1.grep Introduction
grep (Global search Regular expression (RE) and print out of the line, full search of regular expressions and print out rows) is a powerful text search tool that uses regular expressions to search for text. and print out the matching lines. The grep family of Unix includes grep, Egrep, and Fgrep. Egrep and Fgrep commands are only a small difference from grep. Egrep is the extension of grep, which supports more re metacharacters, and fgrep is fixed grep or fast grep, which regards all the letters as words, that is, the metacharacters in the regular expression represents the literal meaning back to itself, no longer special. Linux uses the GNU version of grep. It is more powerful and can use the Egrep and FGREP functions with the-G,-e,-f command line options.
grep works in such a way that it searches for a string template in one or more files. If the template includes spaces, it must be referenced, and all strings after the template are treated as filenames. The results of the search are sent to the screen without affecting the contents of the original file.
grep can be used for Shell scripting, because grep describes the status of the search by returning a status value, or 0 if the template search succeeds, or 1 if the search is unsuccessful, or 2 if the searched file does not exist. We can use these return values to do some automated text processing work.
Function Description: Find the string that matches the condition in the file.
Syntax: grep [-abcefghhillnqrsvvwxy][-a][-b][-c] [-d][-e][-f][--help][template style] [file or directory ...]
Additional notes:
The grep directive is used to find the file that contains the specified template style, and if the contents of a file are found to conform to the specified template style, the preset grep command displays the column containing the template style. If no file name is specified, or if the given file name is "-", the grep instruction reads the data from the standard input device.
Parameters
-A or--text do not ignore binary data.
-A or--after-context= in addition to displaying the column that conforms to the template style, and displays the contents after that column.
-B or--byte-offset indicates the bit number of the first character of the column before displaying the column that conforms to the template style.
-B or--before-context= in addition to displaying the column that conforms to the template style, and displays the contents before the column.
-C or--count calculates the number of columns that conform to the template style.
-C or--context= or--in addition to displaying the column that conforms to the template style, and displays the contents before the column.
-D or--directories= You must use this parameter when you specify that you want to find a directory instead of a file, otherwise the GREP directive returns information and stops the action.
-E or--regexp= specifies the string as the template style for finding the contents of the file.
-E or--extended-regexp uses the template style as an extended normal notation.
-F or--file= specifies a template file with the contents of one or more template styles that let grep find the contents of the file that match the template criteria, in the form of a template style for each column.
-F or--fixed-regexp treats the template style as a list of fixed strings.
-G or--basic-regexp use the template style as normal notation.
-H or--no-filename does not indicate the file name that the column belongs to until it displays the column that conforms to the template style.
-H or--with-filename indicates the file name that the column belongs to before it displays the column that conforms to the template style.
-I or--ignore-case ignores the difference in the case of characters.
-L or--file-with-matches lists file names that match the file contents to the specified template style.
-L or--files-without-match lists file names that do not conform to the specified template style.
-N or--line-number indicates the column number of the column before displaying the column that conforms to the template style.
-Q or--quiet or--silent does not display any information.
-R or--recursive the effect of this parameter is the same as specifying the "-D recurse" parameter.
-S or--no-messages does not display an error message.
-V or--revert-match reverse lookup.
-V or--version displays version information.
-W or--WORD-REGEXP displays only the columns that match the whole word.
-X or--LINE-REGEXP displays only columns that are eligible for all columns.
-Y the effect of this parameter is the same as specifying the "-i" parameter.
--help online Help.
2. grep regular expression meta-character set (base set)
^
The start of the anchoring line is as follows: ' ^grep ' matches all lines that begin with grep.
$
The end of the anchoring line is as follows: ' grep$ ' matches all rows ending with grep.
Match a non-newline character such as: ' GR.P ' matches gr followed by an arbitrary character followed by P.
*
Match 0 or more previous characters such as: ' *grep ' matches all one or more spaces followed by the grep line. * Use together to represent any character.
