Watiba, pronounced wah-TEE-bah, is a lightweight Python pre-compiler for embedding Linux shell commands within Python applications. It is similar to other languages' syntactical enhancements where XML or HTML is integrated into a language such as JavaScript. That is the concept applied here but integrating BASH shell commands with Python.
As you browse this document, you'll find Watiba is rich with features for shell command integration with Python.
Features:
Watiba files, suffixed with ".wt", are Python programs containing embedded shell commands. Shell commands are expressed within backtick characters emulating BASH's original capture syntax. They can be placed in any Python statement or expression. Watiba keeps track of the current working directory after the execution of any shell command so that all subsequent shell commands keep context. For example:
Basic example of embedded commands:
#!/usr/bin/python3
# Typical Python program
if __name__ == "__main__":
# Change directory context
`cd /tmp`
# Directory context maintained
for file in `ls -lrt`.stdout: # In-line access to command results
print(f"File in /tmp: {file}")
This loop will display the file list from /tmp. The ls -lrt is run in the
context of previous cd /tmp.
Commands within backticks can be a variable, but cannot contain snippets of Python code or Python variables. The statement within the backticks must be either a pure shell command or a Python variable containing a pure shell command. To execute commands in a Python variable, prefix the variable name between backticks with a dollar sign.
A command variable is denoted by prepending a dollar sign on the variable name within backticks:
# Set the Python variable to the command
cmdA = 'echo "This is a line of output" > /tmp/blah.txt'
cmdB = 'cat /tmp/blah.txt'
# Execute first command
`$cmdA` # Execute the command within Python variable cmdA
# Execute second command
for line in `$cmdB`.stdout:
print(line)
This example demonstrates keeping dir context and executing a command by variable:
#!/usr/bin/python3
if __name__ == "__main__":
# Change CWD to /tmp
`cd /tmp`
# Set a command string
my_cmd = "tar -zxvf tmp.tar.gz"
# Execute that command and save the command results in variable "w"
w = `$my_cmd`
if w.exit_code == 0:
for l in w.stderr:
print(l)
These constructs are not supported:
file_name = "blah.txt"
# Python variable within backticks
`touch file_name` # NOT SUPPORTED!
# Attempting to access Python variable with dollar sign
`touch $file_name` # NOT SUPPORTED!
# Python within backticks is NOT SUPPORTED!
`if x not in l: ls -lrt x`
An important Watiba usage point is directory context is kept for dispersed shell commands.
Any command that changes the shell's CWD is discovered and kept by Watiba. Watiba achieves
this by tagging a && echo pwd to the user's command, locating the result in the command's STDOUT,
and finally setting the Python environment to that CWD with os.chdir(dir). This is automatic and
opaque to the user. The user will not see the results of the generated suffix. If the echo
suffix presents a problem for the user, it can be eliminated by prefixing the leading backtick with a
dash. The dash turns off the context tracking by not suffixing the command and so causes Watiba to
lose its context. However, the context is maintained within the set of commands in the backticks just not
when it returns. For example, out = -`cd /tmp && ls -lrt` honors the cd within the scope
of that execution line, but not for any backticked commands that follow later in your code.
Warning! The dash will cause Watiba to lose its directory context should the command cause a CWD change either explicitly or implicitly.
Example:
`cd /tmp` # Context will be kept
# This will print from /home/user, but context is NOT kept
for line in -`cd /home/user && ls -lrt`.stdout:
print(line)
# This will print from /tmp, not /home/user
for line in `ls -lrt`.stdout:
print(line)
The results of the command issued in backticks are available in the properties of the object returned by Watiba. Following are those properties:
| Property | Data Type | Description |
|---|---|---|
| stdout | List | STDOUT lines from the command normalized for display |
| stderr | List | STDERR lines from the command normalized for display |
| exit_code | Integer | Exit code value from command |
| cwd | String | Current working directory after command was executed |
Technically, the returned object for any shell command is defined in the WTOutput class.
Shell commands can be executed asynchronously with a defined resolver callback block. Each spawn expression creates
and runs a new OS thread. The resolver is a callback block that follows the Watiba spawn expression. The spawn
feature is executed when a spawn `cmd` args: resolver block code block is encountered. The
resolver is passed the results in the promise object. (The promise structure contains the properties
defined in section "Results from Spawned Commands" The spawn expression also returns a promise object
to the caller of spawn. The promise object is passed to the resolver block in argument promise. The
outer code can check its state with a call to resolved() on the returned promise object. Output from the command
is found in promise.output. The examples throughout this README and in the examples.wt file make this clear.
