3.3. Command Substitution
In almost all cases in this document, I use the $(<command>)
convention for command substitution: that is,
means "substitute the output from the date +%H%M
command here." This works in Bash 2.0+. In some older versions of Bash,
prior to 1.14.7, you may need to use backquotes (`date
+%H%M`). Backquotes can be used in Bash 2.0+, but are being
phased out in favor of $(), which nests better. If you're using an earlier
version of Bash, you can usually substitute backquotes where you see $().
If the command substitution is escaped (ie. \$(command) ), then use
backslashes to escape BOTH your backquotes (ie. \'command\' ).