Grep ‘global regular expression print’, is a powerful command on Linux & Unix-like operating systems used to search a pattern. It processes text line by line and prints line(s) which match a specified pattern.
Examples:
File file.txt with below content:
This is first line
This is second line
This is third line
This is fourth LINE
This is fifth LINE
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Command
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Output
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To find line pattern (case-sensitive) in file.txt
$ grep ‘line’ file.txt
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To find ne pattern (case-insensitive) in file.txt
$ grep -i ‘ne’ file.txt
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To find is word (case-sensitive) in file.txt
$ grep -iw ‘is’ file.txt
Here, is in This is not matched because it is not a complete word
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To get one line after of matched pattern
$ grep -A1 ‘second’ file.txt
To get one line before of matched pattern
$ grep -B1 ‘second’ file.txt
To get one line before & after of matched pattern
$ grep -C1 ‘second’ file.txt
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To count the lines with matched pattern
$ grep -c ‘line’ file.txt
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How do I use grep?
To search multiple files with the grep command, insert the filenames you want to search, separated with a space character. The terminal prints the name of every file that contains the matching lines, and the actual lines that include the required string of characters.
How do I use grep to find words?
The easiest of the two commands is to use grep’s -w option. This will find only lines that contain your target word as a complete word. Run the command “grep -w hub” against your target file and you will only see lines that contain the word “hub” as a complete word.
What is the use of grep command in Linux?
The grep filter searches a file for a particular pattern of characters, and displays all lines that contain that pattern. The pattern that is searched in the file is referred to as the regular expression (grep stands for globally search for regular expression and print out).
How do you start grep?
That is, remove the * , which basically tells grep , find zero or more occurances of the ^1 expression. In other words: match the lines that start with a 1, or not. You can use a shell glob to list all files that start with 1 .
How do you grep special characters?
To match a character that is special to grep –E, put a backslash ( \ ) in front of the character. It is usually simpler to use grep –F when you don’t need special pattern matching.
How do you grep multiple lines?
How do I grep for multiple patterns?
- Use single quotes in the pattern: grep ‘pattern*’ file1 file2.
- Next use extended regular expressions: egrep ‘pattern1|pattern2’ *. py.
- Finally, try on older Unix shells/oses: grep -e pattern1 -e pattern2 *. pl.
- Another option to grep two strings: grep ‘word1\|word2’ input.
What are grep patterns called?
Grep Regular Expression
A regular expression or regex is a pattern that matches a set of strings. A pattern consists of operators, constructs literal characters, and meta-characters, which have special meaning. GNU grep supports three regular expression syntaxes, Basic, Extended, and Perl-compatible.
How do you use grep and Egrep?
grep and egrep does the same function, but the way they interpret the pattern is the only difference. Grep stands for “Global Regular Expressions Print”, were as Egrep for “Extended Global Regular Expressions Print”.
How do you grep double quotes in Linux?
So, you have to use different approaches:
- Use double quotes: grep “‘type’ => ‘select'” file.
- If you prefer needlessly complex solutions: grep “‘”type”‘”\ =\>\ “‘”select”‘” file.
- You can always search for any single character instead of specifying the single quotes: grep ‘.type. => . select.’ file.
How do I grep and save a file?
grep -n “test” * | grep -v “mytest” > output–file will match all the lines that have the string “test” except the lines that match the string “mytest” (that’s the switch -v ) – and will redirect the result to an output file.
How do I grep all files in a directory?
By default, grep would skip all subdirectories. However, if you want to grep through them, grep -r $PATTERN * is the case. Note, the -H is mac-specific, it shows the filename in the results. To search in all sub-directories, but only in specific file types, use grep with –include .
How do I grep recursively in a directory?
To recursively search for a pattern, invoke grep with the -r option (or —recursive ). When this option is used grep will search through all files in the specified directory, skipping the symlinks that are encountered recursively.
Why grep is not working?
The arguments to grep are a search expression and a list of files. So grep * ends up using the first file name as the search expression. You are looking for the first file’s name (as a regular expression) in the other files. As you have discovered, an empty search expression matches all input lines.
How do I reduce grep output?
The quiet option ( -q ), causes grep to run silently and not generate any output. Instead, it runs the command and returns an exit status based on success or failure. The return status is 0 for success and nonzero for failure.
What is grep option?
The grep utility searches one or more files, line by line, for a pattern, which can be a simple string or another form of a regular expression. The grep utility takes various actions, specified by options, each time it finds a line that contains a match for the pattern.
How do you grep dollar sign?
For example, grep uses a dollar sign as a special character matching the end of a line — so if you actually want to search for a dollar sign, you have to precede it by a backslash (and include the whole search string in single quotes).
What options can be used with grep command?
The grep command supports a number of options for additional controls on the matching:
- -i: performs a case-insensitive search.
- -n: displays the lines containing the pattern along with the line numbers.
- -v: displays the lines not containing the specified pattern.
- -c: displays the count of the matching patterns.