How can I tell if my script is being run from a cronjob or from the command line?

Question

I have a script and it's display show's upload progress by writing to the same console line. When the script is run from a cron job, rather than writing to a single line, I get many lines:

***   E0710091001.DAT  ***   [0.67%]
***   E0710091001.DAT  ***   [1.33%]
***   E0710091001.DAT  ***   [2.00%]
***   E0710091001.DAT  ***   [2.66%]
***   E0710091001.DAT  ***   [3.33%]
***   E0710091001.DAT  ***   [3.99%]
***   E0710091001.DAT  ***   [4.66%]
***   E0710091001.DAT  ***   [5.32%]
***   E0710091001.DAT  ***   [5.99%]
***   E0710091001.DAT  ***   [6.65%]
***   E0710091001.DAT  ***   [7.32%]
***   E0710091001.DAT  ***   [7.98%]
***   E0710091001.DAT  ***   [8.65%]
***   E0710091001.DAT  ***   [9.32%]
***   E0710091001.DAT  ***   [9.98%]
***   E0710091001.DAT  ***   [10.65%]
***   E0710091001.DAT  ***   [11.31%]
***   E0710091001.DAT  ***   [11.98%]
***   E0710091001.DAT  ***   [12.64%]
***   E0710091001.DAT  ***   [13.31%]
***   E0710091001.DAT  ***   [13.97%]
***   E0710091001.DAT  ***   [14.64%]
***   E0710091001.DAT  ***   [15.30%]
***   E0710091001.DAT  ***   [15.97%]
***   E0710091001.DAT  ***   [16.63%]
***   E0710091001.DAT  ***   [17.30%]
***   E0710091001.DAT  ***   [17.97%]
***   E0710091001.DAT  ***   [18.63%]

I just want to know if I can tell from inside the script if it's being called from cron, and if so, I won't display this output.

Answer 1

you could create a flag. Possibly undocumented that your cron job would pass to the utility to structure the output.

Answer 2

You want to check if you're on a terminal or not. See this stack overflow question: http://stackoverflow.com/questions/911168/detect-if-shell-script-is-running-through-a-pipe

Answer 3

An easy way would be to have the script take an argument that means to suppress that output, and supply that argument when you call it from cron.

Answer 4

I'd check sys.stderr.isatty() -- this way you avoid useless "decoration" output to stderr whenever it wouldn't be immediately perceptible by the user anyway.

Answer 5

See code below. Replace my print statements with what you want to show.

import sys
if sys.stdout.isatty():
    print "Running from command line"
else:
    print "Running from cron"