Set and use alias within Bash script

Bash scripts by default ignore aliases, unless the command

shopt -s expand_aliases

has been used before the aliased command. This is typically a good thing, as if one has set in ~/.bash_aliases something like

alias mv="mv -v"

any script using mv could produce extremely lengthy and verbose output when installing a program for example.

However, sometimes a user has multiple versions of a program installed in directories in $PATH and for whatever reason cannot use update-alternatives to make the desired one the default. You really should use update-alternatives instead whenever possible as this method described here is not as robust. Because we are not sourceing the Bash script, the alias scope is only within the Bash script itself. That is, once the script is done, the alias disappears.

Let’s say your IT department has installed CMake 2 as /usr/bin/cmake2 and CMake 3 as /usr/bin/cmake3. They really shouldn’t install it like that, but suppose they did anyway. If a script needs CMake 3.x, and you can’t use update-alternatives, do within the Bash script:

shopt -s expand_aliases
alias cmake=/usr/bin/cmake3

Again, we stress this is not general or robust, so only do this as a last resort. You don’t need sudo to use update-alternatives. Put the softlinks under $HOME/.local/bin and put that on your $PATH as a much better choice.

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Written by Michael Hirsch, Ph.D. //

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