as if you were in the directory /usr/local/bin and you then typed cd .. twice, you would now be in the /usr directory.
You can verify this yourself:
$ cd /usr/local/bin
$ pwd
/usr/local/bin
$ cd /usr/local/bin/../../../
$ pwd
/
cd .., which sanitizes the path using realpath. If one of the path components of /usr/local/bin is a symbolic link which points somewhere else, then realpath sanitization will not point to the same directory. e.g. if /usr/local is a synlink to /opt/unspecified, /usr/local/bin/../../etc/yarbu/conf/default is resolved as /opt/etc/yarbu/conf/default, but realpath sanitizes it as /usr/etc/yarbu/conf/default. Just nitpicking here. In contrast, ls ../../etc/yarbu/conf/default while in /usr/local/bin works.
In addition to gabe's answer, which is nice:
The unix command readlink will always return the real path of a file or directory: readlink -f /usr/local/bin/../../etc/ will return /usr/etc/.
The command also resolves symbolic links. For example on my system, readlink -f /usr/bin/java returns /usr/lib/jvm/jdk-7.15-oracle-x64/jre/bin/java. Both use cases are very helpful for scripts.
Btw: .. (and also . which refers to the directory where you are) are not unix specific. The same will also work under at least all dos/windows, mac, linux/unix/bsd based operating systems.
