Tag: loops

How to iterate over a dictionary and operate with its elements?

I have this dictionary, where the keys represent atom types and the values represent the atomic masses:

mass = {'H': 1.007825, 'C': 12.01, 'O': 15.9994, 'N': 14.0067, 'S': 31.972071,
        'P': 30.973762}

what I want to do is to create a function that given a molecule, for instance ('H2-N-C6-H4-C-O-2H'), iterates over the mass dictionary and calculates the atomic mass on the given molecule. The value of the mass must be multiplied by the number that comes right after the atom type: H2 = H.value * 2

I know that firstly I must isolate the keys of the given molecules, for this I could use string.split('-'). Then, I think I could use and if block to stablish a condition to accomplish if the key of the given molecule is in the dictionary. But later I’m lost about how I should proceed to find the mass for each key of the dictionary.

The expected result should be something like:

mass_counter('H2-N15-P3')

out[0] 39351.14

How could I do this?

EDIT:

This is what I’ve tried so far

# Atomic masses
mass = {'H': 1.007825, 'C': 12.01, 'O': 15.9994, 'N': 14.0067, 'S': 31.972071, 
        'P': 30.973762}

def calculate_atomic_mass(molecule):
    """
    Calculate the atomic mass of a given molecule
    """
    mass = 0.0
    mol = molecule.split('-')

    for key in mass:
        if key in mol:
            atom = key

    return mass

print calculate_atomic_mass('H2-O')
print calculate_atomic_mass('H2-S-O4')
print calculate_atomic_mass('C2-H5-O-H')
print calculate_atomic_mass('H2-N-C6-H4-C-O-2H')

Solution:

Given all components have the shape Aa123, It might be easier here to identify parts with a regex, for example:

import re
srch = re.compile(r'([A-Za-z]+)(\d*)')
mass = {'H': 1.007825, 'C': 12.01, 'O': 15.9994, 'N': 14.0067, 'S': 31.972071, 'P': 30.973762}

def calculate_atomic_mass(molecule):
    return sum(mass[a[1]]*int(a[2] or '1') for a in srch.finditer(molecule))

Here our regular expression [wiki] thus captures a sequence of [A-Z-a-z]s, and a (possibly empty) sequence of digits (\d*), these are the first and second capture group respectively, and thus can be obtained for a match with a[1] and a[2].

this then yields:

>>> print(calculate_atomic_mass('H2-O'))
18.01505
>>> print(calculate_atomic_mass('H2-S-O4'))
97.985321
>>> print(calculate_atomic_mass('C2-H5-O-H'))
46.06635
>>> print(calculate_atomic_mass('H2-N-C6-H4-C-O-2H'))
121.130875
>>> print(calculate_atomic_mass('H2-N15-P3'))
305.037436

We thus take the sum of the mass[..] of the first capture group (the name of the atom) times the number at the end, and we use '1' in case no such number can be found.

Or we can first split the data, and then look for a atom part and a number part:

import re
srch = re.compile(r'^([A-Za-z]+)(\d*)$')

def calculate_atomic_mass(molecule):
    """
    Calculate the atomic mass of a given molecule
    """
    result = 0.0
    mol = molecule.split('-')
    if atm in mol:
        c = srch.find(atm)
        result += result[c[1]] * int(c[2] or '1')
    return result

Delete certain columns and add horizontally in AW. So many columns that I cannot type each one

I have been struggling more than a day and I cannot make my script work. Please help.

My txt file extends to 500 columns.

I need to delete columns 5,9,13,21,…, always delete n=4 column.

Then, after removing the columns I mentioned above, I need to add all the columns remaining, BUT NOT taking into account ONLY the column 1.
For this I am using:

awk '{print $1,$2+$3+.........}' >> comb.xvg

The thing is that don’t want to go manually adding until I reach 500.

My final document should have only two columns.

  • The first from the very beginning
  • And the another column that has the sum of all the other ones (please be aware that I am adding horizontally and not vertically).
    The sum is done horizontally from column 2 to the column 500.

Could someone please help me to do this? I have tried different sets using for loop but they fail.

