Unix command ‘grep’

^ (Caret)        =    match expression at the start of a line, as in ^A.
$ (Question)     =    match expression at the end of a line, as in A$.
\ (Back Slash)   =    turn off the special meaning of the next character, as in \^.
[ ] (Brackets)   =    match any one of the enclosed characters, as in [aeiou].
                      Use Hyphen “-” for a range, as in [0-9].
[^ ]             =    match any one character except those enclosed in [ ], as in [^0-9].
. (Period)       =    match a single character of any value, except end of line.
* (Asterisk)     =    match zero or more of the preceding character or expression.
\{x,y\}          =    match x to y occurrences of the preceding.
\{x\}            =    match exactly x occurrences of the preceding.
\{x,\}           =    match x or more occurrences of the preceding.