Ubuntu14.04 can't use `pbcopy` command.
However, there is an alternative way.
The command is `xsel`.
The command `xsel` needs `--clipboard` and `--input` as options.
xsel --clipboard --input
can copy on clipboard.
I can replace `xsel --clipboard --input` with `pbcopy`.
In particular, I use `alias` command.
alias pbcopy='xsel --clipboard --input'
I can hereby use as `pbcopy` command.