bashvariablestimestamp

Create timestamp variable in bash script


I am trying to create a timestamp variable in a shell script to make the logging a little easier. I want to create the variable at the beginning of the script and have it print out the current time whenever I issue echo $timestamp. It proving to be more difficult then I thought. Here are some things I've tried:

timestamp="(date +"%T")" echo prints out (date +"%T")

timestamp="$(date +"%T")" echo prints the time when the variable was initialized.

Other things I've tried are just slight variations that didn't work any better. Does anyone know how to accomplish what I'm trying to do?


Solution

  • In order to get the current timestamp and not the time of when a fixed variable is defined, the trick is to use a function and not a variable:

    #!/bin/bash
    
    # Define a timestamp function
    timestamp() {
      date +"%T" # current time
    }
    
    # do something...
    timestamp # print timestamp
    # do something else...
    timestamp # print another timestamp
    # continue...
    

    If you don't like the format given by the %T specifier you can combine the other time conversion specifiers accepted by date. For GNU date, you can find the complete list of these specifiers in the official documentation here: https://www.gnu.org/software/coreutils/manual/html_node/Time-conversion-specifiers.html#Time-conversion-specifiers