'history -s' in a script doesn't work

Question

I'm relatively new to linux, and trying furiously to lean bash, and eventually zsh. Anyway, for the moment this has me stumped:

#!/bin/bash
history -s "a_string"

.... doesn't work. I've tried a dozen variations on the idea, but nothing cuts it. Any ideas?

Answer 1

The subshell is not interactive, and therefore doesn't save the history or the parent shell doesn't reload history.

Typical ways around this:

1. use an alias instead of a script

      alias doit='history -s "a_string"'  
      unalias doit
   

2. use a shell function instead of script

      function doit() { 
           echo "A function is a lot like a script"
           history -s "but operates in a subshell only when a bash command does (piping)" 
      }
      unset doit
   

3. source the script, instead of executing it in a subshell

   source ./myscript.sh
   . ./myscript.sh   # equivalent shorthand for source
   

Answer 2

$HISTFILE and $HISTFILESIZE are not set when running a script like this. Once you set $HISTFILE you can read and write the history as you like.