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You Should Learn Regex

blog.patricktriest.com

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Re: You Should Learn Regex

#41

Post by kqr »

philipov wrote: post #35
submeta wrote: post #11

When I used to code in Perl (more than ten years ago) I tended to solve many many things using regexes. I tried to reduce many programming challenges into transformations that I could do via regexes. Why? Because regular expressions are first class citizens in Perl. And Perl made me learn and use them. (Reminds me of a an APL programmer that saw vectors everywhere.) When I replaced Perl with Python in my toolbox I ab…

Regex patterns might not be first class citizens in python, but they're easy enough to use, and I think they're ultimately more powerful than in Perl. I don't remember being able to use a callback to calculate my replace string as a function of the match results when doing substitution in Perl. It's super easy to do tokenization with python regexes. We lose first class patterns, but gain first class functions and cla…

Not to mention that writing a composable first-class API to contruct regexes should be fairly elementary in Python.

Re: You Should Learn Regex

#42

Post by yorwba »

papey wrote: post #24

Why the fuck on earth, people cat and pip stuff to grep ? grep cat take files from args !

I cat files into programs that can take their inputs both from stdin and a given file, although I know people call that "useless". I do it because it makes my pipelines more uniform, by keeping the direction of data flow from left to right. It also makes it easier to insert additional processing steps, or changing the input from a file to the output of a program. Maybe I'm a fool for writing Bash like Forth, but I prefer it that way.

Re: You Should Learn Regex

#43

Post by [deleted] »

kqr wrote: post #31
Invisig0th wrote: post #25

Earlier quoted context omitted.

The article you link to addresses just the one use case where you are registering a new user. Email addresses in business applications are just as often NOT the address of your user. Sales contacts, managers, points of contact, customer support addresses, etc. -- none of these should ever be validated by sending an e-mail. So you still need to validate the hard way in plenty of scenarios.

...but unless you actually send an email it is still just as unvalidated as it was before. Regexes aren't a tool to determine that a string refers to a mailbox capable of receiving mail. If you use regexes (or any other method of that does not send emails) all you're saying is that you don't actually care whether or not the string points to a recipient (much less the correct recipient). And don't get me wrong. It is…

[deleted]

Re: You Should Learn Regex

#44

Post by asicsp »

yorwba wrote: post #42
papey wrote: post #24

Why the fuck on earth, people cat and pip stuff to grep ? grep cat take files from args !

I cat files into programs that can take their inputs both from stdin and a given file, although I know people call that "useless". I do it because it makes my pipelines more uniform, by keeping the direction of data flow from left to right. It also makes it easier to insert additional processing steps, or changing the input from a file to the output of a program. Maybe I'm a fool for writing Bash like Forth, but I pr…

you can still do `see https://en.wikipedia.org/wiki/Cat_(Unix)#UUOC_.28Useless_Use...

>Beyond other benefits, the input redirection forms allow command to perform random access on the file, whereas the cat examples do not. This is because the redirection form opens the file as the stdin file descriptor which command can fully access, while the cat form simply provides the data as a stream of bytes.

commands like `sort` are optimized to handle large input file

and how would you do `grep -l 'foo' *.txt` if you use `cat`?

or `awk 'NR==FNR{a[$1]; next} $1 in a' file1 file2`

or `grep -Fxf file1 file2` and so on....

Re: You Should Learn Regex

#45

Post by [deleted] »

kqr wrote: post #31
Invisig0th wrote: post #25

Earlier quoted context omitted.

The article you link to addresses just the one use case where you are registering a new user. Email addresses in business applications are just as often NOT the address of your user. Sales contacts, managers, points of contact, customer support addresses, etc. -- none of these should ever be validated by sending an e-mail. So you still need to validate the hard way in plenty of scenarios.

