grep

# To search a file for a pattern:
grep <pattern> <file>

# To perform a case-insensitive search (with line numbers):
grep -in <pattern> <file>

# To recursively grep for string <pattern> in <dir>:
grep -R <pattern> <dir>

# Read search patterns from a file (one per line):
grep -f <pattern-file> <file>

# Find lines NOT containing pattern:
grep -v <pattern> <file>

# Set how many lines to show before (-B) and after (-A) pattern:
grep -B 3 -A 2 <pattern> <file>

# To 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

# To find all files that match <pattern> in <dir>
grep -rnw <dir> -e <pattern>

# To 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|$'