/usr/bin/gsl-config is in libgsl-dev 2.4+dfsg-6.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80  | #! /bin/sh
prefix=/usr
exec_prefix=/usr
includedir=/usr/include
usage()
{
    cat <<EOF
Usage: gsl-config [OPTION]
Known values for OPTION are:
  --prefix		show GSL installation prefix 
  --libs		print library linking information, with cblas
  --libs-without-cblas	print library linking information, without cblas
  --cflags		print pre-processor and compiler flags
  --help		display this help and exit
  --version		output version information
An external CBLAS library can be specified using the GSL_CBLAS_LIB
environment variable. The GSL CBLAS library is used by default.
EOF
    exit $1
}
if test $# -eq 0; then
    usage 1
fi
cflags=false
libs=false
while test $# -gt 0; do
    case "$1" in
    -*=*) optarg=`echo "$1" | sed 's/[-_a-zA-Z0-9]*=//'` ;;
    *) optarg= ;;
    esac
    case "$1" in
    --prefix=*)
	prefix=$optarg
	;;
    --prefix)
	echo $prefix
	;;
    --version)
	echo 2.4
	exit 0
	;;
    --help)
	usage 0
	;;
    --cflags)
       	echo -I/usr/include 
       	;;
    --libs)
        : ${GSL_CBLAS_LIB=-lgslcblas}
	echo -L/usr/lib/x86_64-linux-gnu -lgsl $GSL_CBLAS_LIB -lm
       	;;
    --libs-without-cblas)
	echo -L/usr/lib/x86_64-linux-gnu -lgsl -lm
       	;;
    *)
	usage
	exit 1
	;;
    esac
    shift
done
exit 0
 |