awk: calling a function outside of awk

Question

Update:

I'm working on a modular shell script which calls usage() in different level of subprocess. The script sample.sh has the structure resembles below:

sample.sh
├─ ...
├─ usage()
├─ awk
    ├─ usage()
├─ ...

usage() displays brief information on how to use the script (e.g. available arguments and its descriptions). When executed for the first time, usage() is displayed in the beginning of the script. Examples of other conditions for usage() invocation include:

1. awk fails to validate input from stdio or files

2. argument--help is received

3. other user-derived failures are occurred

I'd like to call identical function, usage(), from shell and its direct child process, awk.

---

Original Question:

Function, usage() of sample.sh prints its print statement as desired.

$cat sample.sh
#!/bin/sh
awk '
    BEGIN {
        usage()
    }
    function usage() {
        print "function inside of awk"
    }
'
$./sample.sh
function inside of awk

To take out usage() from awk and put it as a local function in sample.sh~, I tried:

$cat sample.sh~
#!/bin/sh
usage() {
    print "function outside of awk"
}    
awk '
    BEGIN {
        usage()
    }
'
$./sample.sh~
awk: calling undefined function usage
 source line number 3

As we observe, we get the error message saying "undefined function usage" in sample.sh~. How should I improve it?

Answer 1

I find a way to call function out of awk

put below code in a file, such as call it a.sh

$ cat a.sh
usage() {
  print "function outside of awk"
 }

$ chmod +x a.sh

then you can call the function in awk

#!/bin/sh
awk '
    BEGIN {
       system(". a.sh;usage")
    }'

Answer 2

With bash, another option is to export shell functions with export -f, which then become available to awk via the system() call:

#!/usr/bin/env bash

usage() {
  echo "function outside of awk"
}

# Export the usage() function.
export -f usage

awk '
  BEGIN { 
    system("/usr/bin/env bash -c usage") 
  }'

Note that awk invokes sh with system(), which may or may not be bash - if it IS bash (e.g., on OSX), you don't strictly need the /usr/bin/env bash -c portion, but leaving it in should make it work on most platforms (that have bash).