#!/bin/bash
# filelock--A flexible file locking mechanism

setglobal retries = '"10'"            # Default number of retries
setglobal action = '"lock'"           # Default action
setglobal nullcmd = $[which true]     # Null command for lockfile

while getopts "lur:" opt {
  match $opt {
    with l  setglobal action = '"lock'"      
    with u  setglobal action = '"unlock'"    
    with r  setglobal retries = $OPTARG  
  }
}
shift $shExpr('$OPTIND - 1')

if test $Argc -eq 0  { # Output a multi-line error message to stdout.
  cat << """ >&2
Usage: $0 [-l|-u] [-r retries] LOCKFILE
Where -l requests a lock (the default), -u requests an unlock, -r X 
specifies a max number of retries before it fails (default = $retries).
"""
> !2
Usage: $0 [-l|-u] [-r retries] LOCKFILE
Where -l requests a lock (the default), -u requests an unlock, -r X 
specifies a max number of retries before it fails (default = $retries).
EOF
  exit 1
}

# Ascertain if we have the lockfile command.

if test -z $[which lockfile | grep -v '^no ]  {
  echo "$0 failed: 'lockfile' utility not found in PATH." > !2
  exit 1
}
if test $action = "lock"  {
  if ! lockfile -1 -r $retries $1 !2 > /dev/null {
    echo "$0: Failed: Couldn't create lockfile in time" > !2
    exit 1
  }
} else {    # Action = unlock.
  if test ! -f $1  {
    echo "$0: Warning: lockfile $1 doesn't exist to unlock" > !2
    exit 1
  }
  rm -f $1
}

exit 0