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Getting Absolute Paths of UNIX Directories and Filenames in Shell Scripts

Posted 07-08-2011 at 03:05 AM by konsolebox
Updated 07-17-2011 at 09:11 AM by konsolebox

This post is a compilation of the function getabspath() for different shells that can be used to get the absolute form of a path. The function accepts an argument path then returns the absolute form of it to the variable $__.

bash (3.0 and newer only)

Code:

function getabspath {
	local -a T1 T2
	local -i I=0
	local IFS=/ A

	case "$1" in
	/*)
		read -r -a T1 <<< "$1"
		;;
	*)
		read -r -a T1 <<< "/$PWD/$1"
		;;
	esac

	T2=()

	for A in "${T1[@]}"; do
		case "$A" in
		..)
			[[ I -ne 0 ]] && unset T2\[--I\]
			continue
			;;
		.|'')
			continue
			;;
		esac

		T2[I++]=$A
	done

	case "$1" in
	*/)
		[[ I -ne 0 ]] && __="/${T2[*]}/" || __=/
		;;
	*)
		[[ I -ne 0 ]] && __="/${T2[*]}" || __=/.
		;;
	esac
}

bash (2.05b and newer only)

Code:

function getabspath {
	local -a T=()
	local -i I=0
	local IFS=/ A

	case "$1" in
	/*)
		__=$1
		;;
	*)
		__=/$PWD/$1
		;;
	esac

	while read -r -d / A; do
		case "$A" in
		..)
			[[ I -ne 0 ]] && unset T\[--I\]
			continue
			;;
		.|'')
			continue
			;;
		esac

		T[I++]=$A
	done <<< "$__/"

	case "$1" in
	*/)
		[[ I -ne 0 ]] && __="/${T[*]}/" || __=/
		;;
	*)
		[[ I -ne 0 ]] && __="/${T[*]}" || __=/.
		;;
	esac
}

bash (all stable versions)

Code:

function getabspath {
	local -a T=()
	local -i I=0
	local IFS=/ A

	case "$1" in
	/*)
		__=$1
		;;
	*)
		__=/$PWD/$1
		;;
	esac

	while read -r -d / A; do
		case "$A" in
		..)
			[[ I -ne 0 ]] && unset T\[--I\]
			continue
			;;
		.|'')
			continue
			;;
		esac

		T[I++]=$A
	done << .
$__/
.

	case "$1" in
	*/)
		[[ I -ne 0 ]] && __="/${T[*]}/" || __=/
		;;
	*)
		[[ I -ne 0 ]] && __="/${T[*]}" || __=/.
		;;
	esac
}

ksh (original)

Code:

if
	__=.
	read __ <<< "$__"
	[[ $__ = '"."' ]]
then
	function getabspath {
		typeset T1 T2
		typeset -i I=0
		typeset IFS=/ A

		case "$1" in
		/*)
			read -r -A T1 <<< $1
			;;
		*)
			read -r -A T1 <<< $PWD/$1
			;;
		esac

		set -A T2

		for A in "${T1[@]}"; do
			case "$A" in
			..)
				[[ I -ne 0 ]] && unset T2\[--I\]
				continue
				;;
			.|'')
				continue
				;;
			esac

			T2[I++]=$A
		done

		case "$1" in
		*/)
			[[ I -ne 0 ]] && __="/${T2[*]}/" || __=/
			;;
		*)
			[[ I -ne 0 ]] && __="/${T2[*]}" || __=/.
			;;
		esac
	}
else
	function getabspath {
		typeset T1 T2
		typeset -i I=0
		typeset IFS=/ A

		case "$1" in
		/*)
			read -r -A T1 <<< "$1"
			;;
		*)
			read -r -A T1 <<< "$PWD/$1"
			;;
		esac

		set -A T2

		for A in "${T1[@]}"; do
			case "$A" in
			..)
				[[ I -ne 0 ]] && unset T2\[--I\]
				continue
				;;
			.|'')
				continue
				;;
			esac

			T2[I++]=$A
		done

		case "$1" in
		*/)
			[[ I -ne 0 ]] && __="/${T2[*]}/" || __=/
			;;
		*)
			[[ I -ne 0 ]] && __="/${T2[*]}" || __=/.
			;;
		esac
	}
fi

pdksh

Code:

getabspath() {
	typeset A T IFS=/ TOKENS I=0 J=0

	A=${1%/}

	if [[ -n $A ]]; then
		while :; do
			T=${A%%/*}

			case "$T" in
			..)
				if [[ I -gt 0 ]]; then
					unset TOKENS\[--I\]
				else
					(( ++J ))
				fi
				;;
			.|'')
				;;
			*)
				TOKENS[I++]=$T
				;;
			esac

			case "$A" in
			*/*)
				A=${A#*/}
				;;
			*)
				break
				;;
			esac
		done
	fi

