Project CD (example of making a dual-mode script that can alter the caller's environment)

.proj_dirs

PROJ_DIRS["docs"]="~/library/documents"
PROJ_DIRS["video"]="~/library/videos"
PROJ_DIRS["arduino"]="/home/alw/projects/embedded/Arduino"

__project_dir.sh

#!/bin/bash
# This is not a bash shell script
# But needs to be sourced. However...
# Try:
# eval $(__project_dir.sh --__install project_dir)

if [[ "${BASH_SOURCE[0]}" == "$0" ]]
   then
       if [ "$1" == "--__install" ]   # this should only be called from "real" script
       then
	   aname="$2"
	   if [ "$aname" == "" ]
	   then
	       aname="pcd"    # default alias name
	   fi
	   echo -n "alias '$aname'='source "
	   aname=$(realpath -s "$0")
	   echo "$aname'"
	   exit 0
       fi
       echo "You must source this script"
       exit 1
fi

# Ok your script goes here
# If you call it from your alias
# you can change directories
# set environment variables, etc
# But don't exit! (use return)

# This version uses functions to control variable polution

# this is a simple example
# It maintains an array of project IDs and directories in the CONFIG file
# so for example...
# PROJ_DIRS["docs"]="~/library/documents"
# PROJ_DIRS["video"]="~/library/videos"
# etc...
#
# Then you can switch to a project by tag
# In addition, if the file ./.dir_exit is there
# it will be sourced before you leave and can
# potentially redirect things by setting 
# PROJ_TMP, DIR_NEW and it can examine DIR_OLD
# If the new directory has ./.dir_enter it will also
# be sourced so it can examine the same variables
# You could also set other variables, aliases, etc on entry/exit
#
# Commands:
# eval $(_project_dir.sh --install pcd)   # make alias pcd
# pcd {project}  # change to project directory
# pcd --list     # show all projects
# pcd --add {project} {dir}   # add a project/directory
# (note: last one in the file wins, but old ones are still kept)
# pcd --edit   # edit the config file using $EDITOR

main() {
    local CONFIG=~/.proj_dirs

    if [ "$1" == "--edit" ]   # edit config file
    then
	$EDITOR "$CONFIG"
	return 0
    fi    


    if [ "$1" == "--add" ]  # add a new entry to config
    then
	if [ -z "$2" ] || [ -z "$3" ]
	then
	    echo Usage --add project dir
	    return 1
	fi
	echo "Adding $2"
	echo PROJ_DIRS[\""$2"\"]=\""$3"\" >>"$CONFIG"
	return 0
    fi

    # load project directories
    declare -A PROJ_DIRS     # note that declare makes local variables
    source "$CONFIG"

    if [ "$1" == "--list" ]   # show directories
    then
	local key
	for key in "${!PROJ_DIRS[@]}"
	do
	    echo "$key: ${PROJ_DIRS[$key]}"
	done
	return 0
    fi

# clear out --help or -h so we get default help message
# instead of trying to set project --help
    if [ "$1" == "--help" ] || [ "$1" == "-h" ]
    then
	set --
    fi

    local PROJ_TEMP DIR_NEW
    
    # make sure project exists
    if [ "$1" != "" ]
    then
	if [ "${PROJ_DIRS[$1]}" == "" ]
	then
	    echo "Warning Unknown project $1"
	    PROJ_TEMP=-
	    DIR_NEW="$1"
	else
	    PROJ_TEMP="$1"
	    DIR_NEW="${PROJ_DIRS[$1]}"
	fi
    fi



    # do the switch
    if [ "$1" != "" ]
    then
	local DIR_OLD=$(pwd)    # just in case one of the scripts wants it
	if [ -r ./.dir_exit ]   # note this could set PROJ_TMP or DIR_NEW
	then
	    source ./.dir_exit
	fi
	echo "Setting project $PROJ_TMP"
	cd "$DIR_NEW" || echo change directory failed
	if [ -r ./.dir_enter ]
	then
	    source ./.dir_enter
	fi
	return 0
    fi

# help
    if [ "$1" == "" ]
    then
	'cat' << EOF
A project management script (Al Williams/Hackaday)
You first register it using:    
eval \$(__project_dir.sh --install pcd)   # make alias pcd (or whatever you want)

Commands:
pcd {project}  # change to project directory
pcd --list     # show all projects
pcd --add {project} {dir}   # add a project/directory
     (note: last one in the file wins, but old ones are still kept)
pcd --edit   # edit the config file using $EDITOR
EOF

	return 0    
    fi
}



# Be sure to have this at the end
 __go__() {
    local tmprv
    main "$@"
    tmprv=$?
    unset main, __go__
    return $tmprv
}

__go__ "$@"
return $?