...but unless you actually send an email it is still just as unvalidated as it was before. Regexes aren't a tool to determine that a string refers to a mailbox capable of receiving mail. If you use regexes (or any other method of that does not send emails) all you're saying is that you don't actually care whether or not the string points to a recipient (much less the correct recipient). And don't get me wrong. It is…

[deleted]

Re: You Should Learn Regex

#46

Post by asicsp »

quotable_cow wrote: post #29
asicsp wrote: post #23

haven't read/processed the article fully, some nitpicks: * `\b([01]?[0-9]|2[0-3]):([0-5]\d)\b` you are using both [0-9] and \d, is that intentional? * `cat test.txt | grep -E "^[0-9]+$"` UUoC and double quotes subjected to shell interpretation, should be `grep -E '^[0-9]+$' test.txt` or `grep -xE '[0-9]+' test.txt` * `(?i)` won't work with `grep -E` (or at least not for me on GNU grep). features of BRE/ERE and PCRE l…

Thanks, that's all very useful feedback.

for the ls parsing example, you can do

shopt -s nocaseglob

ls ~/Downloads/*.{png,jpg,jpeg,gif,webp}

----

for command line tools (grep/sed/awk/sort/etc), you can refer my ongoing project (https://github.com/learnbyexample/Command-line-text-processi...) as resource :)

Re: You Should Learn Regex

#47

Post by Invisig0th »

kqr wrote: post #31
Invisig0th wrote: post #25

Earlier quoted context omitted.

The article you link to addresses just the one use case where you are registering a new user. Email addresses in business applications are just as often NOT the address of your user. Sales contacts, managers, points of contact, customer support addresses, etc. -- none of these should ever be validated by sending an e-mail. So you still need to validate the hard way in plenty of scenarios.

...but unless you actually send an email it is still just as unvalidated as it was before. Regexes aren't a tool to determine that a string refers to a mailbox capable of receiving mail. If you use regexes (or any other method of that does not send emails) all you're saying is that you don't actually care whether or not the string points to a recipient (much less the correct recipient). And don't get me wrong. It is…

Regex validation cannot verify that an email address is functioning any more than it can verify that a phone number is functioning. But if an address or a number passes formatting checks, one can indeed consider that data "validated". That's what that term means in the business software development industry. We're verifying if the data entered COULD be correct, not double-checking that it IS correct.

You are correct to say that those emails may still bounce, and the phone calls may also not go through. We completely understand that. For this reason, in very specific situations (like registering a new user), we do take that extra step to make sure the communication channel actually works. But there are plenty of situations where that makes absolutely no sense, and/or adds very little value for the cost. Knowing the difference between these two very different use cases certainly does not indicate that these people "don't actually care" about the accuracy of their data.

Re: You Should Learn Regex

#48

Post by spoxaka »

quotable_cow wrote: post #29
asicsp wrote: post #23

haven't read/processed the article fully, some nitpicks: * `\b([01]?[0-9]|2[0-3]):([0-5]\d)\b` you are using both [0-9] and \d, is that intentional? * `cat test.txt | grep -E "^[0-9]+$"` UUoC and double quotes subjected to shell interpretation, should be `grep -E '^[0-9]+$' test.txt` or `grep -xE '[0-9]+' test.txt` * `(?i)` won't work with `grep -E` (or at least not for me on GNU grep). features of BRE/ERE and PCRE l…

Thanks, that's all very useful feedback.

I just have to ask. Doesn't the above comment kind of defeats the article premise?

Re: You Should Learn Regex

#49

Post by philipov »

kqr wrote: post #41
philipov wrote: post #35

Earlier quoted context omitted.

Regex patterns might not be first class citizens in python, but they're easy enough to use, and I think they're ultimately more powerful than in Perl. I don't remember being able to use a callback to calculate my replace string as a function of the match results when doing substitution in Perl. It's super easy to do tokenization with python regexes. We lose first class patterns, but gain first class functions and cla…

Not to mention that writing a composable first-class API to contruct regexes should be fairly elementary in Python.

oh what a good idea... wait, surely someone's already built this, right? like sqlalchemy's expression language, but for regex. If noone's built that yet, I'd build that.

Re: You Should Learn Regex

#50

Post by davidkuhta »

lowmagnet wrote: post #3

> From validating email addresses Guys, no. Send an email. https://davidcel.is/posts/stop-validating-email-addresses-wi...

In fairness, the author does make note of that:

Note - In a real-world application, validating an email address using a regular expression is not enough for many situations, such as when a user signs up. Once you have confirmed that the input text is an email address, you should always follow through with the standard practice of sending a confirmation/activation email.

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