I am new at this and also using stack. Please my apologies if I am not fully clear but I cannot upload pics.

Thanks.

Solution:

awk to the rescue!

this script will sum up the columns 2,3,4, 6,7,8, 10,.. (that is skipping 5,9,…4k+1…)

awk '{sum=0; for(i=2;i<=NF;i++) sum+=(i-1)%4?$i:0; print $1,sum}'

Explanation
We’re summing up the elements in the row. If we were to add them all, sum+=$i would do, however you want to skip the values at indices 2k+1, so we use the ternary operator v=c?a:b, that is if(c) v=a; else v=b. (i-1)%4 is the modulus by 4, will be zero for i=5,9,…,2k+1.

deleting the columns doesn’t seem to be necessary since you’re not printing the resulting panel.

to test

$ seq 20 | xargs -n 10 | awk ...

prints 

1 40
11 110

to verify: sum(2+3+…+10) = 54, so after removing 5 and 9, you’ll get 40. For sum(12+13+…+20) it’s 10 more for each element, i.e. 40+7*10=110.

Follow up question: How to add s2=2,6,10…; s3=3,7,11…; s4=4,8,12…

awk '{s2=s3=s4=0; 
      for(i=2;i<=NF;i+=4) 
        {s2+=$i; s3+=$(i+1); s4+=$(i+2)}; 
      print $1, s2, s3, s4}'

How to iterate through two lists with iter() and yield?

A simple example:

 popen = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True, shell=True)
 for stdout_line in iter(popen.stdout.readline, ""): # how to add popen.stderr.readline check?
     yield stdout_line

We read from popen.stdout, yet we also want to read from stderr at the same time! We do not know when process will end.

So How to iterate through two lists with iter() and yield?

Solution:

These aren’t lists, and the right way to work with them isn’t how you would work with lists. If you want to stuff a process’s stdout and stderr into one combined stream, do that with output redirection:

from subprocess import PIPE, STDOUT

process = subprocess.Popen(cmd, stdout=PIPE, stderr=STDOUT, ...)
#                                                   ^^^^^^

String without quotes within a string (python)

I’m trying to write text to file, but I have other text I need to include besides the targeted string. When I’m looping over the targeted strings it is printed with quotes as the quotes are needed for other text.
How to remove quotes from a string that I’m inserting each loop?

list=['random', 'stuff', 1]
with open(textfile, 'a') as txtfile:
    for item in list:
        print("""Need to have stuff before %a and after each loop string"""  
        %item, file=txtfile)

Output: Need to have stuff before ‘random’ and after each loop string;
Wanted output: Need to have stuff before random and after each loop string

Solution:

You can use str.format:

>>> li=['random', 'stuff', 1]
>>> for item in li:
...    print("before {} after".format(item))
... 
before random after
before stuff after
before 1 after

Or you can use %s with the % operator:

>>> for item in li:
...    print("before %s after" % item)
... 
before random after
before stuff after
before 1 after

(And don’t call a list list or you will overwrite the Python function of the same name…)

python: return False if there is not an element in a list starting with 'p='

having a list like

lst = ['hello', 'stack', 'overflow', 'friends']

how can i do something like:

if there is not an element in lst starting with 'p=' return False else return True

?

i was thinking something like:

for i in lst:
   if i.startswith('p=')
       return True

but i can’t add the return False inside the loop or it goes out at the first element.

Solution:

This will make a list of whether or not each element of lst satisfies your condition, then computes the or of those results:

any([x.startswith("p=") for x in lst])

Loop until choice within list

I am trying to write a script which loops until the user chooses a value within a list (single digit numbers from 0 to 9). This is my .sh script which I try to run in the ubuntu 16.04 shell using the sh command:

choice=999
echo $choice
until [[ $choice in 0 1 2 3 4 5 6 7 8 9 ]]
do
  read -p "How many would you like to add? " choice
done

No matter what I do, I just can’t get it to work. Here’s a test, to give you an idea of the errors at hand:

sh test2.sh
999
test2.sh: 3: test2.sh: [[: not found
How many would you like to add? f
test2.sh: 3: test2.sh: [[: not found
How many would you like to add? 2
test2.sh: 3: test2.sh: [[: not found
How many would you like to add? 3
test2.sh: 3: test2.sh: [[: not found
How many would you like to add? r
test2.sh: 3: test2.sh: [[: not found

