grep

%  if [ `grep --quite failure resultfile` -eq 0 ];then echo " Step $stepFailed "; exit 3; fi             

Matched sections are displayed using $GREP_COLOR in the form ff[;bb]
where ff is the code used for the foreground and bb is used for the background.

Examples:
magenta on yellow 35;43 blue on cyan 34;46 red 31 (default)
Foreground: black 30, green 32, yellow 33, blue 34, magenta 35, cyan 36, white 37, red 31 (default)
Background: black 40, green 42, yellow 43, blue 44, magenta 45, underscore 4, [blink] 5, inverse 7
export GREP_COLOR="33;44"

Codes are not output when inappropriate (For example: to a file or pipe) unless when=always

grep --color=always birds logfile | more -r

 grep -c images *html |grep -v 0$ #dont show lines with 0 count
BackupStrageties.html:1
Characters.html:2
clonezilla.1.html:6
colors.html:3
css-box.html:4

Prefix lines with their line number, starting from the beginning of files.

Example:Show 2 lines before body with ++ between each occurance.

> while grep -B 2 -m 1 body ; do echo ++; done<index.html

With -v or --invert-match, stops after outputting num non-matching lines.

Used with commands find -print0, perl -0, sort -z, and xargs -0.

 gzip -cd foo.gz |grep --label=foo something

Causes all files to be read and passed to the matching mechanism verbatim.
If the file is actually a text file with ␍ or ␍␊ pairs, regular expressions with ^^† or $ ^† will not match.
Only under MS-Windows unless used with -b will not match.

By default, under MS-Windows, uses the first 32KB of the file to determine if a file is text.

type

• bracket expressions
  
  • in a list of characters enclosed by [ and ]
    Eaxmple: match from 1 to 9 spaces \{1,9\} .
  • nonmatching list
    ^  (caret) preceeding the expression matchs any character not in the list.
    For example:
    ^[abcdefghijklmnopqrstuvwxyz] matches a single non-lowercase character.
  • range expression
    Seperating two characters by - (hyphen) matches any single character that sorts between the two characters, inclusive.
    using the locale's collating sequence and character set.
    For example:
    [3-7] is equivalent to [34567].
    Many locales sort characters in dictionary order, in these locales [a-d] is typically equivalent [aBbCcDd] not [abcd].
    To obtain the traditional interpretation of bracket expressions ( where [a-d] is equivalent to [abcd]), use the C locale using set LC_ALL=C.
• named classes match a single character
  [:alpha:]   for [abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ]         NOT including Underscore ( _ ).
  [:lower:] . for [abcdefghijklmnopqrstuvwxyz]
  [:upper:]   for [ABCDEFGHIJKLMNOPQRSTUVWXYZ]
  [:digit:]   for [0123456789] synonym: \d (word)
  [:alnum:]   for [a-zA-Z0-9] synonyms : \w (word). \W NOT alnum.
  Frequently equivalent to [0-9A-Za-z].
  Depending on the C locale and the ASCII character encoding.
  [:xdigit:]   for [0123456789abcdefABCDEF]
[:print:]  
[:punct:]  
" # $ % & ' ( ) * + , - . / : ; < = > ? @ [ \ ] ^ _ ` { | } ~.
[:space:]  
  includes tab, newline, vertical tab, form feed, carriage return, and space.
  [:cntrl:]   In ASCII 0x00-0x1F & 0xFF.
  [:graph:]

  Brackets are part of the class names and must be included in addition to brackets that delimit a bracket expression.
  For example:
  /z[[:digit:]]z/ matches z3z but not z:z, zdz,…
  However:
  /z[:digit:]z/ Is a bracket expression list with an ignored second i and : .
  matches the strings : z:z, zdz, ziz, zgz, ztz (but not z3z)
  

  \s is a synonym for any white space character.

subexpression is defined using \(…\)

backreference \n, where n is a single digit, matches the substring previously matched by the n^th subexpression
Frequently on the right hand side of a substitute command

Special characters:
 To include ] place it first in the list. ][)(
 To include ^ place it anywhere but first. Otherwise it matches the beginning of the line.
 To include - place it last, lest it be considered a range
For example: [12345689] matches any single digit except 0 or 7.
Other metacharacters have no special meaning inside lists.

Precedence: Repetition, concatenation, alternation.
A subexpression overrides precedence rules.