Regular Expressions: Difference between revisions
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Regex is short for Regular Expression and is a syntax that allows for powerful pattern matching. | Regex is short for Regular Expression and is a syntax that allows for powerful pattern matching. | ||
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== Multiline Edits == | == Multiline Edits == | ||
Most graphical text editors or word processors have a single line input for the Search/Replace dialog. This is unsuitable for many text edit situations where the string you're looking to replace spans multiple lines. | Most graphical text editors or word processors have a single line input for the Search/Replace dialog. This is unsuitable for many text edit situations where the string you're looking to replace spans multiple lines. When using [[VSCode]], although the search and replace dialog is single line, it will dynamically expand to multiple lines if you COPY/PASTE multiple lines into the 'find' portion. You can also use the 'regex' option and line-terminator escapes in your pattern (e.g. "this \n will \n search across \n multiple lines"). | ||
== Single Line == | == Single Line == | ||
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PHP has rich regular expression support. Perl obviously does too. So when you're at the command line with BASH, what's the best way to quickly search some content for a pattern using a rich regular expression? It can be hard to use bash because of all the quoting and interpolation. But, let's look at a couple examples of searching a PHP configuration file for variable assignments. | PHP has rich regular expression support. Perl obviously does too. So when you're at the command line with BASH, what's the best way to quickly search some content for a pattern using a rich regular expression? It can be hard to use bash because of all the quoting and interpolation. But, let's look at a couple examples of searching a PHP configuration file for variable assignments. | ||
Using perl, it's easy to print out only the parenthetical sub-expression | Using perl, it's easy to print out only the parenthetical sub-expression | ||
< | <syntaxhighlight lang="bash"> | ||
perl -ne 'print $1 if /\$wgDBuser.*"(.*)"/' ./LocalSettings.php | perl -ne 'print $1 if /\$wgDBuser.*"(.*)"/' ./LocalSettings.php | ||
</ | </syntaxhighlight> | ||
Using grep, you have \K for variable length look-behind but it may not be available on older systems. Thus, you may need to use cut | Using grep, you have \K for variable length look-behind but it may not be available on older systems. Thus, you may need to use cut | ||
< | <syntaxhighlight lang="bash"> | ||
grep -Po '(?<=\$wgDBuser).*"(.*)"' ./LocalSettings.php | cut -d \" -f 2 | grep -Po '(?<=\$wgDBuser).*"(.*)"' ./LocalSettings.php | cut -d \" -f 2 | ||
</ | </syntaxhighlight> | ||
== Resources == | == Resources == | ||