Invoking a script, which has an awk shebang, with

Question

I have an awk script that I have defined thus:

#!/usr/bin/env awk
BEGIN { if (!len) len = 1; end = start + len }
{ for (i = start; i < end; i++) { print $1 } }

I have saved it as columns and chmod +x'd it. I want invoke it so that start and end are defined as it traverses over a file. I was thinking this should work:

cat some_file | columns -v start=2

But it doesn't. Help!

Answer 1

Below is the answer for this problem -

#!/bin/awk -f 

Answer 2

env is the easiest way to handle this problem:

#!/usr/bin/env -S awk -f

to add more options, and to ensure no interference with your arguments, and awk's arguments:

#!/usr/bin/env -S awk -F: -f ${_} --
BEGIN {
    # delete argv[1], which == ENVIRON[_]
    delete ARGV[1]
} # rest of my awk program

as env has a POSIX standard, this shbang should get you around the difficulties of non-standard shbang implementations across unixen.

EDIT

after having written this I realized that '-S' is a non-POSIX compliant FreeBSD env extension. So shell wrapper is probably the way to go, unfortunate as that is.

Answer 3

Try using:

#!/usr/bin/awk -f

as an interpreter

Answer 4

Unfortunately, this is not easy to solve in a portable way. The standard technique looks like this (substitute /usr/bin/awk for your awk path):

#!/usr/bin/awk -f

BEGIN { if (!len) len = 1; end = start + len }
{ for (i = start; i < end; i++) { print $1 } }

The hard-coded awk path and non-standard -f flag, makes this not portable across all *nixes. If you are only ever going to run your script on one machine, then this may work fine. However, to make a portable awk script, you will need to wrap it in a shell script. Here are two ways that you can do it in one file:

The first way is standard and easy to read:

#!/bin/sh

awk '
BEGIN { if (!len) len = 1; end = start + len }
{ for (i = start; i < end; i++) { print $1 } }
' "$@"

Unfortunately, this falls short in two key ways:

1. If your awk script contains a ' character, you will need to type it like this: '"'"' to "escape" it.
2. If you are using a text editor with syntax highlighting, you will not get your awk script properly highlighted.

Another solution, is to use sed to strip out the sh wrapper:

#!/bin/sh
exec awk "$(sed '1,2d' "$0")" "$@"

BEGIN { if (!len) len = 1; end = start + len }
{ for (i = start; i < end; i++) { print $1 } }

This is something like a two line shabang header. It calls awk using the file from line 3 down as the script argument. This allows you to keep your pretty syntax highlighting and you can still use ' characters to your heart's content. The two downsides I see are:

1. Arguably this is non-intuitive to read.
2. If you are using a code linter, it may not like this.