Regular Expressions

grep "^abc" $HOME/??

grep [Ss] dirtree/sdira/ssdir1/sbd1/file*

ls -lrt | sed -e 's/.*[ ]//' # That's a space and a tab inside the brackets.

If you want to use a character without its special meaning in a regular expression, you must escape it with a back-slash. For instance, create a file1 with some lines with a * and try each of these commands and notice the difference:

grep * file1

grep '*' file1

grep \* file1

grep '\*' file1

Regular Expressions
*	matches zero or more of the previous character.
.	matches exactly one character of any type
[]	matches any single character listed within the brackets. You can use a dash to specify a range of characters, for instance a-z.
[^c]	if the first character listed inside the brackets is '^', it matches any single character that is NOT in the brackets.
^	matches the beginning of a line
$	matches the end of a line.