sempl

Stupid simple bash templating.

Uses environment variables, inherited or sourced from a file, to render templates using common bash utilities.

Given the following template (examples/config.yaml.tmpl):

user: $USER
password: ${password:-defaultpass}
files:
  ### begin
  # for f in $(ls); do
  - $f
  # done
  ### end

We could expect the following output when running sempl:

$ USER=myuser sempl -o examples/config.yaml.tmpl
user: myuser
password: defaultpass
files:
  - README.md
  - examples
  - sempl

Installation

curl -L -o sempl https://github.com/nextrevision/sempl/raw/master/sempl
chmod +x sempl

Requirements

• bash
• sed (GNU)
• mktemp
• grep (egrep)
• openssl (if using encryption)

Usage

usage: ./sempl [args] template [outfile]

args:
-s [varsfile]   vars file (can be repeated)
-p [password]   decryption password
-k [passfile]   decryption password file
-v              verbose
-o              print template to stdout
-f              fail if a variable is unset with no default
-c              check that the template will render, but do not write the file
-h              help
--version       print version and exit
--update        update script to latest version

Loops

It is possible to use inline bash loops for more complex logic.

In order to designate where the loop should start, you must have in text ### begin followed at some point by ### end signaling the end of a loop. Any code you wish to execute must be preceded with a # and a space. Anything without a preceding # will be rendered as output by the template.

Caveats

• A backslash must be doubly escaped (i.e. \\)
• Redirection in command substitution does not work (i.e. $(cat blah 2>&1))
• Quotes (single and double) must be closed or escaped

Examples

Template Expansion w/ Environment Vars

source examples/vars.sh
./sempl -v examples/config.json.tmpl

Template Expansion w/ Vars File

./sempl -v -s examples/vars.sh examples/config.json.tmpl

Template Expansion w/ Outfile

./sempl -v -s examples/vars.sh examples/config.json.tmpl \
  examples/outfile.json

Template Expansion w/ Decryption Key

./sempl -v -p mypassword -s examples/vars.sh.enc \
  examples/config.json.tmpl examples/outfile.json

Template Expansion w/ Decryption File

./sempl -v -k examples/passfile.txt -s examples/vars.sh.enc \
  examples/outfile.json examples/config.json.tmpl

Template Expansion w/ Multiple Varsfiles

Multiple vars files can be specified by repeating the -s flag. Vars files can either be passed either encrypted or decrypted.

./sempl -v -p mypassword -s examples/vars.sh.enc \
  -s examples/vars.sh -s examples/vars.sh \
  examples/config.json.tmpl examples/outfile.json

Looping over a list of files

Given the template test.txt.tmpl below:

This is a text file. Siblings include:
### begin
# for i in $(ls); do
# if [[ $i == "sibling1.txt" ]]; then
  $i (favorite)
# else
  $i
# fi
# done
### end

Could be rendered as:

This is a text file. Siblings include:
  test.txt.tmpl
  sibling1.txt (favorite)
  sibling2.txt

Encryption

crypttool is a very simple wrapper around the openssl command that can encrypt, decrypt, or edit a file. sempl can take an encrypted file and decrypt it at runtime with a password/passfile specified as an argument. This allows storing of secrets in variable files and decryption at the point of rendering a template file.

Encrypting a Varsfile

./crypttool -p mypassword encrypt examples/vars.sh

Decrypting a Varsfile

./crypttool -p mypassword decrypt examples/vars.sh.enc

Editing an Encrypted Varsfile

./crypttool -p mypassword edit examples/vars.sh.enc