loop 
"UNIX's missing loop command!"
loop lets you write powerful, intuitive looping one-liners in your favorite shell! Finally, loops in Bash that make sense!
Why?
Loops in bash are surprisingly complicated and fickle! I wanted a simple and intuitive way to write controllable loops that run on timers, have custom counters, loop until output matches certain conditions, and iterate over the standard input. And so loop was born!
Installation
Linux
TODO! See here.
OSX
If you're a Homebrew user:
$ brew tap miserlou/loop https://github.com/Miserlou/Loop.git
$ brew install loop --HEAD
Rust Users
$ cargo install loop-rs
Building
$ cargo build
./debug/loop
Publishing
$ cargo build
./debug/loop
Usage
Counters
loop places the a counter value into the $COUNT enviornment variable.
$ loop 'echo $COUNT'
0
1
2
[ .. ]
The amount this counter increments can be changed with --count-by:
$ loop 'echo $COUNT' --count-by 2
2
4
6
[ .. ]
The counter can be offset with --offset:
$ loop 'echo $COUNT' --count-by 2 --offset 10
10
12
14
[ .. ]
And iterators can be floats!
$ loop 'echo $COUNT' --count-by 1.1
0
1.1
2.2
[ .. ]
There's also an $ACTUALCOUNT:
$ loop 'echo $COUNT $ACTUALCOUNT' --count-by 2
0 0
2 1
4 2
[ .. ]
Timed Loops
Loops can be set to timers which accept humanized times from the microsecond to the year with --every:
$ loop 'date' --every 5s
Thu May 17 10:51:03 EDT 2018
Thu May 17 10:51:08 EDT 2018
Thu May 17 10:51:13 EDT 2018
Looping can be limited to a set duration with --for-duration:
$ loop 'date' --for-duration 8s --every 2s
Fri May 25 16:46:42 EDT 2018
Fri May 25 16:46:44 EDT 2018
Fri May 25 16:46:46 EDT 2018
Fri May 25 16:46:48 EDT 2018
$
Or until a certain date/time with --until-time:
$ loop 'date -u' --until-time '2018-05-25 20:50:00' --every 5s
Fri May 25 20:49:49 UTC 2018
Fri May 25 20:49:54 UTC 2018
Fri May 25 20:49:59 UTC 2018
$
Until Conditions
loop can interate until output contains a string with --until-contains:
$ loop 'echo $RANDOM' --until-contains "666"
11235
35925
666
$
Or until a program succeeds with --until-success:
$ loop "if (( RANDOM % 2 )); then (echo "TRUE"; true); else (echo "FALSE"; false); fi" --until-success
FALSE
FALSE
TRUE
$
Or until it fails with --until-error (which also accepts an optional error code):
$ loop "if (( RANDOM % 2 )); then (echo "TRUE"; true); else (echo "FALSE"; false); fi" --until-error
TRUE
TRUE
FALSE
$
Or until it matches a regular expression with --until-error:
$ loop 'date' --until-match "(\d{4})"
Thu May 17 10:51:03 EDT 2018
$
Iterating Over Lists and Standard Inputs
Loops can iterate over all sorts of lists with --for:
$ loop 'echo $ITEM' --for red,green,blue
red
green
blue
$
And can read from the standard input via pipes:
$ cat my-list-of-files-to-create.txt | loop 'touch $ITEM'
$ ls
hello.jpg
goodbye.jpg
..or via the keyboard with -i:
$ loop 'echo $ITEM | tr a-z A-Z' -i
hello
world^D
HELLO
WORLD
--for can accept all sorts of lists:
$ loop 'echo $ITEM' --for "`ls`"
Cargo.lock
Cargo.toml
README.md
src
target
$
License
(c) Rich Jones, 2018. MIT License.