Re: [PATCH] generic/581: remove extra escape character from awk line

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Nov 22, 2023 at 05:03:24PM +0000, Luis Henriques wrote:
> Checking the keys in /proc/key-users is buggy, as there's an extra '\'
> character: in '{print \$4}' the '$4' shouldn't be escaped otherwise the
> 'awk' command will fail.  This has passed unnoticed because the output
> is sent to '_user_do' function and the result assigned to a variable.
> 
> While there, replace 'awk' by $AWK_PROG.
> 
> Signed-off-by: Luis Henriques <lhenriques@suse.de>
> ---
>  tests/generic/581 | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Hi!
> 
> Please note that I'm not an 'awk' expert and I may be wrong!  But if I do
> see an error if I run something like:
> 
> $ awk '/^[[:space:]]*1000:/{print \$4}' /proc/key-users 
> awk: cmd. line:1: /^[[:space:]]*1000:/{print \$4}
> awk: cmd. line:1:                            ^ backslash not last character on line
> 
> But maybe this depends on the awk implementation, although I've tried a few.
> 
> diff --git a/tests/generic/581 b/tests/generic/581
> index cabc7e1c69ab..1a4b571d40ce 100755
> --- a/tests/generic/581
> +++ b/tests/generic/581
> @@ -92,7 +92,7 @@ while grep -E -q '^[0-9a-f]+ [^ ]*i[^ ]*' /proc/keys; do
>  done
>  
>  # Set the user key quota to the fsgqa user's current number of keys plus 5.
> -orig_keys=$(_user_do "awk '/^[[:space:]]*$(id -u fsgqa):/{print \$4}' /proc/key-users | cut -d/ -f1")
> +orig_keys=$(_user_do "$AWK_PROG '/^[[:space:]]*$(id -u fsgqa):/{print $4}' /proc/key-users | cut -d/ -f1")

The backslash is needed to prevent $4 from being expanded by bash, because the
whole pipeline with 'awk' and 'cut' is in a double-quoted string:

    "awk '/^[[:space:]]*$(id -u fsgqa):/{print \$4}' /proc/key-users | cut -d/ -f1"

Without escaping the $, bash would replace $4 with the empty string while it's
doing expansions on the whole double-quoted string.

- Eric