cx

#!/bin/bash

# changes file permissions depending on the calling file name
# setup: copy this file to the bin/ directory and make hardlinks to it as
# ln cx cw; ln cx cr; ln cx c-w
#
# run as:
# cx filename # makes filename executable
# cw filename # makes filename writable
# cr filename # makes filename readable
# c-w filename # removes w-rights from the filename
#
# see 'cx -h' for the usage help / options
  
# common usage function with the exit at the end
usage() {
  echo "Usage: $sname [options] file [file [file...]]"
  echo '       -a, gives access to all, like a+x, by default +x'
  echo '       -d <directory/path/bin>, path to the bin directory'
  echo "          can be used in 'cx' to copy a new script there"
  echo '       -a, gives access to all, like a+x, by default +x'
  echo '       -d <directory/path/bin>, path to the bin directory'
  echo "          can be used in 'cx' to copy a new script there"
  echo '       -v, verbose mode for chmod'
  echo '       -h, this help message'
  exit 1
}

# whole trick is in this part: getopt validates the input parameters,
# structures them by dividing options and arguments with --,
# and returns them to a variable
# then they are reassigned back to $@ with 'set --'
opts=$(getopt "avhd:" "$@") || usage
set -- $opts

# defining variables' default values
ALL=''
CMD='/usr/bin/chmod'
sname=${0##*/}  # the name this script was called by

# by now we have a well structured $@ which we can trust.
# to go through options one by one we start an endless 'while' loop
# with the nested 'case'. 'shift' makes another trick, every time
# it is invoked it is equal to 'unset $1', thus $@ arguments are
# "shifted down", $2 becomes $1, $3 becomes $2, etc
# 'getopt' adds -- to $@ which separates valid options and the rest
# that did not qualify, when it comes to '--' we 'break' the loop
while true; do
  case ${1} in
    -h) usage ;; # output help message and exit
    -a) ALL=a ;; # if -a is given we set ALL
    -v) CMD+=' -v' ;; # if verbose mode required
    -d) shift # shift to take next item as a directory path for -d
        BINDIR="$1"
        if [[ -z "$BINDIR" || ! -d "$BINDIR" ]]; then
          echo "ERROR: the directory does not exist"
          usage
        fi
     ;;
    --) shift; break ;;   # remove --
  esac
  shift
done


# script body

case "$sname" in
  cx*) $CMD ${ALL}+rx "$@" && \
       [[ -n "$BINDIR" ]] && cp -p $@ $BINDIR ;;
  cw*) $CMD ${ALL}+w "$@" ;;
  cr*) $CMD ${ALL}+r "$@" ;;
  c-w*) $CMD ${ALL}-w "$@" ;;
  *) echo "ERROR: no idea what $sname is supposed to do"; exit 1 ;;
esac