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If a run the watch command containing an alias, it will not expand the alias. I have tried both with single quote and double quotes, in fact given the following alias:
# alias ll
alias ll='ls -l --color=tty'
The following command will fail
# watch ll
sh: ll: command not found
Shouldn't command line expansion work in this case?
Aliases are only expanded as the first argument, or after another alias with a trailing space on the end of the command.
From bash's help alias:
A trailing space in VALUE causes the next word to be checked for alias substitution when the alias is expanded.
To do this, try the following:
alias watch='watch '
alias ll='ls -l --color=tty'
watch ll
Bear in mind that some versions of watch strip colours by default, on some versions this can be stopped by using --color or -G.
watch because the alias has to be the next word, whereas watch needs its arguments before the command to run. If you tried watch -n 10 <alias>, bash won't expand the alias. To work around it, you need an alias that includes the options you want (e.g., `alias watch-10='watch -n 10 '), still with a trailing space.
Maybe we could manually expand the alias before watch sees it?
watch $(alias ll | cut -d\' -f2)
The output of alias ll looks like:
$ alias ll
alias ll='ls -lAGh'
So we set cut's delimeter to be single quote, and cut the 2nd field, leaving:
ls -lAGh
ie the expanded alias. That then forms the args given to watch.
function watcha {
watch $(alias "$@" | cut -d\' -f2)
}
Then,
watcha ll
works as desired. This is awful and will fail in all sorts of situations. Sorry.
There's a custom program to handle this over at github.com/antonmedv/watch. It supports multiple shells. Of course because it's custom software to install it's OK for your normal computers but not helpful on random servers you might be connected to. Here's how I run it so I can watch my zsh aliases and functions:
function watch-zsh() {
WATCH_COMMAND='zsh -ci' /usr/local/bin/watch "$@"
}
I thought here basic problem is while executing watch, the argument is given to "sh -c" which means if alias ll is not defined in sh(dash shell's) environment then it will not expand it. But I was wrong and this is not the case, Chris' answer above is right.
watch 'alias ll="ls -l --color=tty"; type ll; ll'.
Nov 25, 2011 at 12:54
sh -c" the your explanation is applicable for sh too. Am I right?
Nov 25, 2011 at 13:02
sh. Notice that this does work: sh -c $'alias ll="ls -l --color=tty"\ntype ll\nll'
Nov 25, 2011 at 13:10
"watch -x bash -i -c ll"(the "-x" tells watch not to use it's own "sh -c" to execute the given command.) But it successfully runs 'll' once, then backgrounds and stops the process. I don't know why.