我需要一个realpath在OS X上的更换，一个与符号链接和家长参考路径是否正常工作，就像readlink -f会。这包括在解析父引用之前解析路径中的符号链接；例如，如果您已经安装了自制coreutils瓶，则运行：
$ ln -s /var/log/cups /tmp/linkeddir # symlink to another directory
$ greadlink -f /tmp/linkeddir/.. # canonical path of the link parent
/private/var/log
请注意，在解析父目录引用之前readlink -f已解决该问题。当然，在Mac上也没有。/tmp/linkeddir ..readlink -f
因此，作为bash实现的一部分，realpath我在Bash 3.2中重新实现了GNUlib canonicalize_filename_mode(path, CAN_ALL_BUT_LAST)函数调用的功能。这也是GNU readlink -f进行的函数调用：
# shellcheck shell=bash
set -euo pipefail
_contains() {
# return true if first argument is present in the other arguments
local elem value
value="$1"
shift
for elem in "$@"; do
if [[ $elem == "$value" ]]; then
return 0
fi
done
return 1
}
_canonicalize_filename_mode() {
# resolve any symlink targets, GNU readlink -f style
# where every path component except the last should exist and is
# resolved if it is a symlink. This is essentially a re-implementation
# of canonicalize_filename_mode(path, CAN_ALL_BUT_LAST).
# takes the path to canonicalize as first argument
local path result component seen
seen=()
path="$1"
result="/"
if [[ $path != /* ]]; then # add in current working dir if relative
result="$PWD"
fi
while [[ -n $path ]]; do
component="${path%%/*}"
case "$component" in
'') # empty because it started with /
path="${path:1}" ;;
.) # ./ current directory, do nothing
path="${path:1}" ;;
..) # ../ parent directory
if [[ $result != "/" ]]; then # not at the root?
result="${result%/*}" # then remove one element from the path
fi
path="${path:2}" ;;
*)
# add this component to the result, remove from path
if [[ $result != */ ]]; then
result="$result/"
fi
result="$result$component"
path="${path:${#component}}"
# element must exist, unless this is the final component
if [[ $path =~ [^/] && ! -e $result ]]; then
echo "$1: No such file or directory" >&2
return 1
fi
# if the result is a link, prefix it to the path, to continue resolving
if [[ -L $result ]]; then
if _contains "$result" "${seen[@]+"${seen[@]}"}"; then
# we've seen this link before, abort
echo "$1: Too many levels of symbolic links" >&2
return 1
fi
seen+=("$result")
path="$(readlink "$result")$path"
if [[ $path = /* ]]; then
# if the link is absolute, restart the result from /
result="/"
elif [[ $result != "/" ]]; then
# otherwise remove the basename of the link from the result
result="${result%/*}"
fi
elif [[ $path =~ [^/] && ! -d $result ]]; then
# otherwise all but the last element must be a dir
echo "$1: Not a directory" >&2
return 1
fi
;;
esac
done
echo "$result"
}
它包括循环符号链接检测，如果两次（相同）路径相同，则退出。
如果您需要的只是readlink -f，则可以将以上内容用作：
readlink() {
if [[ $1 != -f ]]; then # poor-man's option parsing
# delegate to the standard readlink command
command readlink "$@"
return
fi
local path result seenerr
shift
seenerr=
for path in "$@"; do
# by default readlink suppresses error messages
if ! result=$(_canonicalize_filename_mode "$path" 2>/dev/null); then
seenerr=1
continue
fi
echo "$result"
done
if [[ $seenerr ]]; then
return 1;
fi
}
对于realpath，我还需要--relative-to和--relative-base支持，这将为您提供规范化后的相对路径：
_realpath() {
# GNU realpath replacement for bash 3.2 (OS X)
# accepts --relative-to= and --relative-base options
# and produces canonical (relative or absolute) paths for each
# argument on stdout, errors on stderr, and returns 0 on success
# and 1 if at least 1 path triggered an error.
local relative_to relative_base seenerr path
relative_to=
relative_base=
seenerr=
while [[ $# -gt 0 ]]; do
case $1 in
"--relative-to="*)
relative_to=$(_canonicalize_filename_mode "${1#*=}")
shift 1;;
"--relative-base="*)
relative_base=$(_canonicalize_filename_mode "${1#*=}")
shift 1;;
*)
break;;
esac
done
if [[
-n $relative_to
&& -n $relative_base
&& ${relative_to#${relative_base}/} == "$relative_to"
]]; then
# relative_to is not a subdir of relative_base -> ignore both
relative_to=
relative_base=
elif [[ -z $relative_to && -n $relative_base ]]; then
# if relative_to has not been set but relative_base has, then
# set relative_to from relative_base, simplifies logic later on
relative_to="$relative_base"
fi
for path in "$@"; do
if ! real=$(_canonicalize_filename_mode "$path"); then
seenerr=1
continue
fi
# make path relative if so required
if [[
-n $relative_to
&& ( # path must not be outside relative_base to be made relative
-z $relative_base || ${real#${relative_base}/} != "$real"
)
]]; then
local common_part parentrefs
common_part="$relative_to"
parentrefs=
while [[ ${real#${common_part}/} == "$real" ]]; do
common_part="$(dirname "$common_part")"
parentrefs="..${parentrefs:+/$parentrefs}"
done
if [[ $common_part != "/" ]]; then
real="${parentrefs:+${parentrefs}/}${real#${common_part}/}"
fi
fi
echo "$real"
done
if [[ $seenerr ]]; then
return 1
fi
}
if ! command -v realpath > /dev/null 2>&1; then
# realpath is not available on OSX unless you install the `coreutils` brew
realpath() { _realpath "$@"; }
fi
我在针对此代码的代码审查请求中包含了单元测试。