A promise is either returned in assignment from outermost spawn, or passed to child spawns in argument "promise".
| Property | Data Type | Description |
|---|---|---|
| host | String | Host name on which spawned command ran |
| children | List | Children promises for this promise node |
| parent | Reference | Parent promise node of child promise. None if root promise. |
| command | String | Shell command issued for this promise |
| resolved() | Method | Call to find out if this promise is resolved |
| resolve_parent() | Method | Call inside resolver block to resolve parent promise |
| tree_dump() | Method | Call to show the promise tree. Takes subtree argument otherwise it defaults to the root promise |
| join() | Method | Call to wait on on promise and all its children |
| wait() | Method | Call to wait on just this promise |
| watch() | Method | Call to create watcher on this promise |
| start_time | Time | Time that spawned command started |
| end_time | Time | Time that promise resolved |
Example of simple spawn:
prom = spawn `tar -zcvf big_file.tar.gz some_dir/*`:
# Resolver block to which "promise" and "args" is passed...
print(f"{promise.command} completed.")
return True # Resolve promise
# Do other things while tar is running
# Finally wait for tar promise to resolve
prom.join()
All spawned threads are managed by Watiba's Spawn Controller. The controller watches for too many threads and
incrementally slows down each thread start when that threshold is exceeded until either all the promises in the tree
resolve, or an expiration count is reached, at which time an exception is thrown on the last spawned command.
This exception is raised by the default error method. This method as well as other spawn controlling parameters
can be overridden. The controller's purpose is to not allow run away threads and provide signaling of possible
hung threads.
spawn-ctl example:
# Only allow 20 spawns max,
# and increase slowdown by 1/2 second each 3rd cycle
...python code...
spawn-ctl {"max":20, "sleep-increment":.500}
Spawn control parameters:
| Key Name | Data Type | Description | Default |
|---|---|---|---|
| max | Integer | The maximum number of spawned commands allowed before the controller enters slowdown mode | 10 |
| sleep-floor | Integer | Seconds of starting sleep value when the controller enters slowdown mode | .125 (start at 1/8th second pause) |
| sleep-increment | Integer | Seconds the amount of seconds sleep will increase every 3rd cycle when in slowdown mode | .125 (Increase pause 1/8th second every 3rd cycle) |
| sleep-ceiling | Integer | Seconds the highest length sleep value allowed when in slowdown mode (As slow as it will get) | 3 (won't get slower than 3 second pauses) |
| expire | Integer | Total number of slowdown cycles allowed before the error method is called | No expiration |
| error | Method |
Callback method invoked when slowdown mode expires. Use this to catch hung commands.
This method is passed 2 arguments:
| Generic error handler. Just throws WTSpawnException that hold properties promise and message |
spawn-ctl only overrides the values it sets and does not affect values not specified. spawn-ctl statements can set whichever values it wants, can be dispersed throughout your code (i.e. multiple spawn-ctl statements) and only affects subsequent spawn expressions.
Notes:
args
of the spawn expression will only be shallow copied so if there are references to other objects, it's not likely to
survive the copy.promise.set_resolved(). This is handy in cases where
a resolver has spawned another command and doesn't want the outer promise resolved until the inner resolvers are done.
To resolve an outer, i.e. parent, resolver issue promise.resolve_parent(). Then the parent resolver can return
False at the end of its block so it leaves the resolved determination to the inner resolver block.Spawn Syntax:
my_promise = spawn `cmd` [args]:
resolver block (promise, args)
args passed in args
return resolved or unresolved (True or False)
Spawn with resolver arguments omitted:
my_promise = spawn `cmd`:
resolver block (promise, args)
return resolved or unresolved (True or False)
Simple spawn example:
p = spawn `tar -zcvf /tmp/file.tar.gz /home/user/dir`:
# Resolver block to which "promise" and "args" are passed
# Resolver block is called when spawned command has completed
for line in promise.output.stderr:
print(line)
# This marks the promise resolved
return True
# Wait for spawned command to resolve (not merely complete)
try:
p.join({"expire": 3})
print("tar resolved")
except Exception as ex:
print(ex.args)
Example of file that overrides spawn controller parameters:
#!/usr/bin/python3
def spawn_expired(promise, count):
print("I do nothing just to demonstrate the error callback.")
