Grep

grep - Pretty much a search function. Prints lines matching a pattern.

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Examples:

cat [file] | grep "word"         # Prints any line with "word"

grep -i                          # Ignore case senisitivity *i is for INSENSITIVE*

grep -irl [word] [dir]                  # Ignore case distinctions,  Read all files under each directory, recursively, Suppress normal output; 

grep [word] [in file/dir]        # Searches up "word" in that file or dir

grep [x$] [file]                 # Searches the file with any word that ENDS "x" in it. Variation: [xxx$] 
multiple letter search that ends with these letters.

grep [^x]                        # Searches the file with any word that STARTS with "x"

grep [^x$]                       # Searches lines that ONLY has 'x' in it.

grep "x.*" [file]                # Searches up a letter, doesn't matter if it is in the beginnging or end of the line.

grep -i "^l.*rse$" [file]        # Searches file for anything starts with "l", anything in the middle, and ends in "rse"

grep -i '[ab]' [file]            # Searches all lines that have a 'a' or 'b' in it.

grep [Xx]avier                   # Searches lines that contain [X]avier or [x]avier

grep [wrd] [file] | grep "word"  grepception.

grep -v '^x' [file]              # '-v' means inverse, so this means, search all lines that DO NOT start with 'x'

grep '[^brackets]'               # Search all lines with anything THAT IS NOT IN THE BRACKETS

grep --color=always              # use color to highlight

Search for two words at once

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grep -E 'word1|word2' *.doc

Count the number of occurrences

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grep's -o will only output the matches, ignoring lines; wc can count them:

grep -o 'needle' file | wc -l

Search for a string and show the following lines before/after it

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you can use -B num to set how many lines before the match and -A num for the number of lines after the match.

grep -B 3 -A 2 foo README.txt