Bash – How to save a function in bash for later use

bashfunction

I have this function to get MAC address from IP:

ip2arp()  {
   local ip="$1"
   ping -c1 -w1 "$ip" >/dev/null
   arp -n "$ip" | awk '$1==ip {print $3}' ip="$ip"
   }

What is the right way for using it later? Save to /usr/bin as sh and make it executable, or save it in a home directory and make an alias in bash? Is there a right and wrong way?

Best Answer

If it's only for your personal use then you could add it to your shell's initialization file as a function, e.g. ~/.bashrc.

For a summary of the different initialization files in Bash you can consult the Bash Guide for Beginners:

Bash Guide for Beginners - Section 3.1: Shell Initialization Files

Also see the Bash Reference Manual:

Bash Reference Manual - Section 6.2: Bash Startup Files

A typical pattern would be to put your function definition in your ~/.bashrc file and source that file from your ~/.bash_profile.

But it's probably worth noting that which profile file to use can depend on your OS, your terminal application, and your own preferences. See for example the following posts on AskDifferent:

Also see this post on StackOverflow:

What's the difference between .bashrc, .bash_profile, and .environment?

Alternatively, you can create a personal directory for your own scripts (e.g. I use ~/local/bin) and then add that directory to your PATH in your profile file (i.e. export PATH="${HOME}/local/bin:${PATH}).

If you want to make it available to other users then you might put it in /usr/local/bin as a script (rather than /usr/bin).

For further discussion regarding where to put executable files, see the following posts:

Related Solutions

Bash – automatically load shell scripts from /usr/bin

The alias you have defined will only take effect once the alias command is actually called. Thus if you were to do this:

$ source myscript
$ e "Hello"

It should work. However, this is clearly not ideal since you want e to be available whenever you start bash. Luckily, bash provides a number of ways to automatically run commands when the shell is started. For the full details of how bash starts up, see the manual page. For our purposes, it is enough to know that ~/.bashrc (that is, a file named ".bashrc" in your home directory) is run as your shell starts up. One way to make your alias available at startup would be to add this line at the end of ~/.bashrc:

source myscript

However, if you were to do this for every alias you wanted, your /usr/bin folder would likely become a mess. And, if you are on a multi-user system, filling /usr/bin/ with scripts like this may cause other users problems as well. Thus, it is better to place your aliases right inside .bashrc and forgo the separate script all together. Since you are using Ubuntu, inside your .bashrc file you probably have something that looks like this:

if [ -f ~/.bash_aliases ]; then
. ~/.bash_aliases 
fi

This code looks for a file call .bash_aliases in your home directory and runs anything it finds in that file as well. If you have this, or if you add this code to your .bashrc, you could also put your alias in ~/.bash_aliases. This provides an easy way to keep all your aliases in one place and keep your .bashrc file uncluttered.

Shell – How to use a bash function like a regular command in a pipe chain

In your function definition, I would suggest replacing:

echo "cat $1 | pv -w 20 -s ${__size}"

with just:

cat $1 | pv -w 20 -s ${__size}

This way, the function itself will execute this bit of code, without requiring a call to eval in the caller.

Best Answer

Related Solutions

Bash – automatically load shell scripts from /usr/bin

Shell – How to use a bash function like a regular command in a pipe chain

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