This script appears to be part of a Bash shell...

This script appears to be part of a Bash shell script that handles revoking Access Control Lists (ACLs) for a list of topics. Here's what it does, step by step:

Breakdown:

1. echo "Revoking ACLs for matching topics..."
   This prints a message to indicate the start of the process.

2. if [ -n "$MATCHING_TOPICS" ]; then
   It checks if the variable MATCHING_TOPICS is non-empty (contains any topic names). If MATCHING_TOPICS is empty, it skips the revocation process.

3. for topic in $MATCHING_TOPICS; do
   Iterates over the topics listed in the MATCHING_TOPICS variable, processing each one individually.

4. echo "Revoking ACLs for topic: $topic"
   Prints a message for each topic being processed.

5. Retrieve all principals associated with a topic:

   PRINCIPALS=$(list_acls | grep "topic=$topic" | grep -o 'User:CN=[^,]*' | cut -d'=' -f2 | sort | uniq)
   

   • Runs a command (list_acls) that presumably lists ACLs for all topics.
   • Filters the output to include only entries related to the current topic (grep "topic=$topic").
   • Uses grep -o 'User:CN=[^,]*' to extract and isolate strings like User:CN=....
   • Extracts the principal name after the = character with cut -d'=' -f2.
   • Ensures unique sorted principal names using sort | uniq.
     This produces a list of unique principals (users) who have access to the current topic.

6. for principal in $PRINCIPALS; do
   Iterates over each principal (user) who has access to the topic.

7. Revoke ACLs for each principal:

   echo "Revoking ALL access for User:CN=$principal on $topic"
   revoke_access_topic "$principal" "All" "$topic"
   

   • Prints a message indicating that all access is being revoked for the user on the specific topic.
   • Calls a function or command revoke_access_topic to remove the access for the given principal on the topic. The "All" argument suggests that all types of access (read, write, etc.) are being revoked.

8. Else condition:
   If MATCHING_TOPICS is empty:

   echo "No topics found, skipping ACL revocation."
   

   Indicates there are no topics to process, so it skips any revocation.

Summary of the Code's Functionality

• The code revokes all ACLs for specific topics listed in the MATCHING_TOPICS variable.
• For each topic, it identifies all principals (users) who have access to the topic.
• For each principal, it revokes all types of access to that topic.
• If no topics are found (MATCHING_TOPICS is empty), it skips the process.

This script is likely part of an administrative tool for managing ACLs in a system with topics and user permissions, such as Apache Kafka.