Several System Debug commands apply the concept of pattern matching. Commands such as CMDLIST, ENVLIST, FUNCLIST, MACLIST, PROCLIST, SYMLIST, and VARLIST support pattern matching in order to select which commands, functions, macro names, procedure names, symbol names, or variables are to be displayed.
In a similar manner, the FILTER environment variable is used to
selectively filter all System Debug output, displaying only those lines
that match the pattern or regular expression.
Regular expressions are used to find or match some specified text
within a large amount of surrounding text. A typical example is
to find all lines in a file that contain the word "computer."
A regular expression can be a single character, like the letter
"c" or a more elaborate construct built up from simple things
like the string "computer".