print(f"This command failed {promise.command} at this threshold {count}")
raise Exception("Too many threads.")
if __name__ == "__main__":
# Example showing default values
parms = {"max": 10, # Max number of threads allowed before slowdown mode
"sleep-floor": .125, # Starting sleep value
"sleep-ceiling": 3, # Maximum sleep value
"sleep-increment": .125, # Incremental sleep value
"expire": -1, # Default: no expiration
"error": spawn_expired # Method called upon slowdown expiration
}
# Set spawn controller parameter values
spawn-ctl parms
Once commands are spawned, the caller can wait for all promises, including inner or child promises, to complete, or the caller can wait for just a specific promise to complete. To wait for all child promises including the promise on which you're calling this method, call join(). It will wait for that promise and all its children. To wait for just one specific promise, call wait() on the promise of interest. To wait for all promises in the promise tree, call join() on the root promise.
join and wait can be controlled through parameters. Each are iterators paused with a sleep method and will throw an expiration exception should you set a limit for iterations. If an expiration value is not set, no exception will be thrown and the cycle will run only until the promise(s) are resolved. join and wait are not affected by spawn-ctl.
watch is called to establish a separate asynchronous thread that will call back a function of your choosing should the command the promise is attached to time out. This is different than join and wait in that watch is not synchronous and does not pause. This is used to keep an eye on a spawned command and take action should it hang. Your watcher function is passed the promise on which the watcher was attached, and the arguments, if any, from the spawn expression. If your command does not time out (i.e. hangs and expires), the watcher thread will quietly go away when the promise is resolved. watch expiration is expressed in seconds, unlike join and wait which are expressed as total iterations paused at the sleep value. watch's polling cycle pause is .250 seconds, so the expiration value is multiplied by 4. The default expiration is 15 seconds.
Examples:
# Spawn a thread running this command
p = spawn `ls -lrt`:
## resolver block ##
return True
# Wait for promises, pause for 1/4 second each iteration, and throw an exception after 4 iterations
(1 second)
try:
p.join({"sleep": .250, "expire": 4})
except Exception as ex:
print(ex.args)
# Wait for this promise, pause for 1 second each iteration, and throw an exception after 5 iterations
(5 seconds)
try:
p.wait({"sleep": 1, "expire": 5})
except Exception as ex:
print(ex.args)
# My watcher function (called if spawned command never resolves by its experation period)
def watcher(promise, args):
print(f"This promise is likely hung: {promise.command}")
print(f"and I still have the spawn expression's args: {args}")
p = spawn `echo "hello" && sleep 5` args:
print(f"Args passed to me: {args}")
return True
# Attach a watcher to this thread. It will be called upon experation.
p.watch(watcher)
print("watch() does not pause like join or wait")
# Attach a watcher that will expire in 5 seconds
p.watch(watcher, {"expire": 5})
join syntax
promise.join({optional args})
Where args is a Python dictionary with the following options:
"sleep" - seconds of sleep for each iteration (fractions such as .5 are honored)
default: .5 seconds
"expire" - number of sleep iterations until an excpetions is raised
default: no expiration
Note: "args" is optional and can be omitted
Example of joining parent and children promises:
p = spawn `ls *.txt`:
for f in promise.output.stdout:
cmd = f"tar -zcvf {f}.tar.gz {f}"
spawn `$cmd` {"file":f}:
print(f"{f} completed")
promise.resolve_parent()
return True
return False
# Wait for all commands to complete
try:
p.join({"sleep":1, "expire":20})
except Exception as ex:
print(ex.args)
wait syntax
promise.wait({optional args})
Where args is a Python dictionary with the following options:
"sleep" - seconds of sleep for each iteration (fractions such as .5 are honored)
default: .5 seconds
"expire" - number of sleep iterations until an excpetions is raised
default: no expiration
Note: "args" is optional and can be omitted
Example of waiting on just the parent promise:
p = spawn `ls *.txt`:
for f in promise.output.stdout:
cmd = f"tar -zcvf {f}.tar.gz {}"
spawn `$cmd` {"file":f}:
print(f"{f} completed")
promise.resolve_parent() # Wait completes here
return True
return False
# Wait for just the parent promise to complete
try:
p.wait({"sleep":1, "expire":20})
except Exception as ex:
print(ex.args)
watch syntax
promise.watch(callback, {optional args})
Where args is a Python dictionary with the following options:
"sleep" - seconds of sleep for each iteration (fractions such as .5 are honored)
default: .5 seconds
"expire" - number of sleep iterations until an excpetions is raised
default: no expiration
Note: "args" is optional and can be omitted
Example of creating a watcher:
# Define watcher method. Called if command times out (i.e. expires)
def time_out(promise, args):
print(f"Command {promise.command} timed out.")