I’ve tried so many things:

  • Avoiding until and using while
  • Using just singular square brackets [ condition ], or no brackets at all
  • Using =~ to match the regular expression ^[0-9]

Nothing works. Always that same error. What’s going on? 😦

Solution:

Firstly, your [[: not found suggests that you’re not using Bash. Either add a #!/bin/bash at the top of your script, or run it with bash test2.sh, or use the standard [.

Either way, you can’t use in like that. One alternative would be to use a case statement:

while :; do
  read -p "How many would you like to add? " choice
  case $choice in
    [0-9])
      break
      ;;
  esac
done

The nice thing about case statements is that they allow you to use glob patterns, so [0-9] matches any number from 0 to 9.

If you are planning on using Bash in the end, you can also go for something like this:

#!/bin/bash

until [[ $choice =~ ^[0-9]$ ]]; do
  read -p "How many would you like to add? " choice
done

Here, a regular expression is used to match a since digit from 0 to 9.

add a loop chaining method in java

I have a program that runs chaining methods

MyObject o = MyObject.getInstance().method1().method2().go();

Now, this instance returns multiple lines of data,

I can execute them in a loop but I would rather do this:

MyObject o = MyObject.getInstance().foreach().method1().method2().go();

I.e used a for each

is it possible in Java to do this?

Solution:

You can do this in Java 8, assuming getInstance() returns a stream:

MyObject.getInstance().forEach(item-> item.method1().method2().go() );

See the streaming API documentation here: https://docs.oracle.com/javase/tutorial/collections/streams/

java – variable inside of loop

I have just start learning java and I’m sorry if my question is a bit nooby.

Can anyone tell me why this code gives an Error and how to fix it?
thanks

static String test = "abc";
static String lower = "abcdefghijklmnopqrstuvwxyz" ;
static String re = "" ;
public static void main(String[] args) {
    for (int i = 0 ; i < test.length() ; ++i ) {
        char x = test.charAt(i);
        int f = lower.indexOf(x);
        int h = (f + 2) %26;
        if (h <0) {
            h = h + 26;
        }
        char r = lower.charAt(h);
        String re = re +  r ;       /* here is the problem */

    }

    System.out.println(re);
    }
}

output: The local variable re may not have been initialized

Solution:

The problem is that you are re-declaring your re variable as a local variable, “shadowing” the static String re field declared outside of main.

In general, it is not a good idea to make mutable static fields, so you should move the declaration of String re = "" inside main(), and replace String re = re + r ; declaration with re += r.

Note: Although the above will get your code to work, it is not a good idea to append to a String variable inside a loop. You would be better off using a StringBuilder object, and calling its append method inside the loop:

StringBuilder re = new StringBuilder();
for (...) {
    ...
    re.append(r);
}

Ansible cheat sheet

Configuration file

intro_configuration.html

First one found from of

  • Contents of $ANSIBLE_CONFIG
  • ./ansible.cfg
  • ~/.ansible.cfg
  • /etc/ansible/ansible.cfg

Configuration settings can be overridden by environment variables – see constants.py in the source tree for names.

Patterns

intro_patterns.html

Used on the ansible command line, or in playbooks.

  • all (or *)
  • hostname: foo.example.com
  • groupname: webservers
  • or: webservers:dbserver
  • exclude: webserver:!phoenix
  • intersection: webservers:&staging

Operators can be chained: webservers:dbservers:&staging:!phoenix

Patterns can include variable substitutions: {{foo}}, wildcards: *.example.com or 192.168.1.*, and regular expressions: ~(web|db).*\.example\.com

Inventory files

intro_inventory.html, intro_dynamic_inventory.html

‘INI-file’ structure, blocks define groups. Hosts allowed in more than one group. Non-standard SSH port can follow hostname separated by ‘:’ (but see also ansible_ssh_port below).

