56 lines
2.7 KiB
Text
56 lines
2.7 KiB
Text
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#!/bin/sh
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# Function by mklement0
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# https://stackoverflow.com/a/29835459/5309963
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# The following, POSIX-compliant shell function implements what
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# GNU's readlink -e does and is a reasonably robust solution
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# that only fails in two rare edge cases:
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# - paths with embedded newlines (very rare)
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# - filenames containing literal string -> (also rare)
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( # Execute the function in a *subshell* to localize variables and the effect of `cd`.
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target=$1 fname= targetDir= CDPATH=
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# Try to make the execution environment as predictable as possible:
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# All commands below are invoked via `command`, so we must make sure that `command`
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# itself is not redefined as an alias or shell function.
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# (Note that command is too inconsistent across shells, so we don't use it.)
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# `command` is a *builtin* in bash, dash, ksh, zsh, and some platforms do not even have
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# an external utility version of it (e.g, Ubuntu).
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# `command` bypasses aliases and shell functions and also finds builtins
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# in bash, dash, and ksh. In zsh, option POSIX_BUILTINS must be turned on for that
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# to happen.
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{ \unalias command; \unset -f command; } >/dev/null 2>&1
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[ -n "$ZSH_VERSION" ] && options[POSIX_BUILTINS]=on # make zsh find *builtins* with `command` too.
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while :; do # Resolve potential symlinks until the ultimate target is found.
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[ -L "$target" ] || [ -e "$target" ] || { command printf '%s\n' "ERROR: '$target' does not exist." >&2; return 1; }
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command cd "$(command dirname -- "$target")" # Change to target dir; necessary for correct resolution of target path.
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fname=$(command basename -- "$target") # Extract filename.
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[ "$fname" = '/' ] && fname='' # !! curiously, `basename /` returns '/'
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if [ -L "$fname" ]; then
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# Extract [next] target path, which may be defined
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# *relative* to the symlink's own directory.
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# Note: We parse `ls -l` output to find the symlink target
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# which is the only POSIX-compliant, albeit somewhat fragile, way.
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target=$(command ls -l "$fname")
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target=${target#* -> }
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continue # Resolve [next] symlink target.
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fi
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break # Ultimate target reached.
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done
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targetDir=$(command pwd -P) # Get canonical dir. path
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# Output the ultimate target's canonical path.
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# Note that we manually resolve paths ending in /. and /.. to make sure we have a normalized path.
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if [ "$fname" = '.' ]; then
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command printf '%s\n' "${targetDir%/}"
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elif [ "$fname" = '..' ]; then
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# Caveat: something like /var/.. will resolve to /private (assuming /var@ -> /private/var), i.e. the '..' is applied
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# AFTER canonicalization.
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command printf '%s\n' "$(command dirname -- "${targetDir}")"
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else
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command printf '%s\n' "${targetDir%/}/$fname"
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fi
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)
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