Run a Command and then Parameter Substitution in one line

Question

bash# hostname
host1.example.com

I only want host1. So:

SHORT_HOST=$(/bin/hostname)
SHORT_HOST=${SHORT_HOST%%.*}

Can I turn this into a one liner? - or - what is the best way to make $SHORT_HOST readonly, but still get the short hostname?

Answer 1

If you're not limited to just bash's tools, maybe try

SHORT_HOST=$(hostname | sed -e 's/\..*//')

or

SHORT_HOST=$(hostname | cut -d. -f1)

Answer 2

If your environment supports this, you could simply:

typeset -r SHORT_HOST="$(/bin/hostname -s)"

Answer 3

This is just another way using awk command:

/bin/hostname | awk -F'.' '{print $1}'

and if you need to store it in a SHORT_HOST variable use the following:

SHORT_HOST=$(/bin/hostname | awk -F'.' '{print $1}')

Answer 4

In shells other than zsh, you need to perform an intermediate assignment whenever you want to perform multiple transformations on a value.

Of course, there are sometimes workarounds, such as running a command that produces the desired result with no postprocessing or doing the postprocessing via a pipe through an external tool (the pipe solution will be slower and runs into more risk of mangling newlines).

If you want to make the variable read-only, you might find it cleaner to assign to a temporary variable.

tmp=$(/bin/hostname)
typeset -r SHORT_HOST="${tmp%%.*}"

Zsh (but not ksh or bash) supports nested parameter substitutions. There, you can write

typeset -r SHORT_HOST=${$(/bin/hostname)%%.*}