CODEWITHSUNDEEP
unixemacs
Palace Chan
Palace Chan

Reputation: 9213

Do commands run considerably slower in the emacs shell? How can I prevent this but still use it?

Today I ran a command like this in the emacs shell:

./someBinary | grep foo | cut -c30- | sort | uniq -c

which in bash takes a bit but not that long (about 15 seconds) because the output is over a million lines easily. When I ran this command in the emacs shell, however, I waited over an hour and it's still running, with the processes visibly doing work if i check with top. I wonder if this is because emacs implements the unix tools I am piping to in lisp - and if this is the reason, if there's a way to have it default to the system ones.

Upvotes: 5

Views: 1200

Answers (3)

unhammer
unhammer

Reputation: 4740

You don't say whether you use eshell or shell. In my experience, shell works just fine, but eshell is completely unusable for anything that wants to put >1k lines through a pipe (which is sad, because the other features of eshell look quite nice).

Note eshell is slow even if output is just one line, as long as you use a |, so it seems to be the actual | operator (that's implemented in emacs-lisp in eshell) that's being slow.

Upvotes: 0

user4815162342
user4815162342

Reputation: 155406

Emacs is capturing the final output in the shell buffer, and applying font-lock and other analysis (line number counting, for example) to display it. It also scrolls the display to show the latest output. While Emacs has provisions for culling pathologically long command output, it's not really optimized for truly huge quantities of output counting in millions of lines, so it performs visibly worse than your terminal emulator, slowing down the whole pipeline.

If you're not interested in the output, redirect it to /dev/null or to tail -500, which is how much you'd see of it in a typical terminal scrollback anyway.

Upvotes: 3

jtahlborn
jtahlborn

Reputation: 53694

no, emacs does not implement those tools. that is running the same tools you run from the command line. however, the output is being passed through various pipes and probably has various formatting applied by emacs, which is most likely the culprit for the extreme slowdown. one easy thing to try would be disabling font-lock mode in the shell buffer.

Upvotes: 2

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