[]
Matches a specified range of characters, such as ' [Gg]rep ' matches grep and grep.
[^]
Matches a character that is not within the specified range, such as: ' [^a-fh-z]rep ' matches a letter that does not contain a-r and t-z, immediately following the line of the Rep.
(..)
Mark matching characters, like ' (Love) ', and Love is labeled as 1.
<
Anchor the beginning of a word, such as: '
>
Anchors the end of a word, such as ' grep> ', that matches a line containing a word that ends with grep.
X
Repeat characters x,m times, such as: ' 0 ' matches rows containing 5 O.
X
Repeat the character X, at least m times, such as: ' O ' matches at least 5 rows of O.
X
Repeat the character X, at least m times, no more than n times, such as: ' O ' matches the line of 5--10 O.
W
Match literal and numeric characters, that is, [a-za-z0-9], such as: ' Gw*p ' matches with G followed by 0 or more literal or numeric characters, followed by P.
W
The inverted form of w, matching one or more non-word characters, such as the dot period, and so on.
B
The word lock, such as: ' BGREPB ' only matches grep.
3. Meta-character expansion set for Egrep and GREP-E
+
Matches one or more previous characters. such as: ' [a-z]+able ', matching one or more lowercase letters followed by able strings, such as loveable,enable,disable, etc.
?
Matches 0 or more previous characters. such as: ' Gr?p ' matches the GR followed by one or no characters, then the line of P.
A|b|c
Match A or B or C. such as: grep|sed matching grep or sed
()
Grouping symbols, such as: Love (able|rs) ov+ match loveable or lovers, matching one or more ov.
X,x,x
function with X,x,x
4. POSIX character class
POSIX (The Portable Operating System Interface) adds special character classes to the character encodings in different countries, such as [: Alnum:] is another notation for a-za-z0-9. You can place them in the [] number to be a regular expression, such as [a-za-z0-9] or [[: Alnum:]]. grep under Linux supports POSIX character classes in addition to Fgrep.
[: Alnum:]
Literal numeric characters
[: Alpha:]
Literal characters
[:d Igit:]
numeric characters
[: Graph:]
Non-null characters (non-whitespace, control characters)
[: Lower:]
lowercase characters
[: Cntrl:]
Control characters
[:p rint:]
Non-null characters (including spaces)
[:p UNCT:]
Punctuation
[: Space:]
All whitespace characters (new lines, spaces, tabs)
[: Upper:]
Uppercase characters
[: Xdigit:]
hexadecimal digits (0-9,a-f,a-f)
5. grep command Options
-?
Show matching rows up and down at the same time? Line, such as: grep-2 pattern filename Displays the top and bottom 2 rows of a matching row.
-b,--byte-offset
Prints the block number where the line is printed before the matching line.
-C,--Count
Only the number of matched rows is printed and the matching content is not displayed.
-F File,--file=file
Extract the template from the file. An empty file contains 0 templates, so nothing matches.
-h,--no-filename
When searching multiple files, the matching file name prefix is not displayed.
-i,--ignore-case
ignores case differences.
-q,--quiet
Cancels the display, returning only the exit status. 0 indicates that a matching row was found.
-l,--files-with-matches
Prints a list of files that match the template.
-l,--files-without-match
Prints a list of files that do not match the template.
-n,--line-number
Prints the line number in front of the matching line.
-s,--silent
does not display an error message about a file that does not exist or cannot be read.
-v,--revert-match
Anti-retrieval, displaying only rows that do not match.
-w,--word-regexp
If referenced, the expression is searched as a single word.
-v,--version
Displays software version information.
6. Example
To use a good grep this tool, in fact, is to write a regular expression, so here does not have all the functions of grep to explain, only a few examples, explain a regular expression of the wording.
$ ls-l | grep ' ^a '
Filters the contents of the Ls-l output through a pipeline, displaying only the lines that begin with a.
