Home / server / Questions / 776465
In Process
hyperknot
Asked: 2016-05-13 11:36:43 +0800 CST

ps aux | grep result depends on terminal size on FreeBSD

  • 772

From experimenting, it seems that even when using ps aux | grep ... the output depends on the terminal size. This seems seriously weird for me.

Isn't a pipe supposed to make command's output behave in a predictable way?

For example ls does all fancy formatting magic when run on its own, but when run like ls | less it always returns the same output styling.

But unlike ls, the output from ps aux | less cuts the lines to terminal width on FreeBSD (on bash at least). From my brief experimenting, the same command always outputs full length lines in Linux when used with pipes.

Why is this happening and how can I fix it?

Is this just a really weird FreeBSD default? From my understanding this "feature" would make it almost impossible to write reliable bash scripts on FreeBSD as the output of simple piped commands would not be reliable. Isn't this a problem?

Update: Thanks to Bert, I've tried it with ps aux > somefile and the lines inside the file are cut exactly like how it was with grep and less!

Info: FreeBSD 10.2, bash 4.3.42, same when connecting over SSH or when logged in locally via KVM.

linux bash freebsd

1 Answers

  1. It's not the piping doing it. Part of your problem is your pager, less. By default it truncates at the same length as your terminal does. You can fix this by telling it not to do that:

    ps aux | less -S

    ps detects the window width and outputs to fit

    The man page has one way to bypass this:

    -w Use 132 columns to display information, instead of the default which is your window size. If the -w option is specified more than once, ps will use as many columns as necessary without regard for your window size. Note that this option has no effect if the “command” column is not the last column displayed.

    Another solution would be to pipe the output to a file

    ps aux > somefile

    • 1