waitfor

waitfor is a shell app for delaying on conditions. It will simply block until any one of the specified conditions is met. (To require multiple conditions, chain waitfor calls together with &&.)

Condition types

Condition type	Flag	Short	Example	Notes
Time delay	`--elapsed spec`	`-t`	`waitfor --elapsed 10m30s`	Supports only full integer values for `d`, `h`, `m`, and `s`
File existence	`--exists filename`	`-e`	`waitfor --exists foo.txt`	Waits until the file `foo.txt` exists
HTTP GET	`--get [code,]url`	`-g`	`--get http://google.com`	Waits until a GET to Google returns HTTP status code 200
			`--get 404,http://example.com`	Waits until a GET to example.com returns 404
TCP connection	`--tcp host:port`	`-p`	`--tcp 192.168.0.123:22`	Waits until a TCP connection can be made to the specified host. The numeric port must be specified.
File modification date	`--update`	`-u`	`waitfor --update log.txt`	Waits until the modification date on `log.txt` changes. If the modification date can't be retrieved, this condition is ignored
File size	`--size`	`-s`	`waitfor --size log.txt`	Waits until size of `log.txt` changes. The file must exist initially to be included, but if it ceases to exist, the condition will be triggered.

Negation

You can also negate conditions by prefixing the flag with not or by uppercasing the short flag:

Condition type	Flag	Short	Example	Notes
Duration not yet met	`--not-elapsed`	`-T`	`waitfor --not-elapsed 10m`	See comments below
File non-existence	`--not-exists filename`	`-E`	`waitfor --not-exists bar.txt`	Waits until the file `bar.txt` no longer exists
HTTP GET	`--not-get [code,]url`	`-G`	`--not-get http://google.com`	Waits until a GET to Google doesn't return HTTP status code 200
			`--get 404,http://example.com`	Waits until a GET to example.com returns anything but 404
TCP connection	`--not-tcp host:port`	`-P`	`--not-tcp 192.168.0.123:22`	Waits until a TCP connection can not be made to the specified host (either because the host itself is down or the port isn't available).
Modification date stops changing	`--not-update`	`-U`	`waitfor --not-update download.iso`	Waits until the modification date on `download.iso` stops changing. If the modification date can't be retrieved, this condition is ignored. Two identical sequential values trigger this condition.
File size stops changing	`--not-size`	`-S`	`waitfor --not-size download.iso`	Waits until size of `download.iso` stops changing. The file must exist initially to be included, but if it ceases to exist, the condition will be triggered. Two identical sequential values also trigger this condition.

Not-Elapsed

The --not-elapsed flag, by itself, will immediately resolve, but it is intended to be combined with other flags. For example, to delay until a file is deleted but only if it's in the first minute:

waitfor -T 1m -E foo.txt

If foo.txt isn't deleted in the first minute, then the command will block indefinitely. The underlying library, waitforit, allows AND/OR combinations for richer expression.

Additional flags

Flag	Description
`--interval n`	The delay in seconds between checks against the specified condition(s). Default is 2
`--verbose`	Writes some details about status checks to stdout. Without this option, nothing is written.

Multiple conditions

You can combine any number of the above conditions (except --elapsed, which may be used only once), and as soon as any one of them is met, the program will exit. For example, this command will complete when foobar.txt is found or after ten minutes has passed:

waitfor --elapsed 10m --exists foobar.txt

Multiple existence checks are also easy. To wait for either foo.txt or bar.jpg to exist:

waitfor --exists foo.txt --exists bar.jpg

For --exists, you can combine these into a single flag:

waitfor --exists foo.txt,bar.jpg

Nonexistence checks are similar but the inversion. When tmpfile no longer exists (has been deleted or renamed), this command will complete:

waitfor --not-exists tmpfile

The --get flag executes an HTTP GET action against the specified URL, which is assumed to be valid. You may optionally specify any HTTP status code prefixing the URL to wait for that code to be returned, otherwise 200 is assumed. Multiple separate --get flags may be provided, but multiple URLs may not be combined in a single flag. For example:

# Check for either URL to be available as 200 OK:
waitfor --get http://my-site.com/ --get 200,http://your-site.com

# Check for the URL to return 200 or 300
waitfor --get http://my-site.com/ --get 300,http://my-site.com

# Invalid! URLs must be split into two --get flags:
# waitfor --get http://google.com/,http://microsoft.com
# Better:
waitfor --get http://google.com/ --get http://microsoft.com

Because HTTP GET calls incur nontrivial latency, the current implementation counts how long each condition takes to run, and that duration is subtracted from the --interval. That remaining time is spent sleeping. If multiple GETs are called such that the delay exceeds the interval, a new loop will immediately be started. Invocations are not currently parallelized.

aeshirey / waitfor