From e8e03e7eda2c6d5fc9e0e5ea13bd46beb4417798 Mon Sep 17 00:00:00 2001
From: Thomas Voss <mail@thomasvoss.com>
Date: Sat, 9 Dec 2023 20:14:08 +0100
Subject: Genesis commit

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+# Grab — A better grep
+
+Grab is a more powerful version of the well-known Grep utility, making
+use of structural regular expressions as described by Rob Pike in [this
+paper][1].  Grab allows you to be far more precise with your searching
+than Grep, as it doesn’t constrain itself to working only on individual
+lines.
+
+Grab invokations must include a pattern string which specifies which text
+to match.  A pattern string consists of one or more commands.  A command
+is an operator followed by a delimiter, a regular expression (regex), and
+then terminated by the same delimiter.  The last delimiter of the last
+command is optional.
+
+For example, a pattern string may look like ‘`x/[a-z]+/ g.foo. v/bar/`’.
+
+The available operators are ‘g’, ‘v’, and ‘x’.  The ‘x' operator iterates
+over all matches of the corresponding regex.  This means that to print
+all numbers in a file, you can use the pattern string ‘`x/[0-9]+/`’.  The
+‘g’ and ‘v’ operators are filters.  The ‘g’ operator discards all results
+that don’t match the given regex, while the ‘v’ operator discards all
+results that *do* match the given regex.  This means that to select all
+numbers in a file that contain a ‘3’ but are not ‘1337’, you can use the
+pattern string ‘`x/[0-9]+/ g/3/ v/^1337$/`’.
+
+
+## Examples
+
+Get a list of your CPU flags.
+
+```sh
+# With Grep
+grep '^flags' /proc/cpuinfo \
+| sed 's/flags:\t*: //; y/ /\n/' \
+| sort \
+| uniq
+
+# With Grab
+grab 'x/^flags.*/ x/\w+/ v/flags/' /proc/cpuinfo \
+| sort \
+| uniq
+```
+
+1) Select lines that start with ‘flags’: `x/^flags.*/`
+2) Select all the words: `x/\w+/`
+3) Filter out the word ‘flags’: `v/flags/`
+
+
+## Additional Options
+
+The Grab utility has a few options that may be helpful for your usecase.
+For more detailed documentation, see the Grab manual with `man grab`.
+
+
+[1]: https://doc.cat-v.org/bell_labs/structural_regexps/se.pdf
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