Bash变量管道在别名内不起作用？

Question

I tried creating the following as an alias in my .bash_profile.

alias die_memcached_die="ps -ef | awk '/memcached/ && !/awk/ {print $2}' | xargs kill -9"

It works fine if I run the commands directly on the terminal

ps -ef | awk '/memcached/ && !/awk/ {print $2}' | xargs kill -9

or if I create a bash script to run it.

Just curious why this doesn't work in an alias?

Answer 1

The problem is that you wrap your alias definition in double quotes and so the shell immediately expands $2 and your awk script isn't what you expect it to be.

$ cat aa
alias die_memcached_die="ps -ef | awk '/memcached/ && !/awk/ {print $2}' | xargs kill -9"

echo 'Alias command run is:'
echo 'alias die_memcached_die="ps -ef | awk '\''/memcached/ && !/awk/ {print $2}'\'' | xargs kill -9"'
echo 'Alias actually is:'
alias die_memcached_die

alias die_memcached_die='ps -ef | awk '\''/memcached/ && !/awk/ {print $2}'\'' | xargs kill -9'

echo 'Alias actually is:'
alias die_memcached_die

$ /bin/bash aa
Alias command run is:
alias die_memcached_die="ps -ef | awk '/memcached/ && !/awk/ {print $2}' | xargs kill -9"
Alias actually is:
alias die_memcached_die='ps -ef | awk '\''/memcached/ && !/awk/ {print }'\'' | xargs kill -9'
Alias actually is:
alias die_memcached_die='ps -ef | awk '\''/memcached/ && !/awk/ {print $2}'\'' | xargs kill -9'

That being said both of the comments on the OP about this being a poor alias and a poor idea are correct.

Answer 2

Alias should be enclosed in single quotes to prevent the shell from interpolating variables that are preceded by $ .

You should have your alias like:

alias die_memcached_die='ps -ef | awk "/memcached/ && !/awk/ {print \$2}" | xargs kill -9'

You can have awk definition inside single quotes but then you need to make sure you escape them.

Also, have a look at functions too. They provide better scalability and reliability over aliases.