Shell Tricks: Detecting if your script is being piped

If you need to check if a shell script is being piped to another program (i.e. bash yourscript.sh | less) you can use test -t 1 and friends.

I use this in most scripts that I have that output some kind of color or special formatting. That way if I pipe them to a different program it receives input without any colors.

Suppose you have example.sh:

#!/usr/bin/env bash
 
if [[ -t 1 ]]; then
  printf "\e[031%s\e[0m\n" "Danger!"
else
  echo "Danger!"
fi

If you run bash example.sh you’ll see “Danger!” in red text. But, if you run bash example.sh | cat you’ll see “Danger!” in your default text color.

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Note: test is the same as [, while Bash/ZSH also have [[ which accepts the same arguments as test but adds new behavior. You probably always want to use [[ unless you’re targeting POSIX sh.