5

I've got a script like the following:

flag=false
# Do a bunch of stuff that might set flag to true.
if [[ "$flag" == "true" ]]; then
   command \
       | pipe_command_a \
       | pipe_command_b \
       | pipe_command_c \
       | pipe_command_d \
       > "${output_path}"
else
   command \
       | pipe_command_a \
       | pipe_command_c \
       | pipe_command_d \
       > "${output_path}"
fi

The only difference between flag being true or false makes is that pipe_command_b may not be run. Is there a way to collapse this so that I don't have to repeat all of the common stuff?

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1 Answer 1

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6

Use cat instead of the command if you want to skip it:

command=cat
if [[ $flag == true ]] ; then
    command=pipe_command_b
fi
command \
    | pipe_command_a \
    | $command       \
    | pipe_command_c
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  • 1
    Isn't it possible that piping cat into certain commands may break things? Commented Aug 3, 2017 at 17:45
  • @Jesse_b: They seem to pipe the output to pipe_command_c anyway. Commented Aug 3, 2017 at 17:47
  • yea but cat also changes some results. The only one I can think of now is ls which you wouldn't want to use in a pipeline anyway but ls | cat provides a different result than just ls Commented Aug 3, 2017 at 17:50
  • 1
    @Jesse_b: Still the same reply. The only problem with that is when the command is the last one in the pipeline. Commented Aug 3, 2017 at 18:25
  • 3
    @Jesse_b that isn't cat "changing some results". That's ls detecting that its stdout is not a tty and producing different output (i.e. one filename per line rather than multiple filenames on multi-column line(s)). Commented Aug 4, 2017 at 6:47

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