preg_replace with backreference AND curly braces 1

[OsakaWebbie]

Trying to use PHP to construct TeX code, and TeX loves curly braces. But in PHP, curly braces are interpreted as part of parsing variables. I have strings like "Dm7 G" (yes, they are guitar chords), and want them to become like "Dm\Sup{7} G".

If I do this:

preg_replace("/([0-9]+)/","\\Sup{$1}",$chord)

I get a syntax error.

But if I do this:

preg_replace("/([0-9]+)/","\\Sup\{$1\}",$chord)

the backslashes actually end up in the resulting string, which is not desired.

Suggestions?

 

[feherke]

Hi

But in PHP, curly braces are interpreted as part of parsing variables.

Correct. So you have to stop the variable parsing :

[COLOR=darkgoldenrod]preg_replace[/color][teal]([/teal][green][i]"/([0-9]+)/"[/i][/green][teal],[/teal][green][i]"\\Sup{[highlight]\[/highlight]$1}"[/i][/green][teal],[/teal][navy]$chord[/navy][teal]);[/teal]

May be caused by my affinity for shell scripting, but I generally prefer to use the most restrictive quoting possible in each case. In this case I would use single quotes ( ' ) :

[COLOR=darkgoldenrod]preg_replace[/color][teal]([/teal][green][i]'/([0-9]+)/'[/i][/green][teal],[/teal][green][i][highlight #fcc]'[/highlight]\\Sup{$1}[highlight #fcc]'[/highlight][/i][/green][teal],[/teal][navy]$chord[/navy][teal]);[/teal]

Feherke.
[link feherke.github.com/]

http://feherke.github.com/

[/url]

 

[OsakaWebbie]

Thanks! I must be losing my mind - I thought I tried that second version (among various things I tried in desperation) and got an error. Anyway, naturally you know what you're doing, and both solutions work.

So you have to stop the variable parsing...

I'm a little confused - when I stop the parsing (either by escaping the $ or using single quotes), why don't I end up with a literal "Dm\Sup{$1} G"?

 

[feherke]

Hi

when I stop the parsing [gray](...)[/gray] why don't I end up with a literal "Dm\Sup{$1} G"?

In this case $1 is not a variable, it is a placeholder. The [tt]preg_replace()[/tt] function replaces such placeholders after her finds a substring matching the regular expression and extracted the captured groups.

Variable parsing had to be stopped to avoid the PHP interpreter trying to interpret $1 as variable before the [tt]preg_replace()[/tt] function receives its string parameters.

Feherke.
[link feherke.github.com/]

http://feherke.github.com/

[/url]

 

[OsakaWebbie]

Okay, thanks for the clarification.