diff options
author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-28 09:49:46 +0000 |
---|---|---|
committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-28 09:49:46 +0000 |
commit | 50b37d4a27d3295a29afca2286f1a5a086142cec (patch) | |
tree | 9212f763934ee090ef72d823f559f52ce387f268 /doc/antora/modules/unlang/pages/type/string/backticks.adoc | |
parent | Initial commit. (diff) | |
download | freeradius-upstream.tar.xz freeradius-upstream.zip |
Adding upstream version 3.2.1+dfsg.upstream/3.2.1+dfsgupstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | doc/antora/modules/unlang/pages/type/string/backticks.adoc | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/doc/antora/modules/unlang/pages/type/string/backticks.adoc b/doc/antora/modules/unlang/pages/type/string/backticks.adoc new file mode 100644 index 0000000..9372b4c --- /dev/null +++ b/doc/antora/modules/unlang/pages/type/string/backticks.adoc @@ -0,0 +1,38 @@ += Backtick-quoted string + +.Syntax +`{backtick}string{backtick}` + +The backtick operator is used to perform a run-time expansion +similar to what is done with the Unix shell. The contents of the string +are split into one or more sub-strings, based on intermediate +whitespace. Each substring is then expanded as described above for +double quoted strings. The resulting set of strings is used to execute a +program with the associated arguments. + +The output of the program is recorded, and the resulting data is +used in place of the input string value. Where the output is composed of +multiple lines, any carriage returns and line feeds are replaced by +spaces. + +For safety reasons, the full path to the executed program should be +given. In addition, the string is split into arguments _before_ the +substrings are dynamically expanded. This step is done both to allow +the substrings to contain spaces, and to prevent spaces in the +expanded substrings from affecting the number of command-line +arguments. + +For performance reasons, we recommend that the use of back-quoted +strings be kept to a minimum. Executing external programs is +relatively expensive, and executing a large number of programs for +every request can quickly use all of the CPU time in a server. If many +programs need to be executed, it is suggested that alternative ways to +achieve the same result be found. In some cases, using a real +programming language such as `lua`, `perl` or `python` may be better. + +.Examples + +`{backtick}/bin/echo hello{backtick}` + +// Copyright (C) 2020 Network RADIUS SAS. Licenced under CC-by-NC 4.0. +// Development of this documentation was sponsored by Network RADIUS SAS. |