Lib/commands.py

   1 """Execute shell commands via os.popen() and return status, output.
   2
   3 Interface summary:
   4
   5        import commands
   6
   7        outtext = commands.getoutput(cmd)
   8        (exitstatus, outtext) = commands.getstatusoutput(cmd)
   9        outtext = commands.getstatus(file)  # returns output of "ls -ld file"
  10
  11 A trailing newline is removed from the output string.
  12
  13 Encapsulates the basic operation:
  14
  15       pipe = os.popen('{ ' + cmd + '; } 2>&1', 'r')
  16       text = pipe.read()
  17       sts = pipe.close()
  18
  19  [Note:  it would be nice to add functions to interpret the exit status.]
  20 """
  21
  22 # Module 'commands'
  23 #
  24 # Various tools for executing commands and looking at their output and status.
  25 #
  26 # NB This only works (and is only relevant) for UNIX.
  27
  28
  29 # Get 'ls -l' status for an object into a string
  30 #
  31 def getstatus(file):
  32     """Return output of "ls -ld <file>" in a string."""
  33     return getoutput('ls -ld' + mkarg(file))
  34
  35
  36 # Get the output from a shell command into a string.
  37 # The exit status is ignored; a trailing newline is stripped.
  38 # Assume the command will work with '{ ... ; } 2>&1' around it..
  39 #
  40 def getoutput(cmd):
  41     """Return output (stdout or stderr) of executing cmd in a shell."""
  42     return getstatusoutput(cmd)[1]
  43
  44
  45 # Ditto but preserving the exit status.
  46 # Returns a pair (sts, output)
  47 #
  48 def getstatusoutput(cmd):
  49     """Return (status, output) of executing cmd in a shell."""
  50     import os
  51     pipe = os.popen('{ ' + cmd + '; } 2>&1', 'r')
  52     text = pipe.read()
  53     sts = pipe.close()
  54     if sts == None: sts = 0
  55     if text[-1:] == '\n': text = text[:-1]
  56     return sts, text
  57
  58
  59 # Make command argument from directory and pathname (prefix space, add quotes).
  60 #
  61 def mk2arg(head, x):
  62     import os
  63     return mkarg(os.path.join(head, x))
  64
  65
  66 # Make a shell command argument from a string.
  67 # Return a string beginning with a space followed by a shell-quoted
  68 # version of the argument.
  69 # Two strategies: enclose in single quotes if it contains none;
  70 # otherwise, enclose in double quotes and prefix quotable characters
  71 # with backslash.
  72 #
  73 def mkarg(x):
  74     if '\'' not in x:
  75         return ' \'' + x + '\''
  76     s = ' "'
  77     for c in x:
  78         if c in '\\$"`':
  79             s = s + '\\'
  80         s = s + c
  81     s = s + '"'
  82     return s