From the Advanced Bash-Scripting Guide:
The $(COMMAND) form has superseded backticks for command substitution.
… When the fsck did that happen?! And why? Especially since the first example of command substitution given uses the old format with backticks. So nice of you to include that helpful tidbit as a goddamn footnote!
OK, I’ll stop ranting now…
It happened because backticks can’t be nested. With the new formatting I can write
rm -rf $(ls -la $(cat ~/dirList)) to delete all files in all the directories in the ~/dirList file. I couldn’t do that with backticks since rm -rf `ls -la `… looks like the command is “ls -la”.
Anyway, it happened around 2001.