Optional parameters in bash function

Question

I have a function for quickly making a new SVN branch which looks like so

function svcp() { svn copy "repoaddress/branch/$1.0.x" "repoaddress/branch/dev/$2" -m "dev branch for $2"; } 

Which I use to quickly make a new branch without having to look up and copy paste the addresses and some other stuff. However for the message (-m option), I'd like to have it so that if I provide a third parameter then that is used as the message, otherwise the 'default' message of "dev branch for $2" is used. Can someone explain how this is done?

Answer 1

function svcp() { msg=${3:-dev branch for $2} svn copy "repoaddress/branch/$1.0.x" "repoaddress/branch/dev/$2" -m "$msg"; } 

the variable msg is set to $3 if $3 is non-empty, otherwise it is set to the default value of dev branch for $2. $msg is then used as the argument for -m.

Answer 2

from the bash man page:

 ${parameter:-word} Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted. 

in your case, you would use

 $ function svcp() { def_msg="dev branch for $2" echo svn copy "repoaddress/branch/$1.0.x" "repoaddress/branch/dev/$2" -m \"${3:-$def_msg}\"; } $ svcp 2 exciting_new_stuff svn copy repoaddress/branch/2.0.x repoaddress/branch/dev/exciting_new_stuff -m "dev branch for exciting_new_stuff" $ svcp 2 exciting_new_stuff "secret recipe for world domination" svn copy repoaddress/branch/2.0.x repoaddress/branch/dev/exciting_new_stuff -m "secret recipe for world domination" $ 

you can remove the echo command if you are satisfied with the svn commands that are generated