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Showing content from https://unix.stackexchange.com/questions/4023/bash-functions-vs-scripts below:

bash - Aliases vs functions vs scripts

The main difference between aliases and functions is that aliases don't take arguments¹, but functions do. When you write something like alias l='ls --color', l foo is expanded to ls --color foo; you can't grab foo into the alias expansion and do something different with it the way you can do with a function. See also How to pass parameter to alias?.

Aliases are looked up before functions: if you have both a function and an alias called foo, foo invokes the alias. (If the alias foo is being expanded, it's temporarily blocked, which makes things like alias ls='ls --color' work. Also, you can bypass an alias at any time by running \foo.) I wouldn't expect to see a measurable performance difference though.

Functions and standalone scripts have mostly similar capabilities; here are a few differences I can think of:

• A function runs inside the shell environment; a script runs in a separate process. Therefore a function can change the shell environment: define environment variables, change the current directory, etc. A standalone script can't do that.
• A function must be written in the language of the shell you want to use it in. A script can be written in any language.
• Functions are loaded when they are defined. Scripts are loaded each time they are invoked. This has several consequences:
  • If you modify a script, you get the new version the next time you invoke it. If you change a function's definition, you have to reload the definition.
  • Functions are faster on heavily loaded systems.
  • If you have a lot of functions that you may not use, they'll take up memory. Ksh and zsh, but I think not bash, have a form of function autoloading.

Something that's intermediate between a function and a standalone script is a script snippet that you read with the source or . builtin. Like a function, it can modify the shell's environment, and must be written in the shell's language. Like a script, it is loaded each time it's invoked and no sooner.

¹ _{Yeah, I know, this doesn't apply to tcsh.}

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