# Spawn a thread running some command that hangs
p = spawn `long-running.sh`:
print("Finally completed. Watcher method won't be called.")
return True
p.watch(time_out) # Does not wait. Calls method "time_out" if this promise expires (i.e. command hangs)
# Do other things...
Each spawn issued inserts its promise object into the promise tree. The outermost spawn will generate the root promise and each inner spawn will be among its children. There's no limit to how far it can nest. wait only applies to the promise on which it is called and is how it is different than join. wait does not consider any other promise state but the one it's called for, whereas join considers the one it's called for and anything below it in the tree.
The promise tree can be printed with the dump_tree() method on the promise. This method is intended for
diagnostic purposes where it must be determined why spawned commands hung. dump_tree(subtree) accepts
a subtree promise as an argument. If no arguments are passed, dump_tree() dumps from the root promise on down.
# Simple example with no child promises
p = spawn `date`:
return True
p.tree_dump() # Dump tree from root
# or
p.tree_dump(subtree_promise) # Dump tree from node in argument
Example dumping tree from subtree node:
# Complex example with child and grandchild promises
# Demonstrates how to dump the promise tree from various points within it
p = spawn `date`:
# Spawn child command (child promise)
spawn `pwd`:
# Spawn a grandchild to the parent promise
spawn `python --version`:
promise.tree_dump(promise) # Dump the subtree from this point down
return False
# Spawn another child
spawn `echo "blah"`:
# Resolve parent promise
promise.resolve_parent()
# Resolve child promise
return True
# Do NOT resolve parent promise, let child do that
return False
p.join()
p.tree_dump(p.children[0]) # Dump subtree from first child on down
p.tree_dump(p.children[1]) # Dump subtree from the second child
p.tree_dump(p.children[0].children[0]) # Dump subtree from the grandchild
# Dump all children
for c in p.children:
p.tree_dump(c)
Parent and child joins shown in these two examples:
root_promise = spawn `ls -lr`:
for file in promise.stdout:
t = f"touch {file}"
spawn `$t` {"file" file}: # This promise is a child of root
print(f"{file} updated".)
spawn `echo "done" > /tmp/done"`: # Another child promise (root's grandchild)
print("Complete")
promise.resolve_parent()
return True
promise.resolve_parent()
return False
return False
root_promise.join() # Wait on the root promise and all its children. Thus, waiting for everything.
root_promise = spawn `ls -lr`:
for file in promise.output.stdout:
t = f"touch {file}"
spawn `$t` {"file" file}: # This promise is a child of root
print(f"{promise.args['file'])} updated")
promise.join() # Wait for this promise and its children but not its parent (root)
spawn `echo "done" > /tmp/done"`:
print("Complete")
Resolving a parent promise:
p = spawn `ls -lrt`:
for f in promise.output.stdout:
cmd = f"touch {f}"
# Spawn command from this resolver and pass our promise
spawn `$cmd`:
print("Resolving all promises")
promise.resolve_parent() # Resolve parent promise here
return True # Resolve child promise
return False # Do NOT resolve parent promise here
p.join() # Wait for ALL promises to be resolved
Spawned commands return their results in the promise.output property of the promise object passed to the resolver block, and in the spawn expression if there is an assignment in that spawn expression.
