grep command one liners

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Search for the given string in a single file

# grep "this" demo_file

Checking for the given string in multiple files

# grep "this" demo_*

Case insensitive search using grep -i

# grep -i "the" demo_file

Match regular expression in files

# grep "lines.*empty" demo_file

Checking for full words, not for sub-strings using grep –w If you want to search for a word, and to avoid it to match the substrings use -w option. Just doing out a normal search will show out all the lines.

Following example is the regular grep where it is searching for 'is'. When you search for 'is', without any option it will show out 'is', 'his', 'this' and everything which has the substring 'is'.

# grep -i "is" demo_file

Following example is the WORD grep where it is searching only for the word 'is'. Please note that this output does not contain the line 'This Line Has All Its First Character Of The Word With Upper Case', even though 'is' is there in the 'This', as the following is looking only for the word 'is' and not for 'this'.

# grep -iw "is" demo_file

Displaying lines before/after/around the match using grep -A, -B and -C

The following example prints the matched line, along with the 3 lines after it.

# grep -A 3 -i "example" demo_text

The following example prints the matched line, along with the 2 lines before it.

# grep -B 2 "single WORD" demo_text

The following example prints the matched line, along with the 2 lines before and after it.

# grep -C 2 "Example" demo_text

Highlighting the search using GREP_OPTIONS

As grep prints out lines from the file by the pattern / string you had given, if you wanted it to highlight which part matches the line, then you need to follow the following way

# export GREP_OPTIONS='--color=auto' GREP_COLOR='100;8'

# grep this demo_file

Searching in all files recursively using grep -r

# grep -r "ramesh" *

Invert match using grep -v

When you want to display the lines which does not matches the given string/pattern, use the option -v as shown below.

# grep -v "go" demo_text

# grep -i "go" demo_text

Display the lines which does not matches all the given pattern.

# grep -v -e "pattern" demo_text

Counting the number of matches using grep -c

When you want to count that how many lines matches the given pattern/string, then use the option -c as shown below,

# grep -c "go" demo_text

When you want do find out how many lines matches the pattern

# grep -c this demo_file

When you want do find out how many lines that does not match the pattern

# grep -v -c this demo_file

Display only the file names which matches the given pattern using grep -l

When you give multiple files to the grep as input, it displays the names of file which contains the text that matches the pattern, will be very handy when you try to find some notes in your whole directory structure.

# grep -l this demo_*

Show only the matched string

By default grep will show the line which matches the given pattern/string, but if you want the grep to show out only the matched string of the pattern then use the -o option.

It might not be that much useful when you give the string straight forward. But it becomes very useful when you give a regex pattern and trying to see what it matches as

# grep -o "is.*line" demo_file

Show the position of match in the line

When you want grep to show the position where it matches the pattern in the file, use the following options as

Syntax:

grep -o -b "pattern" file

$ cat temp-file.txt

12345

12345

# grep -o -b "3" temp-file.txt

2:3

8:3

Note: The output of the grep command above is not the position in the line, it is byte offset of the whole file.

Show line number while displaying the output using grep -n

To show the line number of file with the line matched. It does 1-based line numbering for each file. Use -n option to utilize this feature.

# grep -n "go" demo_text

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