$ grep ' test ' d*
Displays all rows that contain test in a file that begins with D.
$ grep ' test ' AA bb cc
Displays the line that matches test in the aa,bb,cc file.
$ Grep ' [A-z] ' AA
Displays all rows that contain a string of at least 5 consecutive lowercase characters for each string.
$ grep ' W (es) t.* ' AA
If West is matched, es is stored in memory, labeled 1, and then searched for any character (. *) followed by another ES (), which is found to display the line. If you use Egrep or GREP-E, do not use the "" number to escape, directly written as ' W (es) t.* ' on it.
Search for text files with ' grep '
If you want to find a string in several text files, you can use the ' grep ' command. ' grep ' searches the text for the specified string.
Suppose you are searching for a file with the string ' magic ' in the '/usr/src/linux/documentation ' directory:
$ grep magic/usr/src/linux/documentation/*
sysrq.txt:* How do I enable the Magic SysRq key?
sysrq.txt:* How does I use the Magic sysrq key?
Where the file ' Sysrp.txt ' contains the string and discusses the functionality of SYSRQ.
By default, ' grep ' searches only the current directory. If there are many subdirectories under this directory, ' grep ' is listed in the following form:
Grep:sound:Is a Directory
This may make the output of ' grep ' difficult to read. There are two ways to solve this problem:
Explicit Requirements Search subdirectories: grep-r
or Ignore subdirectories: grep-d Skip
Of course, if you anticipate that you have a lot of output, you can go through the pipeline and take it to ' less ' to read:
$ grep magic/usr/src/linux/documentation/* | Less
This makes it easier for you to read.
One thing to note is that you need to provide a way to filter the file (search for all files in *). If you forget, ' grep ' will wait until the program is interrupted. If you encounter such a situation, press and then try again.
Here are some interesting command-line arguments:
Grep-i pattern Files: Search by case-insensitive. The default case is case-sensitive,
Grep-l pattern Files: Lists only the matching file names,
Grep-l pattern Files: Lists mismatched file names,
Grep-w pattern files: matches only the entire word, not part of the string (such as matching ' magic ', not ' magical '),
Grep-c number pattern files: matching contexts display [number] lines, respectively,
grep pattern1 | PATTERN2 files: Displays rows that match pattern1 or pattern2.
grep pattern1 Files | grep pattern2: Displays rows that match both PATTERN1 and pattern2.
Here are some special symbols for searching:
\ mark the beginning and end of the word respectively.
For example:
grep man * will match ' Batman ', ' manic ', ' man ', etc.
grep ' \
grep ' \ ' matches only ' man ', not ' Batman ' or ' manic ' and other strings.
' ^ ': refers to a matching string at the beginning of the line,
' $ ': refers to a matching string at the end of the line,
If you are not accustomed to command line arguments, try the graphical interface ' grep ', such as Rexgrep. This software provides syntax for and, or, not, and beautiful buttons. If you just need a clearer output, try Fungrep.
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Common command syntax for grep
1. Double quote quotes and single quote references
When you enter a string parameter in the grep command, it is best to enclose it in double quotation marks. For example: "MyString". There are two reasons to do this, one is to avoid being misunderstood as a shell command, and two is to find a string of multiple words, for example: "Jet Plane", if it is not enclosed in double quotation marks, then the word plane will be mistaken for a file, the query results will return "file does not exist" error message.
When calling a variable, you should also use double quotes, such as grep "$ MYVAR" file name, if not, the
No results were returned.
Single quotes should be used when calling pattern matching. [[email protected]]# echo ' grep 123 111.txt ' (#注意是反单引号)
2. The commonly used grep options are:
-C outputs only the count of matching rows.
-I is case-insensitive (only for single-character).
-H does not display a file name when querying multiple files.
-L Only output file names that contain matching characters when querying multiple files.
-N Displays matching lines and line numbers.
