awk field extraction in scripts in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does $1 represent in an awk command?

$1 represents the first field (or column) of the current line being processed by awk.

beginner

How do you print the third field of each line using awk?

Use awk '{print $3}' filename to print the third field of each line.

beginner

What is the default field separator in awk?

The default field separator is any whitespace (spaces or tabs).

intermediate

How can you change the field separator to a comma in awk?

Use the -F option like this: awk -F',' '{print $2}' filename to split fields by commas.

intermediate

In a script, how do you store the second field of a line into a variable using awk?

You can use command substitution: var=$(awk '{print $2}' filename). This stores the second field output into the shell variable var.

What does awk '{print $1}' file.txt do?

A Prints the whole line

B Prints the last field of each line

C Prints the first field of each line in file.txt

D Deletes the first field

This command prints only the first field of each line in the file.

How do you tell awk to split fields by a colon :?

A awk -S':' '{print $2}' file

B awk -F':' '{print $2}' file

C awk --field=':' '{print $2}' file

D awk -D':' '{print $2}' file

The -F option sets the field separator to colon.

If a line is apple orange banana, what does $3 represent?

A banana

B orange

C apple

D The whole line

$3 is the third field, which is 'banana'.

Which command prints the second and fourth fields separated by a space?

A awk '{print $2+$4}' file

B awk '{print $2.$4}' file

C awk '{print $2-$4}' file

D awk '{print $2, $4}' file

Using a comma in print outputs fields separated by a space.

What is the output of awk -F',' '{print $1}' on the line red,green,blue?

A red

B green

C blue

D red,green,blue

With comma as separator, $1 is 'red'.

Explain how awk extracts fields from a line and how you can change the field separator.

Think about how words in a sentence are split by spaces or other characters.

Describe how to use awk inside a bash script to save a specific field from a file into a variable.

Remember how you capture command output in bash.