Filtering data refers to selecting a subset of data based on certain conditions and/or criteria. We will cover several methods to filter data in Bash, including

1. Using grep command
2. Using awk command
3. Using sed command

Filtering Data Using the grep Command

The grep command is a powerful tool for searching for patterns in text files. For example, the following command will display all lines in the file “file.txt” that contain the word “bash”:

grep "bash" file.txt

The following will be the output.

The grep command also has several options that can be used to modify its behavior. For example, the -v option will display all lines in the file that do not contain the pattern:

grep -v "bash" file.txt

The following will be the output.

Filtering Data Using the awk Command

The awk command is a pattern-matching and processing language. It can be used to filter data based on specific conditions. For example, the following command will display the third field of each line in the file “file.txt” that contains the word “error”:

awk '/bash/ {print $3}' file.txt

The following will be the output.

The awk command uses patterns specified between slashes (/), to match lines in the input file. The code block between the braces ({}) is executed for each line that matches the pattern. In this case, the third field of each line ($3) is printed.

Filtering Data Using the sed Command

The sed command is a stream editor that can perform text transformations on an input stream. For example, the following command will display all lines in the file “file.txt” that contain the word “bash”, with the word “error” highlighted in red:

sed -e 's/bash/\x1b[31merror\x1b[0m/g' file.txt

The following will be the output.

The sed command uses a script, specified with the -e option, to perform transformations on the input stream. In this case, the script uses a substitution command (s) to replace all occurrences of the word “error” with a highlighted version.