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user58029
Asked: 2019-01-02 19:11:40 +0800 CST

AWK: Why $* works inside bash function but not under pipe?

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@terdon in this post answered the related question of mine, but I missed one more question in that post.

Plz refer to the following commands:

calc(){ awk "BEGIN{ print $* }" ;}; calc "((3+(2^3)) * 34^2 / 9)-75.89"

The above commands work fine with calculated result '1337'.

echo '((3+(2^3)) * 34^2 / 9)-75.89' | awk "BEGIN{ print $* }"

But the above commands don't give any result while @terdon explained well about why.

Could you advise what made the first example work with $*?

awk

1 Answers

  1. $* refers to positional parameters - those variables which are referenced by $1 and $2 and so on, and are provided as arguments to scripts and functions. That's the key to your question.

    When you have interactive shell , there's no positional parameters set by default, so $* is empty. You can make it work if you set those via set "((3+(2^3)) * 34^2 / 9)-75.89" command, which will make $1 equal to that string.

    The difference with calc(){ awk "BEGIN{ print $* }" ;}; is that it's a function and functions can process positional parameters (theirs, not the shell's). When you call calc "((3+(2^3)) * 34^2 / 9)-75.89" you're calling a function with positional parameter "((3+(2^3)) * 34^2 / 9)-75.89". There $* won't be empty:

    $ calc(){ echo "Params: '$*'"; awk "BEGIN{ print $* }" ;}; calc "((3+(2^3)) * 34^2 / 9)-75.89"
Params: '((3+(2^3)) * 34^2 / 9)-75.89'
1337
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