Hostname ranges: www[01:50].example.com, db-[a:f].example.com

Per-host variables: foo.example.com foo=bar baz=wibble

  • [foo:children]: new group foo containing all members if included groups
  • [foo:vars]: variable definitions for all members of group foo

Inventory file defaults to /etc/ansible/hosts. Veritable with -i or in the configuration file. The ‘file’ can also be a dynamic inventory script. If a directory, all contained files are processed.

Variable files:

intro_inventory.html

YAML; given inventory file at ./hosts:

  • ./group_vars/foo: variable definitions for all members of group foo
  • ./host_vars/foo.example.com: variable definitions for foo.example.com

group_vars and host_vars directories can also exist in the playbook directory. If both paths exist, variables in the playbook directory will be loaded second.

Behavioral inventory parameters:

intro_inventory.html

  • ansible_ssh_host
  • ansible_ssh_port
  • ansible_ssh_user
  • ansible_ssh_pass
  • ansible_sudo_pass
  • ansible_connection
  • ansible_ssh_private_key_file
  • ansible_python_interpreter
  • ansible_*_interpreter

Playbooks

playbooks_intro.html, playbooks_roles.html

Playbooks are a YAML list of one or more plays. Most (all?) keys are optional. Lines can be broken on space with continuation lines indented.

Playbooks consist of a list of one or more ‘plays’ and/or inclusions:

---
- include: playbook.yml
- <play>
- ...

Plays

playbooks_intro.html, playbooks_roles.html, playbooks_variables.html, playbooks_conditionals.html,playbooks_acceleration.html, playbooks_delegation.html, playbooks_prompts.html, playbooks_tags.html Forum postingForum postinb

Plays consist of play metadata and a sequence of task and handler definitions, and roles.

- hosts: webservers
  remote_user: root
  sudo: yes
  sudo_user: postgress
  su: yes
  su_user: exim
  gather_facts: no
  accelerate: no
  accelerate_port: 5099
  any_errors_fatal: yes
  max_fail_percentage: 30
  connection: local
  serial: 5
  vars:
    http_port: 80
  vars_files:
    - "vars.yml"
    - [ "try-first.yml", "try-second-.yml" ]
  vars_prompt:
    - name: "my_password2"
      prompt: "Enter password2"
      default: "secret"
      private: yes
      encrypt: "md5_crypt"
      confirm: yes
      salt: 1234
      salt_size: 8
  tags: 
    - stuff
    - nonsence
  pre_tasks:
    - <task>
    - ...
  roles:
    - common
    - { role: common, port: 5000, when: "bar == 'Baz'", tags :[one, two] }
    - { role: common, when: month == 'Jan' }
    - ...
  tasks:
    - include: tasks.yaml
    - include: tasks.yaml foo=bar baz=wibble
    - include: tasks.yaml
      vars:
        foo: aaa 
        baz:
          - z
          - y
    - { include: tasks.yaml, foo: zzz, baz: [a,b]}
    - include: tasks.yaml
      when: day == 'Thursday'
    - <task>
    - ...
  post_tasks:
    - <task>
    - ...
  handlers:
    - include: handlers.yml
    - <task>
    - ...

Using encrypt with vars_prompt requires that Passlib is installed.

In addition the source code implies the availability of the following which don’t seem to be mentioned in the documentation: name, user (deprecated), port, accelerate_ipv6, role_names, and vault_password.

Task definitions

playbooks_intro.html, playbooks_roles.html, playbooks_async.html, playbooks_checkmode.html, playbooks_delegation.html,playbooks_environment.html, playbooks_error_handling.html, playbooks_tags.html ansible-1-5-released Forum postingAnsible examples

Each task definition is a list of items, normally including at least a name and a module invocation:

