agrep: filter the input lines with a criteria
The whole lines that accord to the criteria will be printed

Parameters:
-i: case insensitivity
-w: look for whole words
-d {chars}: set the delimiter characters (separators for whole words)
-or: or relation between the criterias
  show the lines that contain any of the search words
  (default relation: and - show the lines that contain each of the search
  words)
-not: negate the result of the search relation
-nand: not-and relation (show each line except the ones containing each search
  word)
-nor: not-or relation
-xor: xor relation (show the lines where only one of the search words has
  been found)
-nxor: not-xor relation
-r {regexp}: use regular expression
-ln: line numbers
-not: invert the criteria
-e {expression}: use the Eval-based expression (variable: 'line')
-oe {expression}: format the output lines with the given expression
-f {file}: use the file as input
-p[rev] {n}: show the previous n lines before a match
-n[ext] {n}: show the next n lines after a match
-fetch/-pf {n}: fetch n lines (store in buffer for expression usage)
  If this is specified, the 'lines' runtime string array can be used to
  refer to the previous lines (array index: 0 - current line, 1 - previous
  line, 2 - second prev and so on). The array size is n.
-c[ont]: print each line after a valid match
-m[ax]: the max number of matches
-v {variable_definition}: define a runtime variable
-q {expression}: specifiy an expression that is evaluated for each incoming
  line (before the search criteria for the current line is evaluated)
-pq {expression}: expressions that are evaluated after the evaluation of the
  marching criteria

Runtime variables for the expressions:
-line: the contents of the current incoming line
-lines: the string array of the previous lines (see -pf)
-lc: line counter, the number of the current line (starting with 0)
-mc: match count
-match: the logical value (0/1) of the current line match

Examples:
agrep -f help.txt Apple -ln
  -> find the word 'Apple' in the file
  possible output: 1: I ate an apple\n10: Steve Jobs established Apple in 1976

... | agrep Windows API -or
  -> find each line that contains either 'Windows' or 'API'

... | agrep -e "substring(line, 5, 9)=='jacko'"
  -> find the lines where 'jacko' is at he given position

... | agrep -e "strtok(line, '|', 1) []= 'apple'" -oe "strtok(line, '|', 3)"
  -> find the lines where the second token contains 'apple', the output will
     contain only the fourth token of the lines

... | agrep -e -fetch 1 "strcont(line, 'apple') && strcont(lines[1], 'plum')"
  -> match if the current line contains 'apple' and the previous line
     contains 'plum'

... | agrep -v "af<int>" -q "af = af | strcont(line, 'apple')" -e "af &&
      strcont(line, 'plum')"
  -> find each line containing 'plum' only after the first line that contains
     'apple' (the expression after '-q' is evaluated for each line -> 'af'
     becomes true (1) after the first 'apple'-rich line, therefore the
     evaluating expression gives true value only after such a line)

... | agrep -e "lc % 5 == 0"
  -> list each 5th line

... | agrep -e "line []= 'apple' && mc < 10"
  -> list the first ten lines containing 'apple'

... | agrep -v "m<int>" -q "aif(line []= 'apple', m, 1)" -e "m"
  -> list the lines beginning with the one that contains 'apple'

... | agrep -v "m<int>" -pq "aif(line []= 'apple', m, 1)" -e "m"
  -> list the lines _after_ the one that contains 'apple'