shell-command

#!/bin/sh
#
# shell-command: show the current shell command i.e. what shell am I using?
#
# Example:
#
#     shell-command
#     /bin/bash
#
# This script gets the current process id (a.k.a. PID)
# then uses the `ps` command to look up the process id,
# then uses the `sed` command to strip the header row.
#
# This script is useful if you want to know which shell you're using,
# for example if you're using bash shell, zsh shell, fish shell, etc.
#
# ## Comparisons
#
# The $SHELL environment variable is similar but not identical.
# SHELL stores your preferred login shell at the last login time.
# This variable is never modified by your parent or current shell.
#
# Running the `echo $0` command is similar but not identical.
# The `echo $0` typically prints the path of the running program,
# however a program can change its own $0 to something else,
# such as by overriding its own $0 when calling execve(2).
#
# If `echo $0` prints a leading hyphen such as `-bash` then the shell
# was invoked as a login shell; otherwise you are in a non-login shell.
#
# Note that bash will initialise differently depending on it's argv[0].
# If the string starts with a hyphen `-` as in `-bash` then bash will run
# as a login shell; if not then bash will run as an interactive shell.
# Bash can also run as a non-interactive shell (i.e. in a shell script).
#
# Credit:
#
#   * http://unix.stackexchange.com/questions/45458/why-shell-doesnt-change-when-i-run-new-shell
#   * http://unix.stackexchange.com/questions/114058/why-echo-0-gives-different-result-for-two-different-terminals
#
# Version: 1.1.0
# Created: 2016-01-22
# Updated: 2016-01-24
# Contact: Joel Parker Henderson (joel@joelparkerhenderson.com)
# License: GPL
##

ps -p "$$" -o command | sed 1d