The result properties can then be accessed as followed:
| Property | Data Type | Description |
|---|---|---|
| promise.output.stdout | List | STDOUT lines from the command normalized for display |
| promise.output.stderr | List | STDERR lines from the command normalized for display |
| promise.output.exit_code | Integer | Exit code value from command |
| promise.output.cwd | String | Current working directory after command was executed |
Notes:
Simple example with the shell command as a Python variable:
#!/usr/bin/python3
# run "date" command asynchronously
d = 'date "+%Y/%m/%d"'
spawn `$d`:
print(promise.output.stdout[0])
return True
Example with shell commands executed within resolver block:
#!/usr/bin/python3
print("Running Watiba spawn with wait")
`rm /tmp/done`
# run "ls -lrt" command asynchronously
p = spawn `ls -lrt`:
print(f"Exit code: {promise.output.exit_code}")
print(f"CWD: {promise.output.cwd}")
print(f"STDERR: {promise.output.stderr}")
# Loop through STDOUT from command
for l in promise.output.stdout:
print(l)
`echo "Done" > /tmp/done`
# Resolve promise
return True
# Pause until spawn command is complete
p.wait()
print("complete")
Each promise produced from a spawn expression results in one OS thread. To access the number of threads your code has spawned collectively, you can do the following:
num_of_spawns = promise.spawn_count() # Returns number of nodes in the promise tree
num_of_resolved_promises = promise.resolved_count() # Returns the number of promises resolved in tree
Shell commands can be executed remotely. This is achieved though the SSH command, issued by Watiba, and has the following requirements:
OpenSSH is installed on the local and remote hosts
The local SSH key is in the remote's authorized_keys file. The details of this process is beyond the scope of this README. For those instructions, consult www.ssh.com
Make sure that SSH'ing to the target host does not cause any prompts.
Test that your SSH environment is setup first by manually entering:
ssh {user}@{host} "ls -lrt"
# For example
ssh rwalk@walkubu "ls -lrt"
# If SSH prompts you, then Watiba remote execution cannot function.
To execute a command remotely, a @host parameter is suffixed to the backticked command. The host name can be a literal or a variable. To employ a variable, prepend a $ to the name following @ such as @$var.
To change the default SSH port 22 to a custom value, add to your Watiba code: watiba-ctl {"ssh-port": custom port}
Example:
watiba-ctl {"ssh-port": 2233}
Examples:
p = spawn `ls -lrt`@remoteserver {parms}:
for line in promise.output.stdout:
print(line)
return True
remotename = "serverB"
p = spawn `ls -lrt`@$remotename {parms}:
for line in p.output.stdout:
print(line)
return True
out = `ls -lrt`@remoteserver
for line in out.stdout:
print(line)
remotename = "serverB"
out = `ls -lrt`@$remotename
for line in out.stdout:
print(line)
Hooks are pre- or -post functions that are attached to a command pattern, which is a regular expression (regex). Anytime Watiba encounters a command that matches the pattern for the hook, the hook function is called.
All commands, spawned, remote, or local, can have Python functions executed before exection, by default, or post hooks that are run after the command. (Note: Post hooks are not run for spwaned commands because the resolver function is a post hook itself.) These functions can be passed arguments, too.
# Run before commands that match that pattern
hook-cmd "pattern" hook-function parms
# Run before commands that match that pattern, but is non-recursive
hook-cmd-nr "pattern" hook-function parms
# Run after commands that match that pattern
post-hook-cmd "pattern" hook-function parms
# Run after commands that match that pattern, but is non-recursive
post-hook-cmd-nr "pattern" hook-function parms
Hooks, which are nothing more than Python functions called before or after a command is run, can issue their own commands and, thus, cause the hook to be recursively called. However, if the command in the hook block of code matches a command pattern that causes that same hook function to be run again, an infinte loop can occur. To prevent that, use the -nr suffix on the Watiba hook expression. (-nr stands for non-recursive.) This will ensure that the hook cannot be re-invoked for any commands that are within it.
hook-cmd "command pattern" function parms
The first parameter always passed to the hook function is the Python match object from the command match. This is provided so the hook has access to the tokens on the command should it need them.
Example:
def my_hook(match, parms):
print(match.groups())
print(f'Tar file name is {match.group(1)}')
print(parms["parmA"])
print(parms["parmB"])
return True # Successful execution
def your_hook(match, parms):
# This hook doesn't need the match object, so ignores it
print(parms["something"])
if parms["something-else"] != "blah":
return False # Failed execution
return True # Successful excution
# Add first hook to my tar command
hook-cmd "tar -zcvf (\S.*)" my_hook: {"parmA":"A", "parmB":"B"}
# Add another hook to my tar command
hook-cmd "tar -zcvf (\S.*)" your_hook: {"parmD":1, "parmE":"something"}
# Spawn command, but hooks will be invoked first...
spawn `tar -zcvf files.tar.gz /tmp/files/* `:
# Resolver code block
return True # Resolve promise
Your parameters are whatever is valid for Python. These are simply passed to their attached functions, essentially each one's key is the function name, as specified.
