The output of
# ls
and
# echo $(ls)
are the same. What exactly does the $ sign and the parenthesis mean?
Also, what is going on a technical level that causes the output of these two commands to be the same?
This is command substitution for bash.
Command substitution allows the output of a command to replace the
command itself. Command substitution occurs when a command is enclosed
as follows:
$(command) or
`command`
http://www.gnu.org/software/bash/manual/bashref.html#Command-Substitution
More:
http://tldp.org/LDP/abs/html/commandsub.html
http://wiki.bash-hackers.org/syntax/expansion/cmdsubst
And a good example similar to your question:
http://bashshell.net/shell-scripts/using-command-substitution-in-a-bash-shell-script/
