egrep command in Unix

Updated May 31, 2023

Introduction to egrep command in Unix

The egrep command in Unix shell scripting is owned by the family of the grep command that is used for searching and matching a specific pattern in Unix. egrep works similarly to grep -E (grep Extended regex’) do. egrep generally searches a specific file or even line to line or prints the line in the input file, which has the scanned regular expression. It takes the selected pattern as a regular expression and will finally print the output out the lines, which is the same as the specified pattern. For any case, if there are a number of files with the same matching pattern, it will give the output showing the file names matching the pattern for each line.

What can we do from egrep command?

There are many options to search and match a specific pattern in Unix with the help of egrep command. We can perform n number of search patterns and get the output as the egrep command requires.

Below are a few options that can be used to search and match the pattern:

PATTERN Selection and Interpretation:

-E, –extended-regexp	PATTERN is an extended regular expression.
-F, –fixed-strings	PATTERN is a set of newline-separated strings.
-G, –basic-regexp	PATTERN is a basic regular expression (default).
-P, –perl-regexp	PATTERN is a Perl regular expression.
-e, –regexp=PATTERN	Use PATTERN for matching.
-f, –file=FILE	Obtain PATTERN from FILE.
-i, –ignore-case	Ignore case distinctions.
-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 a newline.

Output Control:

-m, –max-count=NUM	Stop after NUM selected lines.
-b, –byte-offset	Print the byte offset with output lines.
-n, –line-number –line-buffered	Print line number with output lines. Flush output on every line.
-H, –with-filename	Print file name with output lines.
-h, –no-filename –label=LABEL	Suppress the file name prefix on output. Use LABEL as the standard input file name prefix.
-o, –only-matching	Show only the part of a line matching PATTERN.
-q, –quiet, –silent	Suppress all normal output.
-a, –text	Equivalent to –binary-files=text.
-d, –directories=ACTION	How to handle directories; ACTION is ‘read’, ‘recurse’, or ‘skip’.
-r, –recursive	Like –directories=recurse.
-R, –dereference-recursive –include=FILE_PATTERN–exclude=FILE_PATTERN–exclude-from=FILE–exclude-dir=PATTERN	Likewise, but follow all symlinks. Search only files that match FILE_PATTERN. Skip files and directories matching FILE_PATTERN. Skip files matching any file pattern from FILE. Directories that match PATTERN will be skipped.
-L, –files-without-match	Print only names of FILEs with no selected lines.
-l, –files-with-matches	Print only names of FILEs with selected lines.
-c, –count	Print only a count of selected lines per FILE.
-T, –initial-tab	Make tabs line up (if needed).
-Z, –null	Print 0 byte after the FILE name.

Context control:

-B, –before-context – NUM	Print NUM lines of leading context.
-A, –after-context – NUM	Print NUM lines of trailing context.
-C, –context – NUM	Print NUM lines of output context.
-NUM	Same as –context=NUM.
–color[=WHEN],	Use markers to highlight the matching strings;
–colour[=WHEN]	WHEN is ‘always’, ‘never’, or ‘auto’
-U, –binary	do not strip CR characters at EOL (MSDOS/Windows).

Syntax of egrep:

egrep command would need the option to mention the matching pattern and the filename to search and match the way in the file.

Below is the syntax for egrep command:

egrep [options] [pattern] [files..]

Examples of using egrep commands in Shell Scripting

Let us consider there is a file named ‘testing.txt’ which contains the below data, and we will be taking this file and show examples below:

Code:

cat testing.txt

Output:

Example #1: Option -c

It counts the number of lines in the files that match the pattern.

Syntax:

egrep -c [pattern] file_name

Code:

egrep -c student testing.txt

Output:

Example #2 Option -v

This option helps print the lines that do not match the pattern specified in the input parameter.

Syntax:

egrep -v [pattern] filename

Code:

egrep -v student testing.txt

Output:

Example #3: Option -i

It displays the lines in the file that match the input pattern while ignoring the case of alphabets.

Syntax:

egrep -i [pattern] filename

Code:

egrep -i student testing.txt

Output:

Example #4: Option -w

It displays only the lines which have the complete word in it.

Syntax:

egrep -w [pattern] filename

Code:

egrep -w graduate testing.txt

Output:

Example #5: Option -x

With this option, we can only print the entire line if it is given in the input file.

Syntax:

egrep -x [line] filename

Code:

egrep -x '101 sonia graduate 65000' testing.txt

Output:

Example #6: Option -m

With this option, it will continue to search the pattern until the number of counts mentioned in the input reaches the number mentioned in the parameter.

Syntax:

egrep -m [number] [pattern] filename

Code:

egrep -m 3 graduate testing.txt

Output:

Example #7: Option -r

It recursively scans for the matched pattern given in the input parameter. It will give you the information in the file that matches the input pattern.

Syntax:

egrep -r [pattern] filename

Code:

egrep -r '*grad*' testing.txt

Output:

Example #8: Option ‘OR’

We can have an option for ‘OR’ using a pipe ‘|’ symbol. When choosing between two options, ‘OR’ is used.

Syntax:

egrep 'option1|option2' filename

Code:

egrep 'sonia|teja' testing.txt

Output:

Example #9: Option -l

This option will help print only the filenames with the matched pattern or string inside it. It will only give you the filename that has the matched string.

Syntax:

egrep -l 'string' filename_pattern

Code:

egrep -l sonia *.txt

Output:

Example #10: Option -o

Instead of printing the entire line in a file, we can print the specified pattern from the file. The output will display the number of times the word appeared in the specified file.

Syntax:

egrep -o [pattern] filename

Code:

egrep -o student testing.txt

Output:

Conclusion

The egrep command in Unix shell scripting is owned by the family of the grep command that is used for searching and matching a specific pattern in Unix. egrep works similar to grep -E (grep Extended regex’) do. egrep generally search a specific file or even line to line or prints the line in the input file, which has the scanned regular expression.

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