grep vs awk - Part 2

In this article, we will see more awk alternatives for the frequently used grep commands. This is in continuation to thegrep vs awk - Part 1. Let us consider a sample file as shown below:

$ cat file Unix linux Uniix Solaris AIX ArchLinux Ubuntu

1. Search for a pattern present in a variable

$ x="Linux" $ grep "$x" file Linux

The variable x contains the search pattern. Using grep, the variable can directly be used.

$ awk -v var="$x" '$0 ~ var' file Linux

In awk, the variable cannot be used directly. It needs to be passed to awk from shell using the -v option. More about the variable passing to awk .

2. Search for lines beginning with a specific pattern: $ grep '^S' file Solaris

The ^ symbol is used to search for lines which begin with. In this example, we are trying to search for lines which are beginning with is S.

$ awk '/^S/' file Solaris

3. Search for lines ending with a specific pattern:

$ grep 'x$' file Unix Uniix Linux ArchLinux

The $ symbol is used to search for matches which are ending with.

$ awk '/x$/' file Unix Uniix Linux ArchLinux

4. To search for a exact word in a file:

$ grep -w Linux file Linux

The option -w is used in grep for the specific word search. The pattern ArchLinux did not retutrn because 'Linux' is just part of the the word.

$ awk '{for(i=1;i<=NF;i++)if($i=="Linux"){print;}}' file Linux

In awk, we need to loop over the columns and compare the value against every column.

5. To get count of lines matching pattern:

$ grep -c ix file 2

The -c option of grep gives the count of lines matching the pattern. The "ix" pattern is matched in 2 lines.

$ awk '/ix/{x++}END{print x}' file 2

In awk, whenever the pattern "ix" is matched, a variable x is incremented. At the end of the file processing, x contains the count of lines matching the pattern.

6. Search for a pattern which exactly matches the whole line:

$ grep -x Linux file Linux

grep has the -x option for matching exact matches.

$ awk '/^Linux$/' file Linux

In awk, we use the ^ (beginning with) and $(ending with) meta characters to search for the exact match.

7. Search for non-empty lines or lines containing atleast one character:

$ grep . file Unix Linux Uniix Solaris AIX ArchLinux Ubuntu

The . matches any character. Since empty line does not have any, it does not match.

$ awk NF file Unix Linux Uniix Solaris AIX ArchLinux Ubuntu

NF indicates number of fields. Since an empty line will have NF as 0, it does not get matched.

8. Extract part of the line instead of the entire line:

$ grep -o "..$" file ix ux ix is IX tu

By default, grep prints the entire line which matches the pattern. Using -o option only a part of string can be extracted. .. extracts 2 characters, ..$ extracts 2 characters from the end of the line.

$ awk 'NF{print substr($0,length-1);}' file ix ux ix is IX tu

awk uses the sub-string function(substr) to do the extraction.

Let us consider another sample file with 2 columns in it:

$ cat file Unix 2 Linux 3 Uniix 4 Solaris 5

9. Extract the 2nd column from the lines containing a specific pattern :

$ grep Uni file | cut -d" " -f2 2 4

grep extracts the lines containing the pattern, and cut extracts only the 2nd column.

$ awk '/Uni/{print $2}' file 2 4

In awk, searching a pattern and printing a particular column all are done as part of the same command.

10. Extracting first 3 characters from lines containing a specific pattern:

$ grep x file | cut -c 1-3 Uni Lin Uni

grep extracts lines containing the pattern 'x' and cut cuts the 1st three columns.

$ awk '/x/{print substr($0,1,3)}' file Uni Lin Uni

To know& learn more about the awk , you can refer to theawk related articles.