Complex sentence: Some versions of Unix and Linux contain Bash system startup scripts, generally under the/etc directories, which are called as part of standard Bash initialization but which themselves may read in other startup files in a different order than that in the documented Bash startup sequence.
Split into simpler sentences: Some versions of Unix and Linux contain Bash system startup scripts, generally under the/etc directories. Bash calls these as part of its standard initialization, but other startup files can read them in a different order than the documented Bash startup sequence.