Info about grep / examples

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Usage: grep [OPTION]... PATTERN [FILE]... (a few options / a few files can be passed at once)

Most used (by me):

-r    recursive

-i    ignore case distinctions

-NUM  print NUM lines of output context`  
     --colour[=WHEN]    use markers to highlight the matching strings`
                        WHEN is 'always', 'never' or 'auto'

Seems useful

  -R, --dereference-recursive  likewise, but follow all symlinks
      --include=FILE_PATTERN  search only files that match FILE_PATTERN
      --exclude=FILE_PATTERN  skip files and directories matching FILE_PATTERN
      --exclude-from=FILE   skip files matching any file pattern from FILE
      --exclude-dir=PATTERN  directories that match PATTERN will be skipped.
  -B, --before-context=NUM  print NUM lines of leading context
  -A, --after-context=NUM   print NUM lines of trailing context
  -H, --with-filename       print the file name for each match
  -T, --initial-tab         make tabs line up (if needed)
  -h, --no-filename         suppress the file name prefix on output
      --label=LABEL         use LABEL as the standard input file name prefix
  -c, --count               print only a count of matching lines per FILE
  -m, --max-count=NUM       stop after NUM matches
  -L, --files-without-match  print only names of FILEs containing no match
  -l, --files-with-matches  print only names of FILEs containing matches
  -o, --only-matching       show only the part of a line matching PATTERN
  -f, --file=FILE           obtain PATTERN from FILE
  -w, --word-regexp         force PATTERN to match only whole words
  -x, --line-regexp         force PATTERN to match only whole lines
  -z, --null-data           a data line ends in 0 byte, not newline
  -v, --invert-match        select non-matching lines
  -n, --line-number         print line number with output lines
      --line-buffered       flush output on every line
  -q, --quiet, --silent     suppress all normal output
      --binary-files=TYPE   assume that binary files are TYPE;
                            TYPE is 'binary', 'text', or 'without-match'
  -a, --text                equivalent to --binary-files=text
  -I                        equivalent to --binary-files=without-match

Not used by me (copy-paste from help)

Regexp selection and interpretation:
  -E, --extended-regexp     PATTERN is an extended regular expression (ERE)
  -F, --fixed-strings       PATTERN is a set of newline-separated strings
  -G, --basic-regexp        PATTERN is a basic regular expression (BRE)
  -P, --perl-regexp         PATTERN is a Perl regular expression
  -e, --regexp=PATTERN      use PATTERN for matching

Miscellaneous:
  -s, --no-messages         suppress error messages
  -V, --version             display version information and exit
      --help                display this help text and exit

Output control:
  -b, --byte-offset         print the byte offset with output lines
  -d, --directories=ACTION  how to handle directories;
                            ACTION is 'read', 'recurse', or 'skip'
  -D, --devices=ACTION      how to handle devices, FIFOs and sockets;
                            ACTION is 'read' or 'skip'
  -Z, --null                print 0 byte after FILE name

Context control:
  -U, --binary              do not strip CR characters at EOL (MSDOS/Windows)
  -u, --unix-byte-offsets   report offsets as if CRs were not there
                            (MSDOS/Windows)

`PATTERN` is, by default, a basic regular expression (BRE)

'egrep' means 'grep -E'.  'fgrep' means 'grep -F'.
Direct invocation as either 'egrep' or 'fgrep' is **deprecated**.
When FILE is -, read standard input.  With no FILE, read . if a command-line
-r is given, - otherwise.  If fewer than two FILEs are given, assume -h.
Exit status is 0 if any line is selected, 1 otherwise;
if any error occurs and -q is not given, the exit status is 2.

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Sources:

grep --help