include library of functions in awk

With GNU awk:

$ ls lib
prims.awk

$ cat lib/prims.awk
function abs(num) { return (num > 0 ? num : -num) }
function max(a,b) { return (a > b ? a : b) }
function min(a,b) { return (a < b ? a : b) }

$ export AWKPATH="$PWD/lib"

$ awk -i prims.awk 'BEGIN{print min(4,7), abs(-3)}'
4 3

$ cat tst.awk
@include "prims.awk"
BEGIN { print min(4,7), abs(-3) }

$ awk -f tst.awk
4 3

You can have multiple -f program-file options, so one can be your common functions and the other can be a specific problem solving awk script, which will have access to those functions.

awk -f common-funcs.awk -f specific.awk file-to-process.txt

I don't know if this is what you were looking for, but it's the best I've come up with. Here's an example:

$ cat common_func.awk
# Remove spaces from front and back of string
function trim(s) {
  gsub(/^[ \t]+/, "", s);
  gsub(/[ \t]+$/, "", s);
  return s;
}

$ cat specific.awk
{ print $1, $2 }
{ print trim($1), trim($2) }

$ cat file-to-process.txt 
abc    |    def   |

2$ awk -F\| -f common_func.awk -f specific.awk file-to-process.txt 
abc         def   
abc def

With regular awk (non-gnu) you can't mix the -f program-file option with an inline program. That is, the following won't work:

awk -f common_func.awk '{ print trim($1) }' file-to-process.txt # WRONG 

As pointed out in the comments, however, with gawk you can use the -f option together with -e:

awk -f file.awk -e '{stuff}' file.txt

In case if you can't use -i (if your awk < 4.1 version ), which EdMorton suggested, make a try of below works with GNU Awk 3.1.7

--source program-text

Provide program source code in the program-text. This option allows you to mix source code in files with source code that you enter on the command line. This is particularly useful when you have library functions that you want to use from your command-line programs

$ awk --version
GNU Awk 3.1.7
Copyright (C) 1989, 1991-2009 Free Software Foundation.

$ cat primes.awk 
function abs(num) { return (num > 0 ? num : -num) }
function max(a,b) { return (a > b ? a : b) }
function min(a,b) { return (a < b ? a : b) }

$ awk -f primes.awk --source 'BEGIN{print min(4,7), abs(-3)}'
4 3