grep

# Basic:
grep pattern file

# case nonsensitive research:
grep -i pattern file

# Recursively grep for string <pattern> in folder:
grep -R pattern folder

# Find files containing text
grep -Rl {search} {path}

# Find files containing text case insensitive
grep -Rli {search} {path}

# Getting pattern from file (one by line):
grep -f pattern_file file

# Find lines NOT containing pattern
grep -v pattern file

# You can grep with regular expressions
grep "^00" file  #Match lines starting with 00
grep -E "[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}" file  #Find IP add

# Find all files who contain {pattern} in the directory {directory}.
# This will show: "file:line my research"
grep -rnw 'directory' -e "pattern"

# Exclude grep from your grepped output of ps.
# Add [] to the first letter. Ex: sshd -> [s]shd
ps aux | grep '[h]ttpd'

# Colour in red {bash} and keep all other lines
ps aux | grep -E --color 'bash|$'

#   -B, --before-context=NUM  print NUM lines of leading context
#   -A, --after-context=NUM   print NUM lines of trailing context
#   -C, --context=NUM         print NUM lines of output context
grep -A 10 -B 10 pattern content