Eval Operations#

This page documents all eval operations.

!eval#

Evaluate environment variables in a document

The !eval operation expands the expressions in the strings beneath it. Each is an expr-lang expression evaluated against the evaluation environment (o eval -e name=value). $[expr] is replaced by the expression's value as text; a string that is exactly .[expr] is replaced by the value itself, keeping its type. $USER is not an expression and stays as it is written; .[getenv("USER")] reads the OS environment.

Child: Document whose strings hold $[...] or .[...] expressions

Examples:

1. ```tony name: !eval '.[getenv("USER")]'

   2. ```tony
   path: !eval "/home/$[user]/config"
   

See also: !osenv, !file

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!exec#

Execute a shell command and capture output

The !exec operation executes a shell command and captures its stdout. The child must be a string containing the command to execute. The command is run with 'sh -c'.

Child: String containing shell command

Examples:

1. ```tony date: !exec "date -u +%Y-%m-%d"

   2. ```tony
   hostname: !exec "hostname"
   

See also: !file, !script

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!file#

Load content from a file or URL

The !file operation loads content from a local file path or HTTP/HTTPS URL. The child must be a string containing the path or URL. The content is answered as a string, not parsed; !tovalue.file parses it.

Child: String containing file path or URL

Examples:

1. ```tony motd: !file "/etc/motd"

   2. ```tony
   data: !tovalue.file "https://example.com/data.tony"
   

See also: !exec, !eval

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!osenv#

Get value from OS environment variable

The !osenv operation retrieves the value of an OS environment variable. The child must be a string containing the environment variable name.

Child: String containing environment variable name

Examples:

1. ```tony home: !osenv "HOME"

   2. ```tony
   path: !osenv "PATH"
   

See also: !eval

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!toint#

Convert a value to an integer

The !toint operation converts its child value to an integer. A number converts when it is a whole number an int64 holds (3.0 is 3; 3.5 is refused), true and false are 1 and 0, and a string must hold a base-10 integer.

Child: Number, bool, or string value to convert

Examples:

1. ```tony version: !toint "123"

   **See also:** [`!tostring`](./eval.md#tostring), [`!tovalue`](./eval.md#tovalue)
   
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   ## `!tostring`
   
   **Convert a value to a string**
   
   The !tostring operation converts its child value to a string representation.
   
   **Child:** Value to convert
   
   **Examples:**
   
   1. ```tony
   version_str: !tostring 123
   

See also: !toint, !tovalue

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