Often in a large file, you have to look for a specific line of data buried somewhere in the middle of the file. Instead of manually scrolling through the entire file, you can let the grep command search for you. The command-line format for the grep command is:
# grep [options] pattern [file]
The grep command searches either the input or the file you specify for lines that contain characters that match the specified pattern. The output from grep is the lines that contain the matching pattern. Because of the popularity of the grep command, it has undergone lots of development changes over its lifetime. Many features have been added to the grep command. If you look over the man pages for the grep command, you’ll see how versatile it is.
If you want to reverse the search (output lines that don’t match the pattern), use the -v parameter:
$ grep -v t file1 one four five $
If you need to find the line numbers where the matching patterns are found, use the -n parameter:
$ grep -n t file1 2:two 3:three $
If you just need to see a count of how many lines contain the matching pattern, use the -c parameter:
$ grep -c t file1 2 $
If you need to specify more than one matching pattern, use the -e parameter to specify each individual pattern:
$ grep -e t -e f file1 two three four five $
grep Command Examples
1. To interpret PATTERN as an extended regular expression:
# grep --extended-regexp PATTERN # grep -E PATTERN
2. To interpret PATTERN as a list of fixed strings:
# grep -F PATTERN # grep --fixed-strings PATTERN
3. To interpret PATTERN as a basic regular expression:
# grep -G PATTERN # grep --basic-regexp PATTERN
4. To interpret PATTERN as a Perl regular expression:
# grep -P PATTERN # grep --perl-regexp PATTERN
5. To use PATTERN as the pattern:
# grep -e PATTERN, # grep --regexp=PATTERN
6. To obtain patterns from FILE, one per line:
# grep -f FILE, --file=FILE
7. To ignore case distinctions in both the PATTERN and the input files:
# grep -i PATTERN # grep --ignore-case PATTERN
8. To invert the sense of matching, to select non-matching lines:
# grep -v PATTERN # grep --invert-match PATTERN
9. To Select only those lines containing matches that form whole words:
# grep -w PATTERN # grep --word-regexp PATTERN
10. To Select only those matches that exactly match the whole line:
# grep -x PATTERN # grep --line-regexp PATTERN
11. To ignore the case:
# grep -y PATTERN
12. To Suppress normal output; instead print a count of matching lines:
# grep -c PATTERN # grep --count PATTERN
13. To display in color:
# grep --color PATTERN
14. To Suppress normal output; instead print the name of each input file, from out will not be expected:
# grep -L # grep --files-without-match
15. To Suppress normal output; instead print the name of each input file from which output have been printed:
# grep -l # grep --files-with-matches
16. To Quiet; do not write anything to standard output Exit immediately with zero status if any match is found:
# grep -q # grep --quiet # grep --silent
17. To Stop reading a file after NUM matching lines:
# grep -m NUM # grep --max-count=NUM
18. To Print only the matched (non-empty) parts of a matching line:
# grep -o PATTERN # grep --only-matching PATTERN
19. To Suppress error messages about nonexistent or unreadable files:
# grep -s PATTERN # grep --no-messages PATTERN
20. To Print the 0-based byte offset within the input file before each line of output:
# grep -b PATTERN # grep --byte-offset PATTERN
21. To Print the file name for each match:
# grep -H PATTERN # grep --with-filename PATTERN
22. To Suppress the prefixing of file names on output:
# grep -h PATTERN # grep --no-filename PATTERN
23. To Display input actually coming from standard input as input coming from file LABEL:
# grep -cd PATTERN | grep --label=mysearch -H PATTERN
24. To Prefix each line of output with the 1-based line number within its input file:
# grep -n PATTERN # grep --line-number PATTERN
25. To Make sure that the first character of actual line content lies on a tab stop:
# grep -T PATTERN # grep --initial-tab PATTERN
26. To Report Unix-style byte offsets:
# grep -u PATTERN # grep --unix-byte-offsets PATTERN
27. To Output a zero byte instead of the character that normally follows a file name:
# grep -Z PATTERN # grep --null PATTERN
28. To Print NUM lines of trailing context after matching lines:
# grep -A NUM PATTERN # grep --after-context=NUM PATTERN
29. To Print NUM lines of leading context before matching lines:
# grep -B NUM PATTERN # grep --before-context=NUM PATTERN
30. To Print NUM lines of output context:
# grep -C NUM PATTERN # grep --context=NUM PATTERN
31. To Process a binary file as if it were text:
# grep -a PATTERN /tmp/bin # grep -text PATTERN /tmp/bin
32. To assume that the file is of type TYPE:
# grep --binary-files=TYPE PATTERN
33. To If an input file is a device, FIFO or socket, use ACTION to process it:
# grep -D ACTION PATTERN # grep --devices=ACTION PATTERN
34. To If an input file is a directory, use ACTION to process it:
# grep -d ACTION PATTERN # grep --directories=ACTION PATTERN
35. To skip files whose base name matches GLOB:
# grep --exclude=GLOB PATTERN
36. To Skip files whose base name matches any of the file-name globs read from FILE:
# grep --exclude-from=FILE PATTERN
37. To Exclude directories matching the pattern DIR from recursive searches:
# grep --exclude-dir=DIR PATTERN
38. To Process a binary file as if it did not contain matching data:
# grep -I PATTERN
39. To Search only files whose base name matches GLOB:
# grep --include=GLOB
40. To Read all files under each directory, recursively:
# grep -r PATTERN # grep -R PATTERN
41. To Use line buffering on output:
# grep --line-buffered PATTERN
42. To If possible, use the mmap system call to read input, instead of the default read:
# grep --mmap PATTERN
43. To Treat the file(s) as binary:
# grep -U /tmp/file PATTERN # grep --binary /tmp/file PATTERN
44. To Treat the input as a set of lines:
# grep -z PATTERN # grep --null-data PATTERN
45. To display the help:
# grep -h
46. To print the version number of the grep:
# grep -V