https://github.com/sgreben/subst
substitutes $variables in text. single binary, no dependencies. linux, osx, windows.
https://github.com/sgreben/subst
envsubst simpler stdin stdout substitution variables
Last synced: 30 days ago
JSON representation
substitutes $variables in text. single binary, no dependencies. linux, osx, windows.
- Host: GitHub
- URL: https://github.com/sgreben/subst
- Owner: sgreben
- License: mit
- Created: 2018-04-16T13:31:47.000Z (about 7 years ago)
- Default Branch: master
- Last Pushed: 2019-02-15T09:41:56.000Z (over 6 years ago)
- Last Synced: 2025-03-31T04:02:54.901Z (2 months ago)
- Topics: envsubst, simpler, stdin, stdout, substitution, variables
- Language: Go
- Homepage:
- Size: 64.5 KB
- Stars: 14
- Watchers: 2
- Forks: 0
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# subst - substitute $variables in text
`subst` parses its arguments as `KEY=VALUE` pairs, substitutes `$KEY`s by `VALUE`s in stdin, and writes the result to stdout.
- [Get it](#get-it)
- [Use it](#use-it)
- [Examples](#examples)
- [Comments](#comments)
## Get it
Using go get:
```bash
go get -u github.com/sgreben/subst
```
Or [download the binary](https://github.com/sgreben/subst/releases/latest) from the releases page.
```bash
# Linux
curl -LO https://github.com/sgreben/subst/releases/download/1.1.1/subst_1.1.1_linux_x86_64.zip
unzip subst_1.1.1_linux_x86_64.zip
# OS X
curl -LO https://github.com/sgreben/subst/releases/download/1.1.1/subst_1.1.1_osx_x86_64.zip
unzip subst_1.1.1_osx_x86_64.zip
# Windows
curl -LO https://github.com/sgreben/subst/releases/download/1.1.1/subst_1.1.1_windows_x86_64.zip
unzip subst_1.1.1_windows_x86_64.zip
```
## Use it
`subst` uses key=value mappings given as CLI arguments, reads from stdin, and writes to stdout. The stdin input is line-buffered.
```text
subst [OPTIONS] [KEY=VAL [KEY=VAL...]]
Usage of subst:
-q suppress all logs
-escape string
set the escape string. if set, a '$' preceded by the escape string does not lead to expansion
-unknown value
handling of unknown keys, one of [ignore empty error] (default ignore)
```
### Examples
```shell
$ cat template.yaml
name: $NAME
url: $URL
comment: $COMMENT
$ cat template.yaml | subst -q NAME=jp URL=github.com/sgreben/jp COMMENT=
name: jp
url: github.com/sgreben/jp
comment:
$ cat template.yaml | subst -q NAME=jp
name: jp
url: $URL
comment: $COMMENT
$ cat template.yaml | subst -q -unknown=empty NAME=jp
name: jp
url:
comment:
```
Without the `-q` flag, `subst` also prints to stderr:
```shell
2018/04/16 15:18:37 undefined key: $URL, using value "$URL"
2018/04/16 15:18:37 undefined key: $COMMENT, using value "$COMMENT"
```
You can substitute environment variables (like `envsubst`) by letting the shell substitute their values:
```shell
$ subst USER="$USER" SHELL="$SHELL"
$USER
sgreben
$SHELL
/bin/zsh
```
To ignore occurrences of defined variables, you can define an escape string using the `-escape` flag:
```shell
$ echo 'unescaped: $X, ${X}. escaped: \$X, \${X}.' | subst -escape '\' X=value
unescaped: value, value. escaped: $X, ${X}.
```
## Comments
Feel free to [leave a comment](https://github.com/sgreben/subst/issues/1) or create an issue.