- name: task
  remote_user: apache
  sudo: yes
  sudo_user: postgress
  sudo_pass: wibble
  su: yes
  su_user: exim
  ignore_errors: True
  delegate_to: 127.0.0.1
  async: 45
  poll: 5
  always_run: no
  run_once: false
  meta: flush_handlers
  no_log: true
  environment: <hash>
  environment:
    var1: val1
    var2: val2
  tags: 
    - stuff
    - nonsence
  <module>: src=template.j2 dest=/etc/foo.conf
  action: <module>, src=template.j2 dest=/etc/foo.conf
  action: <module>
  args:
      src=template.j2
      dest=/etc/foo.conf
  local_action: <module> /usr/bin/take_out_of_pool {{ inventory_hostname }}
  when: ansible_os_family == "Debian"
  register: result
  failed_when: "'FAILED' in result.stderr"
  changed_when: result.rc != 2
  notify:
    - restart apache

delegate_to: 127.0.0.1 is implied by local_action:

The forms <module>: <args>, action: <module> <args>, and local_action: <module> <args> are mutually-exclusive.

Additional keys when_*, until, retries and delay are documented below under ‘Loops’.

In addition the source code implies the availability of the following which don’t seem to be mentioned in the documentation:first_available_file (deprecated), transport, connection, any_errors_fatal.

Roles

playbooks_roles.html

Directory structure:

playbook.yml
roles/
   common/
     tasks/
       main.yml
     handlers/
       main.yml
     vars/
       main.yml
     meta/
       main.yml
     defaults/
       main.yml
     files/
     templates/
     library/

Modules

modules.htm, modules_by_category.html

List all installed modules with

ansible-doc --list

Document a particular module with

ansible-doc <module>

Show playbook snippet for specified module

ansible-doc -i <module>

Variables

playbooks_roles.html, playbooks_variables.html

Names: letters, digits, underscores; starting with a letter.

Substitution examples:

  • {{ var }}
  • {{ var["key1"]["key2"]}}
  • {{ var.key1.key2 }}
  • {{ list[0] }}

YAML requires an item starting with a variable substitution to be quoted.

Sources:

  • Highest priority:
    • --extra-vars on the command line
  • General:
    • vars component of a playbook
    • From files referenced by vars_file in a playbook
    • From included files (incl. roles)
    • Parameters passed to includes
    • register: in tasks
  • Lower priority:
    • Inventory (set on host or group)
  • Lower priority:
    • Facts (see below)
    • Any /etc/ansible/facts.d/filename.fact on managed machines (sets variables with `ansible_local.filename. prefix)
  • Lowest priority
    • Role defaults (from defaults/main.yml)

Built-in:

  • hostvars (e.g. hostvars[other.example.com][...])
  • group_names (groups containing current host)
  • groups (all groups and hosts in the inventory)
  • inventory_hostname (current host as in inventory)
  • inventory_hostname_short (first component of inventory_hostname)
  • play_hosts (hostnames in scope for current play)
  • inventory_dir (location of the inventory)
  • inventoty_file (name of the inventory)

Facts:

Run ansible hostname -m setup, but in particular:

  • ansible_distribution
  • ansible_distribution_release
  • ansible_distribution_version
  • ansible_fqdn
  • ansible_hostname
  • ansible_os_family
  • ansible_pkg_mgr
  • ansible_default_ipv4.address
  • ansible_default_ipv6.address

Content of ‘registered’ variables:

playbooks_conditionals.html, playbooks_loops.html

Depends on module. Typically includes:

  • .rc
  • .stdout
  • .stdout_lines
  • .changed
  • .msg (following failure)
  • .results (when used in a loop)

See also failed, changed, etc filters.

When used in a loop the result element is a list containing all responses from the module.

Additionally available in templates:

  • ansible_managed: string containing the information below
  • template_host: node name of the templateâ��s machine
  • template_uid: the owner
  • template_path: absolute path of the template
  • template_fullpath: the absolute path of the template
  • template_run_date: the date that the template was rendered

