Mini Shell

#!/bin/bash

# If using normal root, avoid changing anything.
if [ -z "$RPM_BUILD_ROOT" -o "$RPM_BUILD_ROOT" = "/" ]; then
  exit 0
fi

exclude_files=""
exclude_files_from=""
exclude_shebangs=""
exclude_shebangs_from=""

usage() {
  local verbose=$1 && shift
  local outfile=$1 && shift
  local status=$1 && shift

  (
    echo 'usage: brp-mangle-shebangs [--files <regexp>] [--files-from <file>] [--shebangs <regexp>] [--shebangs-from <file>]'
    if [ "${verbose}" == "yes" ]; then
      echo '  --files: extended regexp of files to ignore'
      echo '  --files-from: file containing a list of extended regexps of files to ignore'
      echo '  --shebangs: extended regexp of shebangs to ignore'
      echo '  --shebangs-from: file containing a list of extended regexps of shebangs to ignore'
    fi
  ) >>${outfile}
  exit ${status}
}

while [ $# -gt 0 ] ; do
  case "$1" in
    --files)
      exclude_files="${2}"
      shift
      ;;
    --files=*)
      exclude_files="${1##--files=}"
      ;;
    --files-from)
      exclude_files_from="${2}"
      shift
      ;;
    --files-from=*)
      exclude_files_from="${1##--files-from=}"
      ;;
    --shebangs)
      exclude_shebangs="${2}"
      shift
      ;;
    --shebangs=*)
      exclude_shebangs="${1##--shebangs=}"
      ;;
    --shebangs-from)
      exclude_shebangs_from="${2}"
      shift
      ;;
    --shebangs-from=*)
      exclude_shebangs_from="${1##--shebangs-from=}"
      ;;
    --help|--usage|"-?"|-h)
      usage yes /dev/stdout 0
      ;;
    *)
      echo "Unknown option \"${1}\"" 1>&2
      usage no /dev/stderr 1
      ;;
  esac
  shift
done

cd "$RPM_BUILD_ROOT"

# Large packages such as kernel can have thousands of executable files.
# We take care to not fork/exec thousands of "file"s and "grep"s,
# but run just two of them.
# (Take care to exclude filenames which would mangle "file" output).
find -executable -type f ! -path '*:*' ! -path $'*\n*' \
| file -N --mime-type -f - \
| grep -P ".+(?=: text/)" \
| {
fail=0
while IFS= read -r line; do
  f=${line%%:*}

  # Remove the dot
  path="${f#.}"

  if [ -n "$exclude_files" ]; then
    echo "$path" | grep -q -E "$exclude_files" && continue
  fi
  if [ -n "$exclude_files_from" ]; then
    echo "$path" | grep -q -E -f "$exclude_files_from" && continue
  fi


  if ! read shebang_line < "$f"; then
    echo >&2 "*** WARNING: Cannot read the first line from $f, removing executable bit"
    ts=$(stat -c %y "$f")
    chmod -x "$f"
    touch -d "$ts" "$f"
    continue
  fi

  orig_shebang="${shebang_line#\#!}"
  if [ "$orig_shebang" = "$shebang_line" ]; then
    echo >&2 "*** WARNING: $f is executable but has no shebang, removing executable bit"
    ts=$(stat -c %y "$f")
    chmod -x "$f"
    touch -d "$ts" "$f"
    continue
  fi

  # Trim spaces
  while shebang="${orig_shebang//  / }"; [ "$shebang" != "$orig_shebang" ]; do
    orig_shebang="$shebang"
  done
  # Treat "#! /path/to " as "#!/path/to"
  orig_shebang="${orig_shebang# }"

  shebang="$orig_shebang"

  if [ -z "$shebang" ]; then
    echo >&2 "*** WARNING: $f is executable but has empty shebang, removing executable bit"
    ts=$(stat -c %y "$f")
    chmod -x "$f"
    touch -d "$ts" "$f"
    continue
  fi
  if [ -n "${shebang##/*}" ]; then
    echo >&2 "*** ERROR: $f has shebang which doesn't start with '/' ($shebang)"
    fail=1
    continue
  fi

  if ! { echo "$shebang" | grep -q -P "^/(?:usr/)?(?:bin|sbin)/"; }; then
    continue
  fi

  # Replace "special" env shebang:
  # /whatsoever/env /whatever/foo → /whatever/foo
  shebang=$(echo "$shebang" | sed -r -e 's@^(.+)/env /(.+)$@/\2@')
  # /whatsoever/env foo → /whatsoever/foo
  shebang=$(echo "$shebang" | sed -r -e 's@^(.+/)env (.+)$@\1\2@')

  # Replace python3 with the desired Python 3 shebang,
  # if passed as an non-empty environment variable PYTHON3
  if [ -n "${PYTHON3:+x}" ]; then
    shebang=$(echo "$shebang" | sed -r -e "s@/usr/bin/python3(\s|$)@${PYTHON3}\1@")
  fi

  # Replace ambiguous python with python2
  py_shebang=$(echo "$shebang" | sed -r -e 's@/usr/bin/python(\s|$)@/usr/bin/python2\1@')

  if [ "$shebang" != "$py_shebang" ]; then
    echo >&2 "*** ERROR: ambiguous python shebang in $path: #!$orig_shebang. Change it to python3 (or python2) explicitly."
    fail=1
  elif [ "#!$shebang" != "#!$orig_shebang" ]; then
    echo "mangling shebang in $path from $orig_shebang to #!$shebang"
    ts=$(stat -c %y "$f")
    sed -i -e "1c #!$shebang" "$f"
    touch -d "$ts" "$f"
  fi

done

exit $fail
}