| marp | theme |
|---|---|
true |
nord |
Connor Sample - https://tabulate.tech
- Sequences of characters that define a search pattern
- Pattern matching and manipulation of text
- Searching for specific patterns in log files
- Parsing and extracting data from structured text
- Validating input in scripts and programs
- Utilies such as
grep,vim,sed, andawksupport regex
- Literal characters:
/hello/ - Anchors: Define positions within the text
/^start//end$/
- Or: Combine two predicates together with the OR operator
/start|end/
/[a-z]//[A-Z0-9?]//[^A-Z]/- The dot matches any character except line endings (
\n,\r)/c.t/
- Escape sequences can be used as shorthands
\s\d\t
- Quantifiers: Specify the number of occurrences
/[0-9]{3}//[0-9]{3,5}//[A-Za-z]*//[A-Za-z]+//[a-z]?/
-
Finding patterns in files:
- Use
grepto search for specific strings or patterns grep 'error' logfile.txtgrep -E '([0-9]{1,3}\.){3}[0-9]{1,3}' access.log
- Use
-
Replacing text in files:
- Use
sedorawkto perform find and replace operations sed -i 's/\.html"/"/g' file.txt
- Use
-
Validating input:
- Ensure input adheres to specific formats or constraints
<input type="text" pattern="[A-Za-z]{3}"
- Grouping and capturing: Use parentheses to capture parts of a match
- Text: "Name: John, Age: 50"
- Regex:
Name: (\w+), Age: (\d+) - Non-capturing groups can be created as such:
(?:\w+)
- Lookahead and lookbehind: Specify conditions ahead or behind the match
- Text: "apple, banana, pear"
- Regex:
\w+(?=,) - Text: "apple - banana - pear"
- Regex:
(?<=-) \w+
\bto match the position between word characters and non word characters- Zero-width assertion
- "this is test" vs "this is testing"
-
Backreferences: Refer to captured groups
- Text: "Ray loves Python so so much"
- Regex:
(\b\w+\b) \1
-
Greedy vs lazy matching: Control the greediness of quantifiers with
?- Text:
<div>Super</div> <p>Cool</p>
- Text:
Text: "I have 3 apples and 5 oranges."
Regex: \d+
\b can be used to match "word-boundaries", which is the space around word
characters (\w).
Text: "The quick brown fox jumps over the lazy dog."
Regex: \b\w{3}\b
Use capture groups to extract March, 5, and 2024.
Text: March 5th, 2024
Regex: ([A-Za-z]+)\s+(\d{1,2})(?:[A-Za-z]*),\s+(\d{4})
Text: "Contact us at [email protected]."
Simplified email specification:
- Any uppercase or lowercase letters; numbers; the following symbols:
._%+-
Domain specification:
- Any letter (case insensitive), numbers, or the hyphen.
- Also support subdomains and TLDs of various lengths
Use \b to ensure the email is standalone
Regex: \b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b
- Don't create an overconvoluted and undocumented mess
- Understand when you should and shouldn't use regex
(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:
[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\
[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)
+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|
[1-9]?[0-9]))\.){3}(?:(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9])|
[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\
[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])
import re
pattern = re.compile(r"""
\d+ # match one or more digits
\. # match the `.` character
[A-Za-z]{5} # match 5 letters of any case
""", re.X)
pattern2 = re.compile(r"""
(?x) # verbose mode
\d* # match an optional digit
""")- Extract the three parts of a phone number with capturing groups
- Parse dash-delimited dates (
2024-03-21) - Write a regex to match URLs
- Extract the parts of markdown links
[Display Text](https://tabulate.tech)
- Extract the arguments from a Python function signature:
def func(arg1, arg2):