Get the shell file real path itself when executed or sourced.

self-path-verbose.sh

#!/usr/bin/env bash

echo "---------------- GET SELF PATH ----------------"
echo "NOW \$(pwd) >>> $(pwd)"
ORIGINAL_PWD_GETSELFPATHVAR=$(pwd)

echo "NOW \$0 >>> $0"
echo "NOW \$_ >>>  $_"
echo "NOW \${0##*/} >>> ${0##*/}"

if test -n "$BASH"; then
    echo "RUNNING IN BASH..."
    SH_FILE_RUN_PATH_GETSELFPATHVAR=${BASH_SOURCE[0]}
elif test -n "$ZSH_NAME"; then
    echo "RUNNING IN ZSH..."
    SH_FILE_RUN_PATH_GETSELFPATHVAR=${(%):-%x}
elif test -n "$KSH_VERSION"; then
    echo "RUNNING IN KSH..."
    SH_FILE_RUN_PATH_GETSELFPATHVAR=${.sh.file}
else
    echo "RUNNING IN DASH OR OTHERS ELSE..."
    SH_FILE_RUN_PATH_GETSELFPATHVAR=$(lsof -p $$ -Fn0 | tr -d '\0' | grep "${0##*/}" | tail -1 | sed 's/^[^\/]*//g')
fi

echo "EXECUTING FILE PATH: $SH_FILE_RUN_PATH_GETSELFPATHVAR"

cd "$(dirname "$SH_FILE_RUN_PATH_GETSELFPATHVAR")" || return 1

SH_FILE_RUN_BASENAME_GETSELFPATHVAR=$(basename "$SH_FILE_RUN_PATH_GETSELFPATHVAR")

# Iterate down a (possible) chain of symlinks as lsof of macOS doesn't have -f option.
while [ -L "$SH_FILE_RUN_BASENAME_GETSELFPATHVAR" ]; do
    SH_FILE_REAL_PATH_GETSELFPATHVAR=$(readlink "$SH_FILE_RUN_BASENAME_GETSELFPATHVAR")
    cd "$(dirname "$SH_FILE_REAL_PATH_GETSELFPATHVAR")" || return 1
    SH_FILE_RUN_BASENAME_GETSELFPATHVAR=$(basename "$SH_FILE_REAL_PATH_GETSELFPATHVAR")
done

# Compute the canonicalized name by finding the physical path
# for the directory we're in and appending the target file.
SH_SELF_PATH_DIR_RESULT=$(pwd -P)
SH_FILE_REAL_PATH_GETSELFPATHVAR=$SH_SELF_PATH_DIR_RESULT/$SH_FILE_RUN_BASENAME_GETSELFPATHVAR
echo "EXECUTING REAL PATH: $SH_FILE_REAL_PATH_GETSELFPATHVAR"
echo "EXECUTING FILE DIR: $SH_SELF_PATH_DIR_RESULT"

cd "$ORIGINAL_PWD_GETSELFPATHVAR" || return 1
unset ORIGINAL_PWD_GETSELFPATHVAR
unset SH_FILE_RUN_PATH_GETSELFPATHVAR
unset SH_FILE_RUN_BASENAME_GETSELFPATHVAR
unset SH_FILE_REAL_PATH_GETSELFPATHVAR
echo "---------------- GET SELF PATH ----------------"
# USE $SH_SELF_PATH_DIR_RESULT BEBLOW

self-path.sh

#!/usr/bin/env bash

# ---------------- GET SELF PATH ----------------
ORIGINAL_PWD_GETSELFPATHVAR=$(pwd)
if test -n "$BASH"; then SH_FILE_RUN_PATH_GETSELFPATHVAR=${BASH_SOURCE[0]}
elif test -n "$ZSH_NAME"; then SH_FILE_RUN_PATH_GETSELFPATHVAR=${(%):-%x}
elif test -n "$KSH_VERSION"; then SH_FILE_RUN_PATH_GETSELFPATHVAR=${.sh.file}
else SH_FILE_RUN_PATH_GETSELFPATHVAR=$(lsof -p $$ -Fn0 | tr -d '\0' | grep "${0##*/}" | tail -1 | sed 's/^[^\/]*//g')
fi
cd "$(dirname "$SH_FILE_RUN_PATH_GETSELFPATHVAR")" || return 1
SH_FILE_RUN_BASENAME_GETSELFPATHVAR=$(basename "$SH_FILE_RUN_PATH_GETSELFPATHVAR")
while [ -L "$SH_FILE_RUN_BASENAME_GETSELFPATHVAR" ]; do
    SH_FILE_REAL_PATH_GETSELFPATHVAR=$(readlink "$SH_FILE_RUN_BASENAME_GETSELFPATHVAR")
    cd "$(dirname "$SH_FILE_REAL_PATH_GETSELFPATHVAR")" || return 1
    SH_FILE_RUN_BASENAME_GETSELFPATHVAR=$(basename "$SH_FILE_REAL_PATH_GETSELFPATHVAR")
done
SH_SELF_PATH_DIR_RESULT=$(pwd -P)
SH_FILE_REAL_PATH_GETSELFPATHVAR=$SH_SELF_PATH_DIR_RESULT/$SH_FILE_RUN_BASENAME_GETSELFPATHVAR
cd "$ORIGINAL_PWD_GETSELFPATHVAR" || return 1
unset ORIGINAL_PWD_GETSELFPATHVAR SH_FILE_RUN_PATH_GETSELFPATHVAR SH_FILE_RUN_BASENAME_GETSELFPATHVAR SH_FILE_REAL_PATH_GETSELFPATHVAR
# ---------------- GET SELF PATH ----------------
# USE $SH_SELF_PATH_DIR_RESULT BEBLOW