Added grep to reference

_commands/scripting/grep.md

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+---
+---
+
+grep
+---
+`grep`  is a linux command that processes text and prints any lines that match a specified pattern. `grep` stands for **G**lobal **R**egular **E**xpression **P**rint.
+
+```bash
+$grep [OPTIONS] PATTERN [FILE...]
+```
+
+<!--more-->
+## Examples
+Imagine a file called test.txt:
+```
+Linux is fun
+C4CS is cool
+CS is awesome
+```
+Running grep with the pattern "C4CS" will return the line all lines containg that pattern.
+```bash
+$grep C4CS test.txt
+C4CS is cool
+```
+
+## Regular Expressions
+The real power of grep comes from its ability to use regular expressions as a pattern. For the folowing examples consider a dictionary called dict.txt.
+### Bracket Expressions
+A bracket expression is a list of characters enclosed by [ and ]. A bracket expression will  match any single character in the list.
+```bash
+$grep c[aou]t dict.txt
+cat
+cot
+cut
+```
+bracket expressions can also be used with a hypen to match a range. [a-e] is equivlent to [abcde]. And [0-9] is equivlent to [0123456789].
+### Negating a Bracket Expression
+A carat (^) at the begining of a bracketed expression will match characters not in the list.
+```bash
+$grep c[^u]t dict.txt
+cat
+cot
+```
+### Anchoring
+The ^ symbol is used to match at the begining of the string. The $ symbol is used to match at the end of the string.
+```bash
+$grep t dict.txt
+# returns all words containing an 't'
+$grep ^t dict.txt
+# returns all words begining with 't'
+$grep t$ dict.txt
+# returns all words ending in 't'
+### Wildcard
+The . symbol is used as a wildcard. It can match any single character.
+```bash
+$grep .oat dict.txt
+boat
+coat
+goat
+moat
+```
+### Repetition
+The ?  symbol means the preceding item may be matched zero or one times. ab?c matches both "ac" and "abc".
+The * symbol means the preceding item may be matched zero or more times. ab*c mathces "ac", "abc", "abbc", and so on.
+The + symbol means the preceding item may be matched one or more times. ab+c matches "abc", "abbc", "abbbc", and so on.
+{n} means the preceding item is matched exactly n times. a{5} matches "aaaaa".
+{n,} means the preceding item is matched n or more times. a{3,} matches "aaa", "aaaa", and so on.
+{,n} means the preceding item is matched at most n times. a{,3} matches "","a","aa","aaa".
+{n,m} means the preceding item is matched at least n times and at most m times. a{1,3} matches "a","aa","aaa".
+
+## grep Options
+
+### -i, --ignore-case
+Uses case insesitive matching for the PATTERN.
+### -v, --invert-match
+Prints lines that do not match the PATTERN.
+### -c, --count
+Does not print matching lines, instead prints the number of matching lines.
+Can be used in combination with -v as -cv to print the number of non-matching lines.
+### -q, --quiet, --silent
+Do not print anything. Exit 0 if any match is found, even if there is an error.
+### -H, --with-filename
+Print the filename for eaach match. This option is default when provided with more than one file.
+### -h, --no-filename
+Suppress output of file names. This is default when provided with only one file to search
+### -n, --line-number
+Prefix each line of output with the 1-based line number within its file.
+### -R, -r, --recursive
+Read all files under a directory