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How can I tell (in ~/.bashrc) if I'm running in interactive mode, or, say, executing a command over ssh. I want to avoid printing of ANSI escape sequences in .bashrc if it's the latter.

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3 Answers 3

up vote 21 down vote accepted

According to man bash:

PS1 is set and $- includes i if bash is interactive, allowing a shell script or a startup file to test this state.

So you can use:

if [[ $- == *i* ]]
then
    do_interactive_stuff
fi

Also:

When an interactive shell that is not a login shell is started, bash reads and executes commands from /etc/bash.bashrc and ~/.bashrc, if these files exist.

So ~/.bashrc is only sourced for interactive shells. Sometimes, people source it from ~/.bash_profile or ~/.profile which is incorrect since it interferes with the expected behavior. If you want to simplify maintenance of code that is common, you should use a separate file to contain the common code and source it independently from both rc files.

It's best if there's no output to stdout from login rc files such as ~/.bash_profile or ~/.profile since it can interfere with the proper operation of rsync for example.

In any case, it's still a good idea to test for interactivity since incorrect configuration may exist.

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Note that $- may contain an i, not necessarily equal it. I use [[ $- =~ i ]] && echo interactive –  Alex Howansky Feb 27 '13 at 14:47
    
@AlexHowansky: the asterisks in the equality test make it a test for containing i –  Dennis Williamson Feb 27 '13 at 18:17
    
Oh wow didn't even notice those, they look like double quotes on my monitor. It may be time to up the font size. <getting old> –  Alex Howansky Feb 28 '13 at 14:29
    
Sometimes, people source it from ~/.bash_profile or ~/.profile which is incorrect since it interferes with the expected behavior Right. What do you think of sourcing ~/.bashrc from ~/.bash_login? As login shell needn't to to be interactive I guess it's incorrect, too. –  Piotr Dobrogost Mar 5 at 20:44
    
@PiotrDobrogost: This is an excellent discussion of shell startup files. –  Dennis Williamson Mar 6 at 2:11

I typically look at the output of the program tty.

If you're on a tty, it will tell you which tty you're on. If you're not in interactive mode, it will typically tell you something like "not a tty".

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3  
tty -s will set a return value of 0 if you are on a terminal or 1 otherwise without giving you output. You can use it as 'if tty -s; then _interactive; fi' –  BillThor May 31 '10 at 1:31
    
Thanks! It's been a long time since I've needed to do this sort of thing and I guess I forgot some of the details... –  chris May 31 '10 at 11:13

Use:

if tty -s; then echo interactive; fi
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