	__="/${TOKENS[*]}"

	if [[ $1 != /* ]]; then
		A=${PWD%/}

		while [[ J -gt 0 && -n $A ]]; do
			A=${A%/*}
			(( --J ))
		done

		[[ -n $A ]] && __=$A${__%/}
	fi

	if [[ $__ = / ]]; then
		[[ $1 != */ ]] && __=/.
	elif [[ $1 == */ ]]; then
		__=$__/
	fi
}

zsh

Code:

function getabspath {
	local -a TOKENS; set -A TOKENS
	local -i I=0
	local IFS=/ T

	__=$1

	case "$1" in
	/*)
		set -- ${=1}
		;;
	*)
		set -- ${=PWD} ${=1}
		;;
	esac

	for T; do
		case "$T" in
		..)
			[[ I -ne 0 ]] && TOKENS[I--]=()
			continue
			;;
		.|'')
			continue
			;;
		esac

		TOKENS[++I]=$T
	done

	case "$__" in
	*/)
		[[ I -ne 0 ]] && __="/${TOKENS[*]}/" || __=/
		;;
	*)
		[[ I -ne 0 ]] && __="/${TOKENS[*]}" || __=/.
		;;
	esac
}

any other shell based from the original sh

Code:

# first version - assuming the script doesn't mind 'set -f' being set

getabspath() {
	case "$1" in
	/*)
		__=$1
		;;
	*)
		__=`exec pwd`/$1
		;;
	esac

	set -f
	IFS=/
	set -- $__

	while :; do
		__='' __L=''

		for __A; do
			shift

			case "$__A" in
			..)
				[ -z "$__L" ] && continue
				shift "$#"
				set -- $__ "$@"
				continue 2
				;;
			.|'')
				continue
				;;
			esac

			[ -n "$__L" ] && __=$__/$__L
			__L=$__A
		done

		__=$__/$__L

		break
	done

	unset __A __L

	case "$1" in
	*/)
		[ ! "$__" = / ] && __=$__/
		;;
	*)
		[ "$__" = / ] && __=/.
		;;
	esac
}

# 2nd version - encapsulates settings inside a subshell

getabspath() {
	case "$1" in
	/*)
		__=$1
		;;
	*)
		__=`exec pwd`/$1
		;;
	esac

	__=`
		set -f
		IFS=/
		set -- $__

		while :; do
			__='' L=''

			for A; do
				shift

				case "$A" in
				..)
					[ -z "$L" ] && continue
					shift "$#"
					set -- $__ "$@"
					continue 2
					;;
				.|'')
					continue
					;;
				esac

				[ -n "$L" ] && __=$__/$L
				L=$A
			done

			__=$__/$L

			break
		done

		echo "$__"
	`

	case "$1" in
	*/)
		[ ! "$__" = / ] && __=$__/
		;;
	*)
		[ "$__" = / ] && __=/.
		;;
	esac
}

# 3rd version - try to make things run faster; prevent it from reparsing commands

getabspath() {
	case "$1" in
	/*)
		__=$1
		;;
	*)
		__=`exec pwd`/$1
		;;
	esac

	__=`getabspath_`

	case "$1" in
	*/)
		[ ! "$__" = / ] && __=$__/
		;;
	*)
		[ "$__" = / ] && __=/.
		;;
	esac
}

getabspath_() {
	set -f
	IFS=/
	set -- $__

	while :; do
		__='' L=''

		for A; do
			shift

			case "$A" in
			..)
				[ -z "$L" ] && continue
				shift "$#"
				set -- $__ "$@"
				continue 2
				;;
			.|'')
				continue
				;;
			esac

			[ -n "$L" ] && __=$__/$L
			L=$A
		done

		__=$__/$L

		break
	done

	echo "$__"
}

# 4th version - just using awk (some shells doesn't work with the ones above)

getabspath() {
	__=`
		awk -- '
			BEGIN {
				PATH = ARGV[1]

				if (ARGV[1] !~ "^[/]")
					PATH = ARGV[2] "/" PATH

				FS = "/"
				$0 = PATH

				T = 0

				for (F = 1; F <= NF; F++) {
					if ($F == "." || $F == "") {
						continue
					} else if ($F == "..") {
						if (T)
							--T
					} else {
						TOKENS[T++]=$F
					}
				}

				if (T) {
					for (I = 0; I < T; I++)
						ABS = ABS "/" TOKENS[I]
					if (PATH ~ /\/$/)
						ABS = ABS "/"
				} else if (PATH ~ /\/$/) {
					ABS = "/"
				} else {
					ABS = "/."
				}

				print ABS

				exit
			}
		' "$1" "`exec pwd`"
	`
}

Getting Absolute Paths of UNIX Directories and Filenames in Shell Scripts

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