BEGIN: command not found in a bare simple awk script when run via sourcing

Question

I'm learning awk today, but I cannot succeed in having the most simple scripts to work.

#!/usr/bin/env -S awk -f
BEGIN { }
{ }
END { }

this outputs BEGIN: command not found

or even

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

this outputs {}: command not found

When I launch $ /usr/bin/env -S awk -f , I do have the awk executable that display its default output.

And $ awk --version says it's awk version 5.0.1 , on nixos 19.09.

I need to use /usr/bin/env, because nixos files are not following the traditionnal FHS directory hierarchy.

I suspect I'm missing something obvious but looking awk tutorials and SO questions has not given me any clue for now.

EDIT: the command line I use to launch the script

ls -l | . testawk.sh

Answer 1

Sourcing is not the same as executing. Specifically, sourcing expects a list of commands that can be executed in the current shell. The following is from bash's help .:

.: . filename [arguments]

Execute commands from a file in the current shell.

Read and execute commands from FILENAME in the current shell. The entries in $PATH are used to find the directory containing FILENAME. If any ARGUMENTS are supplied, they become the positional parameters when FILENAME is executed.

So, when you run . file, your shell will read the file and execute each command it finds. However, this means that the shebang line is ignored and treated like a regular comment. Therefore, your shell and not awk, was attempting to execute BEGIN.

To avoid this, you should execute the script instead of sourcing it. If, for some reason, you just have to source it, write an awk command in the script:

awk '
BEGIN { }
{ }
END { }'

Then, you can do

ls | . ./a.awk 

Although I can't really think of why you would ever want to.

---

As an aside, you should be aware that . (or source, in bash) looks for file names in your $PATH by default. So, if you run . foo, and have a foo file in the current directory and a foo file in any directory in your $PATH, then the file that will be sourced is the one in your $PATH and not the one in your current directory. To avoid this, always use full paths when sourcing: . ./foo.

Answer 2

As mentionned in the comments by AdminBee, the script was called in a wrong manner (sourcing the content).

The correct way is:

ls -l | ./test.awk

Or also, more simply, without relying on the #! line:

ls -l | awk -f ./test.awk

Answer 3

Never use a shebang to call awk as that robs you of the ability to separate your script arguments into parts that should be done in shell vs parts that should be done in awk and to separate awk arguments from awk variable assignments. Just write your script as:

#!/usr/bin/env bash

/usr/bin/env awk '
BEGIN { }
{ }
END { }
' "$@"

There will be times when you want to modify it to do things like set awk variables:

#!/usr/bin/env bash

rs="$1"
fs="$2"
shift 2

/usr/bin/env awk -v RS="$rs" -F "$fs" '
BEGIN { }
{ }
END { }
' "$@"

which should be trivial like the above but you can't do if you're invoking awk with a shebang.