Shell – Prepending a Timestamp to Each Line of Command Output

Bellow is an example playbook, which executes a number of simple tasks.

---
 - hosts: localhost
   tasks:
    - name: say hi
      shell: echo "Hello, World!"

    - name: do df -h
      shell: df -h
      register: space

    - name: show the output of df -h
      debug: var=space

    - name: do free -m
      shell: free -m
      register: memory
      ignore_errors: yes

    - name: show memory stats
      debug: var=memory

    - name: create /tmp/"hostname"_bkp
      file: dest=/tmp/{{ ansible_nodename }}_bkp state=directory

    - name: create files
      file: dest=/tmp/{{ ansible_nodename }}_bkp/file{{ item }} state=touch
      with_items:
       - 1
       - 2
       - 3
       - 4
       - 5

It creates a directory and files at the desired location. You can also set ownership, permissions, which fit better your requirements.

ansible_nodename is an ansible fact (a variable), which gets collected at the beginning of a play.

You can see more information about the ansible file module here. Please have a look at the other ansible modules - they are plenty, easy to learn and powerful.

Let's suppose that the script generating the output is called generate. Then, to display the number of seconds it takes for it to generate each line:

$ generate | ( t0=$(date +%s); while read -r line; do t1=$(date +%s); echo " $((t1-t0)) $line"; t0=$t1; done )
 2 foo
 0 foo
 5 foo
 3 foo

The same commands spread out over multiple lines looks like:

generate | ( t0=$(date +%s)
    while read -r line
    do
        t1=$(date +%s)
        echo " $((t1-t0)) $line"
        t0=$t1
    done
    )

Alternatively, for convenience, we can define a shell function that contains this code:

timer() { t0=$(date +%s); while read -r line; do t1=$(date +%s); echo " $((t1-t0)) $line"; t0=$t1; done; }

We can use this function as follows:

$ generate | timer
 0 foo
 2 foo
 4 foo
 3 foo

How it works

• t0=$(date +%s)

  This captures the current time at the start of the script in seconds-since-epoch.

• while read -r line; do

  This starts a loop which reads from standard input

• t1=$(date +%s)

  This captures the time in seconds-since-epoch at which the current line was captured.

• echo " $((t1-t0)) $line"

  This prints out the time in seconds that it took for the current line.

• t0=$t1

  This updates t0 for the next line.

• done

  This signals the end of the while loop.