Filters

playbooks_variables.html

  • {{ var | to_nice_json }}
  • {{ var | to_json }}
  • {{ var | from_json }}
  • {{ var | to_nice_yml }}
  • {{ var | to_yml }}
  • {{ var | from_yml }}
  • {{ result | failed }}
  • {{ result | changed }}
  • {{ result | success }}
  • {{ result | skipped }}
  • {{ var | manditory }}
  • {{ var | default(5) }}
  • {{ list1 | unique }}
  • {{ list1 | union(list2) }}
  • {{ list1 | intersect(list2) }}
  • {{ list1 | difference(list2) }}
  • {{ list1 | symmetric_difference(list2) }}
  • {{ ver1 | version_compare(ver2, operator='>=', strict=True }}
  • {{ list | random }}
  • {{ number | random }}
  • {{ number | random(start=1, step=10) }}
  • {{ list | join(" ") }}
  • {{ path | basename }}
  • {{ path | dirname }}
  • {{ path | expanduser }}
  • {{ path | realpath }}
  • {{ var | b64decode }}
  • {{ var | b64encode }}
  • {{ filename | md5 }}
  • {{ var | bool }}
  • {{ var | int }}
  • {{ var | quote }}
  • {{ var | md5 }}
  • {{ var | fileglob }}
  • {{ var | match }}
  • {{ var | search }}
  • {{ var | regex }}
  • {{ var | regexp_replace('from', 'to' )}}

See also default jinja2 filters. In YAML, values starting { must be quoted.

Lookups

playbooks_lookups.html

Lookups are evaluated on the control machine.

  • {{ lookup('file', '/etc/foo.txt') }}
  • {{ lookup('password', '/tmp/passwordfile length=20 chars=ascii_letters,digits') }}
  • {{ lookup('env','HOME') }}
  • {{ lookup('pipe','date') }}
  • {{ lookup('redis_kv', 'redis://localhost:6379,somekey') }}
  • {{ lookup('dnstxt', 'example.com') }}
  • {{ lookup('template', './some_template.j2') }}

Lookups can be assigned to variables and will be evaluated each time the variable is used.

Lookup plugins also support loop iteration (see below).

Conditions

playbooks_conditionals.html

when: <condition>, where condition is:

  • var == "Vaue", var >= 5, etc.
  • var, where var coreces to boolean (yes, true, True, TRUE)
  • var is defined, var is not defined
  • <condition1> and <condition2> (also or?)

Combined with with_items, the when statement is processed for each item.

when can also be applied to includes and roles. Conditional Imports and variable substitution in file and template names can avoid the need for explicit conditionals.

Loops

playbooks_loops.html

In addition the source code implies the availability of the following which don’t seem to be mentioned in the documentation: csvfile, etcd, inventory_hostname.

Standard:

- user: name={{ item }} state=present groups=wheel
  with_items:
    - testuser1
    - testuser2
   
- name: add several users
  user: name={{ item.name }} state=present groups={{ item.groups }}
  with_items:
    - { name: 'testuser1', groups: 'wheel' }
    - { name: 'testuser2', groups: 'root' }

  with_items: somelist

Nested:

- mysql_user: name={{ item[0] }} priv={{ item[1] }}.*:ALL                
                           append_privs=yes password=foo
  with_nested:
    - [ 'alice', 'bob', 'eve' ]
    - [ 'clientdb', 'employeedb', 'providerdb' ]

Over hashes:

Given

---
users:
  alice:
    name: Alice Appleworth
    telephone: 123-456-7890
  bob:
    name: Bob Bananarama
    telephone: 987-654-3210
    
tasks:
  - name: Print phone records
    debug: msg="User {{ item.key }} is {{ item.value.name }} 
                     ({{ item.value.telephone }})"
    with_dict: users

Fileglob:

- copy: src={{ item }} dest=/etc/fooapp/ owner=root mode=600
  with_fileglob:
    - /playbooks/files/fooapp/*

In a role, relative paths resolve relative to the roles/<rolename>/files directory.

With content of file:

(see example for authorized_key module)

- authorized_key: user=deploy key="{{ item }}"
  with_file:
    - public_keys/doe-jane
    - public_keys/doe-john

See also the file lookup when the content of a file is needed.

