source: vendor/bash/3.1-p17/examples/scripts.v2/where

#! /bin/bash
#
# original from:
# @(#) where.ksh 1.1 94/07/11
# 91/01/12 john h. dubois iii (john@armory.com)
# 92/08/10 Only print executable *files*.
# 92/10/06 Print err msg if no match found.
# 92/11/27 Added implicit *
# 93/07/23 Print help only if -h is given.
# 94/01/01 Added -x option
# 94/07/11 Don't bother with eval
#
# conversion to bash v2 syntax done by Chet Ramey

name=${0##*/}
Usage="Usage: $name [-hx] 'pattern' ..."
typeset -i exact=0

phelp()
{
echo "$name: find executable files in PATH that match patterns.
$Usage
$name searches each directory specified in the PATH environment variable
for executable files that match the specified patterns.  Patterns are
given as Korn shell filename patterns.  They are surrounded by implicit
'*' characters, so that \"foo\" will match any executble file whose name
contains contains \"foo\".  This can be overridden by using '^' and '$' to
force a match to start at the beginning and end at the end of a filename
respectively.  Characters that are special to the shell must generally
be protected from the shell by surrounding them with quotes.
Examples:
$name foo
lists all executable files in PATH that contain foo.
$name '^b*sh$'
lists all executable files in PATH that start with b and end with sh.
An error message is printed if a no matching file is found for a pattern.
Options:
-h: Print this help.
-x: Find exact matches only; equivalent to putting ^ and $ at the start
    and end of each pattern."
}

istrue()
{
        test 0 -ne "$1"
}

isfalse()
{
        test 0 -eq "$1"
}

while getopts "xh" opt; do
        case "$opt" in
        x)      exact=1;;
        h)      phelp ; exit 0;;
        *)      echo -e "$Usage\nUse -h for help." 1>&2; exit 2;;
        esac
done

shift $((OPTIND-1))

set +f                  # make sure filename globbing is on
Args=("$@")             # save args

OIFS=$IFS
IFS=:           # Make PATH be split on :
Paths=($PATH)
IFS=$OIFS

for arg in "${Args[@]}"; do

    # get rid of leading ^
    if istrue $exact; then
        arg=${arg}
    else
            case "$arg" in
            ^*) arg=${arg#?};;
            *) arg="*$arg" ;;   # Pattern is not anchored at start
            esac
    fi

    # get rid of trailing $
    if istrue $exact; then
        arg="$arg"
    else
        case "$arg" in
        *\$)    arg=${arg%?} ;;
        *)      arg="$arg*" ;;
        esac
    fi

    found=0     # Pattern not found yet
    Patterns=
    # Make a pattern for each element of PATH
    for PathElem in "${Paths[@]}"; do
        [ -z "$PathElem" ] && PathElem=.
        Patterns="$Patterns $PathElem/$arg"
    done

    # Find all pattern matches that are executable regular files.
    for file in $Patterns; do
        if [ -x "$file" ] && [ -f "$file" ]; then
            echo "$file"
            found=1
        fi
    done
    if [ $found = 0 ]; then
        echo "$arg: not found." 1>&2
    fi
done