Process Module

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This XQuery Module provides functions for executing system commands from XQuery.

Contents

Conventions

Updated with Version 9.0:

All functions and errors in this module are assigned to the http://basex.org/modules/proc namespace, which is statically bound to the proc prefix.

Functions

proc:system

Updated with Version 9.0: new input option; revised error handling.

Signatures proc:system($cmd as xs:string) as xs:string
proc:system($cmd as xs:string, $args as xs:string*) as xs:string
proc:system($cmd as xs:string, $args as xs:string*, $options as map(xs:string, xs:string)) as xs:string
Summary Executes the specified command in a separate process and returns the result as string. $cmd is the name of the command, arguments to the command may be specified via $args. The $options parameter contains process options:
  • encoding: convert result to the specified encoding. If no encoding is supplied, the system’s default encoding is used.
  • timeout: abort process execution after the specified number of seconds.
  • dir: process command in the specified directory.
  • input: standard string input (stdin) to be passed on to the command.
Errors encoding: the specified encoding does not exist or is not supported.
timeout: the specified timeout was exceeded.
error: the command could not be executed, or an I/O exception was raised.
code....: If the commands returns an exit code different to 0, an error will be raised. Its code will consist of the letters code and four digits with the exit code.
Examples
  • proc:system('date') returns the current date on a Linux system.
  • Analyses the given input and counts the number of lines, words and characters (provided that wc is available on the system):
proc:system(
  'wc', (),
  map { 'input': 'A B' || out:nl() || 'C' }
)
  • The following example returns “Command not found” (unless xyz is a valid command on the system):
try {
  proc:system('xyz')
} catch proc:error {
  'Command not found: ' || $err:description
}

proc:execute

Signatures proc:execute($cmd as xs:string) as element(result)
proc:execute($cmd as xs:string, $args as xs:string*) as element(result)
proc:execute($cmd as xs:string, $args as xs:string*, $options as map(xs:string, xs:string)) as element(result)
Summary Executes the specified command in a separate process and returns the result as element:
  • $cmd is the name of the command, and arguments to the command may be specified via $args.
  • The same $options are allowed as for proc:system.
  • Instead of the proc:error error, the error message and process code will be assigned to the returned elements.
  • Instead of the proc:code.... error, the error message will be assigned to the returned element (no process code will be returned).

The result has the following structure:

<result>
  <output>...output...</output>
  <error>...error message...</error>
  <code>...process code...</code>
</result>
Errors encoding: the specified encoding does not exist or is not supported.
timeout: the specified timeout was exceeded.
Examples
  • proc:execute('dir', '\') returns the files of the root directory of a Windows system.
  • proc:execute('ls', ('-l', '-a')) executes the ls -la command on Unix systems.

proc:fork

Introduced with Version 9.0:

Signatures proc:fork($cmd as xs:string) as element(result)
proc:fork($cmd as xs:string, $args as xs:string*) as element(result)
proc:fork($cmd as xs:string, $args as xs:string*, $options as map(xs:string, xs:string)) as element(result)
Summary Executes the specified command and ignores the result. $cmd is the name of the command, and arguments to the command may be specified via $args. The same $options are allowed as for proc:system (but the encoding will be ignored).
Errors encoding: the specified encoding does not exist or is not supported.
Examples
  • proc:fork('sleep', '5'): sleep for 5 seconds (no one should notice).

proc:property

Signatures proc:property($name as xs:string) as xs:string?
Summary Returns the system property, specified by $name, or a context parameter of the web.xml file with that name (see Web Applications). An empty sequence is returned if the property does not exist. For environment variables of the operating system, please use fn:environment-variable.
Examples
  • map:merge(proc:property-names() ! map:entry(., proc:property(.))) returns a map with all system properties.

proc:property-names

Signatures proc:property-names() as xs:string*
Summary Returns the names of all Java system properties and context parameters of the web.xml file (see Web Applications). For environment variables of the operating system, please use fn:available-environment-variables.
Examples
  • proc:property('java.runtime.version') returns the version of the Java runtime engine.

Errors

Updated with Version 9.0:

Code Description
code... The result of a command call with an exit code different to 0.
code9999 A command could not be executed.
encoding The specified encoding does not exist or is not supported.
timeout The specified timeout was exceeded.

Changelog

Version 9.0
Version 8.6
Version 8.3

The module was introduced with Version 7.3.

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