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DOC: configuration: explain the rules regarding spaces in arguments

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Spaces around commas or parenthesis in expressions are generally part
of the value due to the long history of supporting unquoted arguments.
But this tends to come as a surprise to new users and sometimes creates
subtly invalid configurations. Let's add some text covering this.

This can be backported to 2.4.
This commit is contained in:
Willy Tarreau 2024-11-20 08:42:02 +01:00
parent 12fcd65468
commit 962d5e038f
1 changed files with 20 additions and 0 deletions
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doc/configuration.txt
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@ -852,6 +852,26 @@ double quotes inside (so that the double quotes are not stripped again):
arg2 ___________/ /
arg3 _______________/
But in this case it's important to note that delimiters embedded into the
higher level string remain pure characters and are not delimiters anymore. It
particularly means that spaces and tabs around commas are part of the string.
The example below is wrong on multiple points:
http-request set-path '%[path, regsub("(foo|bar)", blah, g)]'
------------ -------- --------------------------------------
word1 word2 word3=%[path, regsub("(foo|bar)", blah, g)]
|--------|---------||-----|--|
converter=" regsub" _/ / / /
arg1=(foo|bar) _/ / /
arg2=" blah" ___________/ /
arg3=" g" ______________/
The single fact of surrounding commas with spaces resulted in the spaces being
part of the field itself, hence the converter " regsub" (starting with a
space), which won't be found and will trigger an error, but more subtly, the
replacement string " blah" will insert a space in the output. A good rule of
thumb is to never insert unneeded spaces inside expressions.
When using regular expressions, it can happen that the dollar ('$') character
appears in the expression or that a backslash ('\') is used in the replacement
string. In this case these ones will also be processed inside the double quotes