envsubst

envsubst

GNU envsubst: substitutes environment variables in shell templates.

curl -fsSL https://unflab.app/get | sh -s -- envsubst

Installs to ~/.local/bin. Add --prefix /usr/local/bin to
put it somewhere else, or --uninstall to remove it.

Why it’s here

One binary out of a much larger suite.

Details

Built from that exact tarball, with its SHA-256 pinned in the
recipe. The binary links against nothing outside /usr/lib
and /System/, checked in CI before release.

GNU envsubst: substitutes environment variables in shell templates.

macOS ships no envsubst at all, so this is the usual way to get one
without installing a localisation library to go with it.

# Substitute every variable that is set
export NAME=world PORT=8080
echo 'hello $NAME on port $PORT' | envsubst

# Substitute only the named ones, leaving the rest alone
envsubst '$NAME' < template.conf > out.conf

That second form is the useful one for config templating: anything not
named is passed through untouched, so a file full of $ syntax meant
for some other tool survives intact. Variables that are named but
unset expand to nothing.

envsubst --variables '$A $B' lists the variables a template references,
which is handy for checking nothing is missing before substituting.

man envsubst has the rest.

Install

./install.sh                      # into ~/.local/bin
./install.sh --prefix /usr/local/bin
./install.sh --uninstall

About this build

brew install gettext builds the whole GNU gettext project — 22
executables, libintl, libasprintf, libtextstyle, Emacs Lisp files
and the manual, against json-c and libunistring — to give you this one
93 KB binary. Homebrew’s formula is really there as a library: dozens
of other formulae depend on it for libintl, and envsubst comes along
as a side effect.

This is just envsubst, built from gettext’s gettext-runtime
subdirectory, which upstream’s own PACKAGING file describes as
“utilities for sh programs” and recommends splitting out. Configured
--disable-nls, it links libSystem and nothing else, so there is
nothing further to install.

The rest of gettext is not packaged here. The other runtime programs
(gettext, ngettext, printf_gettext, printf_ngettext) translate
strings via .mo message catalogues, and nothing on a Mac installs
catalogues where they would be found — they would mostly echo their
arguments back. The developer tools (msgfmt, msgmerge, xgettext
and the rest) are a much larger build needing libunistring and libxml2,
and serve translators rather than shell users.

Upstream

• Home: https://www.gnu.org/software/gettext/
• Version: 1.0
• Licence: GPL-3.0-or-later (see LICENSE)

GNU gettext is the Free Software Foundation’s work. unflab only compiles
and packages it.