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