Where are the hooks run for spawned commands? All hooks run under the thread of the issuer on the local host, not the target thread.
Where are the hooks run for remote commands? As with spawned commands, all hooks are issued on the local host, not the remote. Note that you can have remote backticked commands in your hook and that will run those remotely. If your remote command matches a hook(s) pattern, then those hooks will be run. This means if your command pattern for the first remote call runs a hook that contains another remote command that matches that same command pattern, then the hook is run again. Since this can lead to infinte hook loops, Watiba offers a non-recursive definition for the command pattern. Note that this non-recursive setting only applies to the command pattern and not the hook function itself. So if hookA is run for two different command patterns, say, "ls -lrt" and "ls -laF" you can make one non-recusrive and still run the same hook for both commands. For the recursive command pattern, the hook has no limit to its recursion. For non-recursive, it will only be called once during the recursion process.
To set a command pattern as non-recursive, use hook-cmd-nr.
Example using a variation on a previous example:
def my_hook(match, parms)
`tar -zcvf /tmp/files` # my_hook will NOT because for this command even though it matches
print("Will be called only once!")
return True
# Note the "-nr" on the expression. That's for non-recursive
hook-cmd-nr "tar -zcvf (\S.*)" my_hook: {"parmA":"A", "parmB":"B"}
# my_hook will be called before this command runs
` tar -zcvf tarball.tar.gz /home/user/files.*`
Watiba extends its remote command execution to chaining commands across multiple remote hosts. This is achieved by the chain expression. This expression will execute the backticked command across a list of hosts, passed by the user, sequentially, synchronously until the hosts list is exhausted, or the command fails. chain returns a Python dictionary where the keys are the host names and the values the WTOutput from the command run on that host.
The chain expression raises a WTChainException on the first failed command. The exception raised has the following properties:
WTChainException:
| Property | Data Type | Description |
|---|---|---|
| command | String | Command that failed |
| host | String | Host where command failed |
| message | String | Error message |
| output | WTOutput structure:
| Output from command |
Import this exception to catch it:
from watiba import WTChainException
Examples:
from watiba import WTChainException
try:
out = chain `tar -zcvf backup/file.tar.gz dir/*` {"hosts", ["serverA", "serverB"]}
for host,output in out.items():
print(f'{host} exit code: {output.exit_code}')
for line in output.stderr:
print(line)
except WTChainException(ex):
print(f"Error: {ex.message}")
print(f" host: {ex.host} exit code: {ex.output.exit_code} command: {ex.command})
The chain expression supports piping STDOUT and/or STDERR to other commands executed on remote servers. Complex arrangements can be constructed through the Python dictionary passed to the chain expression. The dictionary contents function as follows:
"hosts": [server, server, ...] This entry instructions chain on which hosts the backticked command will run. This is a required entry.
"stdout": {server:command, server:command, ...} This is an optional entry.
"stderr": {server:command, server:command, ...} This is an optional entry.
Just like a chain expression that does not pipe output, the return object is a dictionary of WTOutput object keyed by the host name from the hosts list and not from the commands recieving the piped output.
If any command fails, a WTChainException is raised. Import this exception to catch it:
from watiba import WTChainException
Note: The piping feature is experimental as of this release, and a better design will eventually supercede it.
Examples:
from watiba import WTChainException
# This is a simple chain with no piping
try:
args = {"hosts": ["serverA", "serverB", "serverC"]}
out = chain `ls -lrt dir/` args
for host, output in out.items():
print(f'{host} exit code: {output.exit_code}')
except WTChainException as ex:
print(f'ERROR: {ex.message}, {ex.host}, {ex.command}, {ex.output.stderr}')
# This is a more complex chain that runs the "ls -lrt" command on each server listed in "hosts"
# and pipes the STDOUT output from serverC to serverV and serverD, to those commands, and serverB's STDERR
# to serverX and its command
try:
args = {"hosts": ["serverA", "serverB", "serverC"],
"stdout": {"serverC":{"serverV": "grep something", "serverD":"grep somethingelse"}},
"stderr": {"serverB":{"serverX": "cat >> /tmp/serverC.err"}}
}
out = chain `ls -lrt dir/` args
for host, output in out.items():
print(f'{host} exit code: {output.exit_code}')
except WTChainException as ex:
print(f'ERROR: {ex.message}, {ex.host}, {ex.command}, {ex.output.stderr}')
####How does this work? Watiba will run the backticked command in the expression on each host listed in hosts, in sequence and synchronously. If there is a "stdout" found in the arguments, then it will name the source host as the key, i.e. the host from which STDOUT will be read, and fed to each host and command listed under that host. This is true for STDERR as well.