-S does not display error messages that do not exist or have no matching text.
-V Displays all lines that do not contain matching text.
3. Special – Query in multiple files
$ grep "Sort" *.doc (Find string "s O r T" in #在当前目录下所有. D o C file)
$ grep "Sort It" * (#或在所有文件中查询单词 "sort It")
All of the following examples refer to querying in a single file
4. Row matching
$ grep-c "48″DATA.F
$4 (#grep返回数字4, meaning there are 4 lines that contain the string "4 8″. )
$ grep "48″DATA.F (#显示包含" 4 8″ string of 4 lines of text)
5. Displays the number of rows that satisfy the matching pattern:
[Email protected] oid2000]# grep-n 1234 111.txt
1:1234
3:1234ab
6. Exact match
[[email protected] oid2000]# grep "1234\>" 111.txt
1234
7. Query for empty rows, and query for rows that begin or end with a condition.
Use a combination of ^ and $ to query for blank lines. Use the-n parameter to display the actual number of rows
[[email protected] oid2000]# grep-n "^$" 111.txt (return result 2: #说明第二行是空行)
[Email protected] oid2000]# grep-n "^ABC" 111.txt (#查询以abc开头的行)
[Email protected] oid2000]# grep-n "abc$" 111.txt (#查询以abc结尾的行)
8. Match Special characters and query for characters that have special meanings, such as $. ' "* [] ^ | \ + ? , you must add \ before a specific character.
[[email protected] oid2000]# grep "\." 111.txt (#在111. txt in the query contains "." of all rows)
[[email protected] oid2000]# grep "my\.conf" 111.txt (#查询有文件名my. c o n F lines)
9. Querying the Directory
[Email protected] oid2000]# ls-l |grep "^d" (#如果要查询目录列表中的目录)
[Email protected]t oid2000]# ls-l |grep "^d[d]" (#在一个目录中查询不包含目录的所有文件)
[Email protected]]# ls-l |grpe "^d.....x. X "(#查询其他用户和用户组成员有可执行权限的目录集合)
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Can simply be summed up as follows:
The grep command is a line filter tool under Linux, its parameters are numerous, the following is a description of the role of each parameter, we hope to help.
grep-Print lines matching a pattern (the line that matches the style is listed)
Syntax: grep [Options]
PATTERN [FILE ...]
grep is used to correspond to a portion of the file in the text, or when no file is specified, the standard input is compared. In a preset scenario, grep lists the line that matches the style. In addition, there are two programs that are grep-type, egrep and Fgrep. Where Egrep is equivalent to GREP-E, Fgrep is equivalent to grep-f.
Parameters
1.-A Num,--after-context=num
In addition to listing rows that are compliant, and after NUM lines are listed.
Example: $ grep-a 1 Panda file
(Search for panda-style lines from file and show the following 1 lines of the row)
2.-A or--text
grep is originally a search text file, if the binary file as the target of the search, it will display the following message: Binary file binary file name matches and then end. If you add the-a parameter, you can treat the binary file as a text file search, which is equivalent to the--binary-files=text parameter.
Example: (Search for panda styles from the binary archive mv)
(Error!!!)
$ grep Panda MV
Binary file MV Matches
(This means that the file has match, see--BINARY-FILES=TYPE)
$
(Correct!!!)
$ grep-a Panda MV
3.-B Num,--before-context=num
is relative to-a num, but this parameter is a num line that displays in addition to the line that matches and appears before it.
Example: (Searching for a panda-style line from file and displaying the first 1 rows of that row)
$ grep-b 1 Panda file
4.-C [NUM],-num,--context[=num]
Lists rows that are outside the line and lists the upper and lower num lines, with the default value of 2.
