`comm`

Compares two files line by line.

With no options, produces 3 columns in output:

column 1 contains lines unique to file 1;
column 2 contains lines unique to file 2;
column 3 contains lines common to both files.

Comparisons honor the rules specified by 'LC_COLLATE'.

TL;DR
Further readings
Sources

TL;DR

Usage

# Print only lines present in both file1 and file2.
comm -12 'path/to/pre-sorted/file1' 'path/to/pre-sorted/file2'

# Print unique lines of file1 which are not present in file2.
comm -23 'path/to/pre-sorted/file1' 'path/to/pre-sorted/file2'
comm -23 <(sort -u 'path/to/file1') <(sort -u 'path/to/file2')

# Check the whole content of file1 is present in file2.
test $(comm -23 'path/to/pre-sorted/file1' <(sort -u 'path/to/file2') | wc -l) -eq 0
[[ $(comm -23 <(sort -u 'path/to/file1') 'path/to/pre-sorted/file2' | wc -l) -eq 0 ]]

Real world use cases

# List security groups not used by EC2 instances in AWS.
comm -23 \
  <( aws ec2 describe-security-groups --query 'SecurityGroups[*].GroupId' --output 'text' | tr '\t' '\n' | sort ) \
  <( \
    aws ec2 describe-instances --query 'Reservations[*].Instances[*].SecurityGroups[*].GroupId' --output 'text' \
    | tr '\t' '\n' | sort | uniq \
  )

Sources

All the references in the further readings section, plus the following:

2.1 KiB Raw Blame History

comm

TL;DR

Further readings

Sources

2.1 KiB

Raw Blame History

`comm`