The method in which Watiba feeds the piped output is through a an echo command shell piped to the command to be run
on that host. So, "stdout": {"serverC":{"serverV": "grep something"}} causes Watiba to read each line of STDOUT from
serverC and issue echo "$line" | grep something on serverV. It is piping from serverC to serverV.
If you installed this as a Python package, e.g. pip, then the pre-compiler, watiba-c, will be placed in your system's PATH by PIP.
If you cloned this from github, you'll still need to install the package with pip, first, for the watbia module. Follow these steps to install Watiba locally.
# Watiba package required
python3 -m pip install watiba
Test that the pre-compiler functions in your environment:
watiba-c version
For example:
rwalk@walkubu:~$ watiba-c version
Watiba 0.3.26
To pre-compile a .wt file:
watiba-c my_file.wt > my_file.py
chmod +x my_file.py
./my_file.py
Where my_file.wt is your Watiba code.
my_file.wt
#!/usr/bin/python3
# Stand alone commands. One with directory context, one without
# This CWD will be active until a subsequent command changes it
`cd /tmp`
# Simple statement utilizing command and results in one statement
print(`cd /tmp`.cwd)
# This will not change the Watiba CWD context, because of the dash prefix, but within
# the command itself the cd is honored. file.txt is created in /home/user/blah but
# this does not impact the CWD of any subsequent commands. They
# are still operating from the previous cd command to /tmp
-`cd /home/user/blah && touch file.txt`
# This will print "/tmp" _not_ /home because of the leading dash on the command
print(f"CWD is not /home: {-`cd /home`.cwd)}"
# This will find text files in /tmp/, not /home/user/blah (CWD context!)
w=`find . -name '*.txt'`
for l in w.stdout:
print(f"File: {l}")
# Embedding commands in print expressions that will print the stderr output, which tar writes to
print(`echo "Some textual comment" > /tmp/blah.txt && tar -zcvf /tmp/blah.tar.gz /tmp`).stdout)
# This will print the first line of stdout from the echo
print(`echo "hello!"`.stdout[0])
# Example of more than one command in a statement line
if len(`ls -lrt`.stdout) > 0 or len(-`cd /tmp`.stdout) > 0:
print("You have stdout or stderr messages")
# Example of a command as a Python varible and
# receiving a Watiba object
cmd = "tar -zcvf /tmp/watiba_test.tar.gz /mnt/data/git/watiba/src"
cmd_results = `$cmd`
if cmd_results.exit_code == 0:
for l in cmd_results.stderr:
print(l)
# Simple reading of command output
# Iterate on the stdout property
for l in `cat blah.txt`.stdout:
print(l)
# Example of a failed command to see its exit code
xc = `lsvv -lrt`.exit_code
print(f"Return code: {xc}")
# Example of running a command asynchronously and resolving promise
spawn `cd /tmp && tar -zxvf tarball.tar.gz`:
for l in promise.output.stderr:
print(l)
return True # Mark promise resolved
# List dirs from CWD, iterate through them, spawn a tar command
# then within the resolver, spawn a move command
# Demonstrates spawns within resolvers
for dir in `ls -d *`.stdout:
tar = "tar -zcvf {}.tar.gz {}"
prom = spawn `$tar` {"dir": dir}:
print(f"{}args['dir'] tar complete")
mv = f"mv -r {args['dir']}/* /tmp/."
spawn `$mv`:
print("Move done")
# Resolve outer promise
promise.resolve_parent()
return True
# Do not resolve this promise yet. Let the inner resolver do it
return False
prom.join()
FAQs
Python syntactical sugar for embedded shell commands
We found that watiba demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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