Example: (list file In addition to the line containing the panda style and out of its top and bottom 2 lines)
(To change the default value, you can change num directly)
$ grep-c[num] Panda file
5.-B,--byte-offset
The total number of bytes in the text before the style is listed:
Exemple: $ grep-b Panda file
The results appear similar to the following:
0:panda
66:pandahuang
123:panda03
6.--binary-files=type
This parameter type is preset to binary (binary), and if it is searched in the normal way, there are only 2 kinds of results:
1. If there is a match: Display binary file binary file name matches
2. If no match is in place: nothing is shown.
If type is Without-match, this parameter is encountered, and grep will assume that the binary file does not contain any search styles, the same as the-I parameter. If Tpye is text, grep treats the binary as a text file, the same as the-a parameter.
Warning:--binary-files=text If the output is a terminal, some unnecessary output may be generated.
7.-C,--count
Does not display matching style rows and displays only the total number of rows that are eligible.
If you add-V,--invert-match, the parameter shows the total number of rows that are not met.
8.-D ACTION,--directories=action
If the input file is a folder, use the action to process the folder.
The default action is read, which means that the folder will be treated as a generic file; If the action is skip (skip), the folder will be skipped by grep: If the action is recurse (recursive), grep will read all the files under the folder, which is equivalent to the-R Parameters.
9.-E,--extended-regexp
Use regular expressions to interpret styles.
.-E PATTERN,--regexp=pattern
Make the style a partern, usually used to avoid partern-start.
-F FILE,--file=file
The style to be searched in advance is written to a file, one line at a style, and then the file is searched. An empty file indicates no style to search for, so there will be no match.
Example: (NewFile for search style files)
$grep-F NewFile File
-G,--basic-regexp
Treats a style as a basic rule-representation interpretation. (This is a preset)
-H,--with-filename
The path is displayed if there is a path that matches the name of the file before each line that matches the style.
Example: (Search for Panda styles in file and testfile)
$grep-H panda file./testfile
File:panda
./testfile:panda
-H,--no-filename
is similar to the-h parameter, but does not show the path at output.
--help.
Generate a short help message.
I.-I
grep enforces that this binary file does not contain any search styles, as in the--binary-files=without-match parameter.
Example: $ grep-i Panda mv
.-I,--ignore-case
Ignores case, contains the style to be searched and the file to be searched.
Example: $ grep-i Panda mv
-L,--files-without-match
Does not display the usual output results, but instead shows the file names that are not compliant.
.-L,--files-with-matches
Does not display the usual output results, only the matching file name is displayed.
--mmap.
If possible, use the MMAP system call to read the input instead of the preset read system call. In some situations,--mmap can produce better performance. However,--mmap can cause undefined behavior (including core dump) if the file is shortened in operation, or I/O errors occur.
-N,--line-number
The uplink number is marked before the line is displayed.
Example: $ grep-n Panda file
The display results are similar to the following:
Line number: Content that matches the line
-Q,--quiet,--silent
No general output is displayed. See-S or--no-messages
-r-r,--recursive
Recursively, reads all the files under each folder, which is equivalent to the-D recsuse parameter.
-S,--no-messages
Does not display error messages about non-existent or unreadable.
Small bet: Unlike GNU grep, traditional grep does not conform to the POSIX.2 protocol because it lacks the-Q parameter, and his-s parameter behaves like the-Q parameter of GNU grep.
Shell script tends to migrate traditional grep, bypassing the-Q and-s parameters, and limiting the output to/dev/null.
Posix:
Defines the features that UNIX and unix-like systems need to provide.
-V,--version
Displays the version number of grep to the standard error.
When you return the bugs about grep, the grep version number must be included.
.-V,--invert-match
Displays all except the search style line.
.-W,--word-regexp
The search style is treated as a word search, and the line that matches the "word" exactly is listed.
X.-X,--line-regexp
The search style is treated as a single line of search, and lines that fully match the "line" are listed.
case: Searching for Volume_down strings, ignoring *.git files grep-rwn--exclude-dir=*.git "Volume_down".
A detailed description of the grep command under Linux
