src/dpkg-realpath.sh

   1 #!/bin/sh
   2 #
   3 # Copyright © 2020 Helmut Grohne <helmut@subdivi.de>
   4 # Copyright © 2020 Guillem Jover <guillem@debian.org>
   5 #
   6 # This program is free software; you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation; either version 2 of the License, or
   9 # (at your option) any later version.
  10 #
  11 # This program is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 # GNU General Public License for more details.
  15 #
  16 # You should have received a copy of the GNU General Public License
  17 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
  18
  19 set -e
  20
  21 PROGNAME=$(basename "$0")
  22 version="unknown"
  23 EOL="\n"
  24
  25 PKGDATADIR_DEFAULT=src
  26 PKGDATADIR="${DPKG_DATADIR:-$PKGDATADIR_DEFAULT}"
  27
  28 # shellcheck source=src/sh/dpkg-error.sh
  29 . "$PKGDATADIR/sh/dpkg-error.sh"
  30
  31 show_version()
  32 {
  33   cat <<END
  34 Debian $PROGNAME version $version.
  35
  36 This is free software; see the GNU General Public License version 2 or
  37 later for copying conditions. There is NO warranty.
  38 END
  39 }
  40
  41 show_usage()
  42 {
  43   cat <<END
  44 Usage: $PROGNAME [<option>...] <pathname>
  45
  46 Options:
  47   -z, --zero                   end output line with NUL, not newline.
  48       --instdir <directory>    set the root directory.
  49       --root <directory>       set the root directory.
  50       --version                show the version.
  51   -?, --help                   show this help message.
  52 END
  53 }
  54
  55 canonicalize() {
  56   local src="$1"
  57   local root="$DPKG_ROOT"
  58   local loop=0
  59   local result="$root"
  60   local dst
  61
  62   # Check whether the path is relative and make it absolute otherwise.
  63   if [ "$src" = "${src#/}" ]; then
  64     src="$(pwd)/$src"
  65     src="${src#"$root"}"
  66   fi
  67
  68   # Remove prefixed slashes.
  69   while [ "$src" != "${src#/}" ]; do
  70      src=${src#/}
  71   done
  72   while [ -n "$src" ]; do
  73     # Get the first directory component.
  74     prefix=${src%%/*}
  75     # Remove the first directory component from src.
  76     src=${src#"$prefix"}
  77     # Remove prefixed slashes.
  78     while [ "$src" != "${src#/}" ]; do
  79       src=${src#/}
  80     done
  81     # Resolve the first directory component.
  82     if [ "$prefix" = . ]; then
  83       # Ignore, stay at the same directory.
  84       :
  85     elif [ "$prefix" = .. ]; then
  86       # Go up one directory.
  87       result=${result%/*}
  88       if [ -n "$root" ] && [ "${result#"$root"}" = "$result" ]; then
  89         result="$root"
  90       fi
  91     elif [ -h "$result/$prefix" ]; then
  92       loop=$((loop + 1))
  93       if [ "$loop" -gt 25 ]; then
  94         error "too many levels of symbolic links"
  95       fi
  96       # Resolve the symlink within $result.
  97       dst=$(readlink "$result/$prefix")
  98       case "$dst" in
  99       /*)
 100         # Absolute pathname, reset result back to $root.
 101         result=$root
 102         src="$dst${src:+/$src}"
 103         # Remove prefixed slashes.
 104         while [ "$src" != "${src#/}" ]; do
 105           src=${src#/}
 106         done
 107         ;;
 108       *)
 109         # Relative pathname.
 110         src="$dst${src:+/$src}"
 111         ;;
 112       esac
 113     else
 114       # Otherwise append the prefix.
 115       result="$result/$prefix"
 116     fi
 117   done
 118   # We are done, print the resolved pathname, w/o $root.
 119   result="${result#"$root"}"
 120   printf "%s$EOL" "${result:-/}"
 121 }
 122
 123 setup_colors
 124
 125 DPKG_ROOT="${DPKG_ROOT:-}"
 126 export DPKG_ROOT
 127
 128 while [ $# -ne 0 ]; do
 129   case "$1" in
 130   -z|--zero)
 131     EOL="\0"
 132     ;;
 133   --instdir|--root)
 134     shift
 135     DPKG_ROOT=$1
 136     ;;
 137   --instdir=*)
 138     DPKG_ROOT="${1#--instdir=}"
 139     ;;
 140   --root=*)
 141     DPKG_ROOT="${1#--root=}"
 142     ;;
 143   --version)
 144     show_version
 145     exit 0
 146     ;;
 147   --help|-\?)
 148     show_usage
 149     exit 0
 150     ;;
 151   --)
 152     shift
 153     pathname="$1"
 154     ;;
 155   -*)
 156     badusage "unknown option: $1"
 157     ;;
 158   *)
 159     pathname="$1"
 160     ;;
 161   esac
 162   shift
 163 done
 164
 165 # Normalize root directory.
 166 DPKG_ROOT="${DPKG_ROOT:+$(realpath "$DPKG_ROOT")}"
 167 # Remove default root dir.
 168 if [ "$DPKG_ROOT" = "/" ]; then
 169   DPKG_ROOT=""
 170 fi
 171
 172 [ -n "$pathname" ] || badusage "missing pathname"
 173 if [ "${pathname#"$DPKG_ROOT"}" != "$pathname" ]; then
 174   error "link '$pathname' includes root prefix '$DPKG_ROOT'"
 175 fi
 176
 177 canonicalize "$pathname"
 178
 179 exit 0