malud/temgo

Environment variable based template engine like Jinja2 for your container config files. Lightweight, fast, go cli

temgo's Issues

inline editing

tg is a nice replacement for sed when moving ENV vars to config files in docker entrypoint scripts!

however, the tg < template > file semantics forces me to use a separate template file. to keep things easy to read, i would prefer an inline editing mode like sed -i:

tg -i my.conf

the command should be idempotent to avoid changes to the file when the docker container is restarted. ideally, subsequent runs would not write the file at all (because no placeholder was found).

no output without placeholders

When the input stream has no placeholders, tg generates no output:

Expected:

$ echo foo bar | ./tg
foo bar

Actual:

$ echo foo bar | ./tg

With correct placeholders, it works as expected:

$ echo 'foo {{ x }}bar' | ./tg
foo bar

However, incomplete placeholders show the erroneous behaviour, too:

$ echo 'foo {{ }}bar' | ./tg
$ echo 'foo {{x}}bar' | ./tg
$ echo 'foo {{x }}bar' | ./tg

Feature Request: strict mode – fail on missing vars

I want to propose a strict mode that makes tg fail if a placeholder cannot be replaced.

$ echo '{{ NOT_SET }}' | tg -s
Error: placeholder NOT_SET cannot be replaced
$ echo $?
1

My use case is as usual a docker container's entrypoint. I use tg to fill env vars into configuration files. The configuration file may be broken if a placeholder is not replaced. In the entrypoint I have to check that every env variable used in placeholders is set. This is error prone, because I have at least two places to get it wrong.

With tg -s I would be able to let my set -e entrypoint fail without repeating the variable list.

The stdout variant tg -s > file will empty the file because bash opens the redirection before the command is executed.

But in inplace mode tg -s -i file the output file should not be written at all, if a variable is missing.

Feature Request: Default Values

I would like to define default values for replacements:

KEY={{ VALUE : default }}

especially for docker setups, where tg is used from the entrypoint, I imagine this to be more robust than defining all necessary env vars in docker-compose.yml. this would also eliminate the need to check for all variables from the tg called (entrypoint).

The other nice effect is, that default values can be defined in the target file.

Jinja defaults are quite cumbersome: {{ first_name|default("walter", true) }. therefore my proposal is more bash-oriented, where a default can be written as ${NAME:-walter}. the colon could have arbitrary whitespaces (see above) or we could define {{ VALUE:default }}. it doesn't really matter.

However, it would be handy to allow whitespaces in the default value without the need for quoting:

TITLE={{ PAGE_TITLE : Good news! }}

For processing I would suggest to read everything behind the colon and trim whitespaces.

@malud, what do you think?

Feature request: Make temgo fail if a variable is not set

This feature would be quite useful for saving a lot of code (depends on the number of variables). Currently I do something like this:

set -o errexit
set -o unset

[[ -z ${HTTP_SERVER} ]] && :
[[ -z ${HTTPS_SERVER} ]] && :
[[ -z ${DB_HOSTNAME} ]] && :
[[ -z ${DB_USERNAME} ]] && :
[[ -z ${DB_PASSWORD} ]] && :
[[ -z ${DB_DATABASE} ]] && :
[[ -z ${DB_PORT} ]] && :
[[ -z ${DB_PREFIX} ]] && :
[[ -z ${ADMIN_HTTP_SERVER} ]] && :
[[ -z ${ADMIN_HTTP_CATALOG} ]] && :
[[ -z ${ADMIN_HTTPS_SERVER} ]] && :
[[ -z ${ADMIN_HTTPS_CATALOG} ]] && :

tg -i /app/config.php

If temgo failed when a variable is not set, let's say with the -f switch (force/fail), the above would look like this:

set -o errexit
tg -f -i /app/config.php

The savings on nerves and typing would be enormous ;)

Cheers

Parse error for environment values containing equals rune

The os envs are parsed naively with a strings.Split("=") which leads to wrong value replacements for e.g. a URI with query params.

The Env value https://example.com/?query=param gets mapped to [key]=https://example.com/?query".