working principle
grep command in one or more search for a character mode file, if the pattern contains spaces, you must enclose it in quotes. grep command, the mode may be a quoted string, or a single word. Located mode after all the words are treated as a file name. grep output to the screen, it does not make any modifications or changes in the input file. grep returns an exit status of 0, indicating success. Exit status is 1, indicating not found. If you can not find the file specified, the exit status is 2. You can use a regular expression pattern.
grep support common to all the regular expression, such as: basic regular, extended regular and Perl regular; by adjusting the corresponding parameter to specify the use of regular expressions, also called derived grep, such as: grep using -e parameter will grep into egrep, grep will use the -f argument becomes fgrep; of course, a regular expression can be turned off effect.
grammar
grep [OPTION]... PATTERN [FILE]...
parameter
| Regular support |
description |
| -E，--extended-regexp | Open extended regular mode, the equivalent of using the egrep command |
| -F，--fixed-strings | Close regular expression character string regarded as the direct matching PATTERN |
| -G，--basic-regexp | By default, enable basic regular expression |
| -P，--perl-regexp | Open perl-compatible regular mode, use perl language in regular matches, I do not represent, and therefore does not involve |
| -e，--regexp=PATTERN | This option is for the "-" is not supported by default because the grep pattern contains - match "." Use -e to avoid error. |
| -f，--file=FILE | The PATTERN written to the specified file, this option, you can call the file PATTERN to match the target file |
| -i，--ignore-case | Match, ignore case be |
| -w，--word-regexp | The PATTERN as a word (before and after the letter is not a non-ending), equivalent to PATTERN added to the "\ bPATTERN \ b" to delimitation. |
| -x，--line-regexp | Pattern Matching entire row |
| -v，--invert-match | Excluded PATTERN, displaying the remaining content is not matched to the line |
Regular refer to : https://www.cnblogs.com/guge-94/p/10678890.html
| Improve performance options |
description |
| -c，--count | PATTERN to match the number of successful content |
| -r，--recursive | Recursive queries matching sub-directory file, when the target file type is a directory; -R option is -r way links |
| -s, --no-messages | Does not output an error message |
| -m，--max-count=NUM | The maximum number of output lines matched to the content, such as three lines comprising the PATTERN, only two output lines, can -m 2 |
| -n，--line-number | Show Line Numbers |
| -H，--with-filename | The output file name, before the contents of the line, when the target file is more than the default |
| -h，--no-filename | No output filename |
| -o，--only-matching | PATTERN to match only output is the content rather than the default output the entire line |
| -q，--quiet | Information is not normal output |
| -L | When the target file is grep multiple files, the results are output in the "File name: content matching rows" form. -L only will not contain matching lines of output file name. And -v similar. |
| Content control line | description |
| --color | Implemented {auto never | | always} disposed highlight color mode and can be used |
| -B，--before-context=NUM | The first few lines of print match |
| -A，--after-context=NUM | After a few lines of print match |
| -C，--context=NUM | Print a few lines before and after the match |
Examples
1, the output line b in the same file in a file
grep -f a b
2, the output b in a document file different rows
grep -v -f a b
3, a plurality of pattern matching
echo "a bc de" |xargs -n1 |grep -e 'a' -e 'bc'
4, remove blank lines or blank lines http.conf file number starting with #
grep -E -v "^$|^#" /etc/httpd/conf/httpd.conf
5, the beginning of the match case-insensitive word
echo "A a b c" |xargs -n1 |grep -i a
6, show only the matching string
echo "this is a test" |grep -o 'is'
7, the output of the matching results of the first five
seq 1 20 |grep -m 5 -E '[0-9]{2}'
8, how many rows match statistics
seq 1 20 | grep -c -E ' [0-9] {2} '
9, b character matches the beginning of the line
echo "a bc de" |xargs -n1 |grep '^b'
10, line matches the end of de characters and output matching lines
echo "a ab abc abcd abcde" |xargs -n1 |grep -n 'de$'
11, recursive search / etc directory that contains the conf file extension ip
grep -r '192.167.1.1' /etc --include *.conf
12, exclude search bak file suffix
grep -r ' 192.167.1.1 ' / opt --exclude * .bak
13, to exclude from a file in the file
grep -r '192.167.1.1' /opt --exclude-from file
14, 41 or 42 matching digital
seq 41 45 | grip -E ' 4 [12] '
15, matching at least two characters
seq 13 | grep -E ' [0-9] {2} '
16, matching at least two-character words, word up to 3 characters
echo "a ab abc abcd abcde" |xargs -n1 |grep -E -w -o '[a-z]{2,3}'
17, matching all IP
ifconfig |grep -E -o "[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}"
18, the matching result, and print the row 3
seq 1 10 |grep 5 -A 3
19, print matching results and the first three rows
seq 1 10 |grep 5 -B 3
20, the matching result and print lines before and 3
seq 1 10 | grip 5 -C 3
21, no error output
grep -s 'a' abc
22, the normal output is not displayed
grep -q 'a' a.txt
23, search for content in Gzip compressed file
zgrep -i error /var/log/syslog.2.gz