Parallel sets of data:

Given

---
alpha: [ 'a', 'b', 'c', 'd' ]
numbers:  [ 1, 2, 3, 4 ]

- debug: msg="{{ item.0 }} and {{ item.1 }}"
  with_together:
    - alpha
    - numbers

Subelements:

Given

---
users:
  - name: alice
    authorized:
      - /tmp/alice/onekey.pub
      - /tmp/alice/twokey.pub
  - name: bob
    authorized:
      - /tmp/bob/id_rsa.pub

- authorized_key: "user={{ item.0.name }} 
                   key='{{ lookup('file', item.1) }}'"
  with_subelements:
     - users
     - authorized

Integer sequence:

Decimal, hexadecimal (0x3f8) or octal (0600)

- user: name={{ item }} state=present groups=evens
  with_sequence: start=0 end=32 format=testuser%02x
      
  with_sequence: start=4 end=16 stride=2
      
  with_sequence: count=4

Random choice:

- debug: msg={{ item }}
  with_random_choice:
     - "go through the door"
     - "drink from the goblet"
     - "press the red button"
     - "do nothing"

Do-Until:

- action: shell /usr/bin/foo
  register: result
  until: result.stdout.find("all systems go") != -1
  retries: 5
  delay: 10

Results of a local program:

- name: Example of looping over a command result
  shell: /usr/bin/frobnicate {{ item }}
  with_lines: /usr/bin/frobnications_per_host 
                       --param {{ inventory_hostname }}

To loop over the results of a remote program, use register: result and then with_items: result.stdout_lines in a subsequent task.

Indexed list:

- name: indexed loop demo
  debug: msg="at array position {{ item.0 }} there is 
                                     a value {{ item.1 }}"
  with_indexed_items: some_list

Flattened list:

---
# file: roles/foo/vars/main.yml
packages_base:
  - [ 'foo-package', 'bar-package' ]
packages_apps:
  - [ ['one-package', 'two-package' ]]
  - [ ['red-package'], ['blue-package']]
  
- name: flattened loop demo
  yum: name={{ item }} state=installed
  with_flattened:
    - packages_base
    - packages_apps

First found:

- name: template a file
  template: src={{ item }} dest=/etc/myapp/foo.conf
  with_first_found:
    - files:
        - {{ ansible_distribution }}.conf
        - default.conf
      paths:
         - search_location_one/somedir/
         - /opt/other_location/somedir/

Tags

Both plays and tasks support a tags: attribute.

- template: src=templates/src.j2 dest=/etc/foo.conf
  tags:
    - configuration

Tags can be applied to roles and includes (effectively tagging all included tasks)

roles:
    - { role: webserver, port: 5000, tags: [ 'web', 'foo' ] }

- include: foo.yml tags=web,foo

To select by tag:

ansible-playbook example.yml --tags "configuration,packages"
ansible-playbook example.yml --skip-tags "notification"

Command lines

ansible

Usage: ansible <host-pattern> [options]

Options:
  -a MODULE_ARGS, --args=MODULE_ARGS
                        module arguments
  -k, --ask-pass        ask for SSH password
  --ask-su-pass         ask for su password
  -K, --ask-sudo-pass   ask for sudo password
  --ask-vault-pass      ask for vault password
  -B SECONDS, --background=SECONDS
                        run asynchronously, failing after X seconds
                        (default=N/A)
  -C, --check           don't make any changes; instead, try to predict some
                        of the changes that may occur
  -c CONNECTION, --connection=CONNECTION
                        connection type to use (default=smart)
  -f FORKS, --forks=FORKS
                        specify number of parallel processes to use
                        (default=5)
  -h, --help            show this help message and exit
  -i INVENTORY, --inventory-file=INVENTORY
                        specify inventory host file
                        (default=/etc/ansible/hosts)
  -l SUBSET, --limit=SUBSET
                        further limit selected hosts to an additional pattern
  --list-hosts          outputs a list of matching hosts; does not execute
                        anything else
  -m MODULE_NAME, --module-name=MODULE_NAME
                        module name to execute (default=command)
  -M MODULE_PATH, --module-path=MODULE_PATH
                        specify path(s) to module library
                        (default=/usr/share/ansible)
  -o, --one-line        condense output
  -P POLL_INTERVAL, --poll=POLL_INTERVAL
                        set the poll interval if using -B (default=15)
  --private-key=PRIVATE_KEY_FILE
                        use this file to authenticate the connection
  -S, --su              run operations with su
  -R SU_USER, --su-user=SU_USER
                        run operations with su as this user (default=root)
  -s, --sudo            run operations with sudo (nopasswd)
  -U SUDO_USER, --sudo-user=SUDO_USER
                        desired sudo user (default=root)
  -T TIMEOUT, --timeout=TIMEOUT
                        override the SSH timeout in seconds (default=10)
  -t TREE, --tree=TREE  log output to this directory
  -u REMOTE_USER, --user=REMOTE_USER
                        connect as this user (default=jw35)
  --vault-password-file=VAULT_PASSWORD_FILE
                        vault password file
  -v, --verbose         verbose mode (-vvv for more, -vvvv to enable
                        connection debugging)
  --version             show program's version number and exit

