5 ms·

Show HN: New unix utility "when"

20 points by apgwoz 13y ago

apgwoz 13y ago
I've so far only tested this on OS X, and have mostly used it with the `-t` mode to have it notify me (via "say") when ssh succeeds on a CloudFormation spawned AWS instance.
apetresc 13y ago
I went to go add a Homebrew formula for the name 'when', but it seems to be taken by this command-line calendar app: http://www.lightandmatter.com/when/when.html http://www.lightandmatter.com/when/when.html
- apgwoz 13y ago
  I struggled with a name. This morning in the shower, I liked "trip" but, I'm not sure I'll change it--certainly not because of homebrew.
chingjun 13y ago
What is the difference between this and 'while true; do cmd1 && cmd2; sleep 1; done'
- mooism2 13y ago
  It looks to me more like until cmd1 ; do sleep 1 ; done ; cmd2
  - apgwoz 13y ago
    Exactly. But, see the -t flag, which is the real reason I wrote it. -t is a non-trivial script (if it's even possible in shell). It defaults to the until behavior because it's most common.
    - sciurus 13y ago
      Could you give some more examples of how you use `-t` ?
- d_theorist 13y ago
  Yeah. I was thinking this.
mphillips34 13y ago
watch -n 1 foo && echo "why does this exist?"
- apgwoz 13y ago
  Yes. See the -t flag. That's the reason I wrote it.
lipanski 13y ago
What's the difference between this and the bash '&&' operator? Except for the timebomb flag, I don't really see any difference. Please correct me if I got this wrong. The '&&' operator, as in which ruby && echo 'found it!', triggers the second command, if the exit code of the first one is 0. Also good to note, the '||' operator triggers the second command only if the exit code of the first one is different than 0. As in which ruby123456 || echo 'could not find it!'. EDIT: typo.
- bichiliad 13y ago
  It looks like if the first parameter fails, then it is re-run until it succeeds.
laumars 13y ago
This could be quite handy as need to do this sort of thing surprisingly often and usually resort to a shell script one-liner like this: while true; do echo "hello world"; sleep 3; done While that above code is pretty trivial to type, having a utility to this would be a great time saver for the lazy sysadmin :) edit: someone else just posted about watch[1], never knew that existed before today. You learn something new every day :D [1] https://news.ycombinator.com/item?id=6888640 https://news.ycombinator.com/item?id=6888640

20 points by apgwoz 13y ago

I've so far only tested this on OS X, and have mostly used it with the `-t` mode to have it notify me (via "say") when ssh succeeds on a CloudFormation spawned AWS instance.

apetresc 13y ago

I went to go add a Homebrew formula for the name 'when', but it seems to be taken by this command-line calendar app: http://www.lightandmatter.com/when/when.html http://www.lightandmatter.com/when/when.html

apgwoz 13y ago
I struggled with a name. This morning in the shower, I liked "trip" but, I'm not sure I'll change it--certainly not because of homebrew.

chingjun 13y ago

What is the difference between this and 'while true; do cmd1 && cmd2; sleep 1; done'

mooism2 13y ago
It looks to me more like until cmd1 ; do sleep 1 ; done ; cmd2
- apgwoz 13y ago
  Exactly. But, see the -t flag, which is the real reason I wrote it. -t is a non-trivial script (if it's even possible in shell). It defaults to the until behavior because it's most common.
  - sciurus 13y ago
    Could you give some more examples of how you use `-t` ?
d_theorist 13y ago
Yeah. I was thinking this.

mphillips34 13y ago

watch -n 1 foo && echo "why does this exist?"

apgwoz 13y ago
Yes. See the -t flag. That's the reason I wrote it.

lipanski 13y ago

What's the difference between this and the bash '&&' operator? Except for the timebomb flag, I don't really see any difference. Please correct me if I got this wrong. The '&&' operator, as in which ruby && echo 'found it!', triggers the second command, if the exit code of the first one is 0. Also good to note, the '||' operator triggers the second command only if the exit code of the first one is different than 0. As in which ruby123456 || echo 'could not find it!'. EDIT: typo.

bichiliad 13y ago
It looks like if the first parameter fails, then it is re-run until it succeeds.

laumars 13y ago

This could be quite handy as need to do this sort of thing surprisingly often and usually resort to a shell script one-liner like this: while true; do echo "hello world"; sleep 3; done While that above code is pretty trivial to type, having a utility to this would be a great time saver for the lazy sysadmin :) edit: someone else just posted about watch[1], never knew that existed before today. You learn something new every day :D [1] https://news.ycombinator.com/item?id=6888640 https://news.ycombinator.com/item?id=6888640