Manipulating Text

The command line provides several powerful tools for manipulating text, whether it's in a file or being output from another command. In this section, we'll cover some of the most common tools for manipulating text.

cut

The cut command is used to extract sections from each line of a file or from piped input. It is primarily used to extract columns of data from a text file. For example, to extract the first three columns from a file named data.txt:

$ cut -f1-3 data.txt 

The -f option specifies the fields to extract, with -f1-3 extracting the first three fields.

sed

The sed command (short for "stream editor") is a powerful tool for manipulating text. It can be used to search for and replace text, delete lines, and more. The basic syntax of a sed command is:

$ sed 'command' filename 

For example, to replace all occurrences of "apple" with "orange" in a file named fruit.txt, use the following command:

$ sed 's/apple/orange/g' fruit.txt 

The s command specifies that sed should perform a substitution. The first occurrence of "apple" on each line is replaced with "orange", and the g modifier specifies that the substitution should be global (i.e., all occurrences on each line should be replaced).

awk

The awk command is a powerful tool for processing and manipulating text files. It is particularly useful for working with structured data, such as CSV files. The basic syntax of an awk command is:

$ awk 'pattern {action}' filename 

For example, to print the first and third columns of a CSV file named data.csv, use the following command:

$ awk -F',' '{print $1,$3}' data.csv 

The -F option specifies the field separator (in this case, a comma), and $1 and $3 specify the first and third columns, respectively.

tr

The tr command is used to translate or delete characters. It can be used to perform simple character-level substitutions or to remove characters from a file or piped input. For example, to remove all instances of the letter "e" from a file named text.txt, use the following command:

$ tr -d 'e' < text.txt 

The -d option specifies that tr should delete characters (in this case, the letter "e"). The < symbol redirects the contents of the file to tr's input.

These are just a few of the many text manipulation tools available on the command line. By combining these and other tools, you can quickly and easily process and manipulate text in a wide variety of ways.