ansible-playbook

Usage: ansible-playbook playbook.yml

Options:
  -k, --ask-pass        ask for SSH password
  --ask-su-pass         ask for su password
  -K, --ask-sudo-pass   ask for sudo password
  --ask-vault-pass      ask for vault password
  -C, --check           don't make any changes; instead, try to predict some
                        of the changes that may occur
  -c CONNECTION, --connection=CONNECTION
                        connection type to use (default=smart)
  -D, --diff            when changing (small) files and templates, show the
                        differences in those files; works great with --check
  -e EXTRA_VARS, --extra-vars=EXTRA_VARS
                        set additional variables as key=value or YAML/JSON
  -f FORKS, --forks=FORKS
                        specify number of parallel processes to use
                        (default=5)
  -h, --help            show this help message and exit
  -i INVENTORY, --inventory-file=INVENTORY
                        specify inventory host file
                        (default=/etc/ansible/hosts)
  -l SUBSET, --limit=SUBSET
                        further limit selected hosts to an additional pattern
  --list-hosts          outputs a list of matching hosts; does not execute
                        anything else
  --list-tasks          list all tasks that would be executed
  -M MODULE_PATH, --module-path=MODULE_PATH
                        specify path(s) to module library
                        (default=/usr/share/ansible)
  --private-key=PRIVATE_KEY_FILE
                        use this file to authenticate the connection
  --skip-tags=SKIP_TAGS
                        only run plays and tasks whose tags do not match these
                        values
  --start-at-task=START_AT
                        start the playbook at the task matching this name
  --step                one-step-at-a-time: confirm each task before running
  -S, --su              run operations with su
  -R SU_USER, --su-user=SU_USER
                        run operations with su as this user (default=root)
  -s, --sudo            run operations with sudo (nopasswd)
  -U SUDO_USER, --sudo-user=SUDO_USER
                        desired sudo user (default=root)
  --syntax-check        perform a syntax check on the playbook, but do not
                        execute it
  -t TAGS, --tags=TAGS  only run plays and tasks tagged with these values
  -T TIMEOUT, --timeout=TIMEOUT
                        override the SSH timeout in seconds (default=10)
  -u REMOTE_USER, --user=REMOTE_USER
                        connect as this user (default=jw35)
  --vault-password-file=VAULT_PASSWORD_FILE
                        vault password file
  -v, --verbose         verbose mode (-vvv for more, -vvvv to enable
                        connection debugging)
  --version             show program's version number and exit

ansible-vault

playbooks_vault.html

Usage: ansible-vault [create|decrypt|edit|encrypt|rekey] [--help] [options] file_name

Options:
  -h, --help  show this help message and exit

See 'ansible-vault <command> --help' for more information on a specific command.

ansible-doc

Usage: ansible-doc [options] [module...]

Show Ansible module documentation

Options:
  --version             show program's version number and exit
  -h, --help            show this help message and exit
  -M MODULE_PATH, --module-path=MODULE_PATH
                             Ansible modules/ directory
  -l, --list            List available modules
  -s, --snippet         Show playbook snippet for specified module(s)
  -v                    Show version number and exit

ansible-galaxy

Usage: ansible-galaxy [init|info|install|list|remove] [--help] [options] ...

Options:
  -h, --help  show this help message and exit

  See 'ansible-galaxy <command> --help' for more information on a
  specific command

ansible-pull

Usage: ansible-pull [options] [playbook.yml]