4 ms·

I love the comment that someone dropped on the post. One could replace the first Ruby script by a one-liner: "cat /tmp/com.txt | awk '{ print substr($1, 1, leng

I love the comment that someone dropped on the post. One could replace the first Ruby script by a one-liner: "cat /tmp/com.txt | awk '{ print substr($1, 1, length($1) -5) }' | uniq > domains.txt"

deleted 4y ago
[deleted]
Grimburger 4y ago
Classic useless use of cat?
- jacquesm 4y ago
  I don't agree with the whole 'useless use of cat' meme: cat creates an output stream, which in turn allows you to build up the subsequent command bit by bit and allows you to cut and past chunks from useful building blocks you keep in a file. The first command changes all the time so by using 'cat' those blocks remain reusable, everything will use the piped input that cat sends if there is no preceding program, rather than to have to insert < somefile in the middle of the first command.
  - Grimburger 4y ago
    I'd agree with avoiding the < somefile redirection because it's sorta annoying to grok in one-liners. But in this case the file would just go after the awk command.
  - hddqsb 4y ago
    It's possible to avoid `cat` and still keep the filename separate from the rest of the command by placing the redirection at the start of the command: < /tmp/com.txt awk ... It might look a little odd, but it's portable.
    - monsieurbanana 4y ago
      I don't know about you, but I usually like seeing what's in the file before I spend time writing a awk command on it. cat myfile.txt # check the file because I'm not even sure that's the correct name cat myfile.txt | awk blablabla # no I didn't forget awk syntax, I swear I would be afraid of any person that after this, goes back and rewrites the beginning of the line to replace cat with a redirection. Even with "ctrl-a alt-d < alt-f alt-f ctrl-d ctrl-d ctrl-e" that replaces cat with < and removes the pipe, which any emacs user can pull off in it's sleep
      - prmoustache 4y ago
        I usually use head or less for that. Using cat for first look is usually looking for trouble if the file is huge or some binary file.
      - Beltalowda 4y ago
        If you use zsh then just "<myfile.txt" should work too, which opens the file in $PAGER. Doesn't seem to work in bash though, with the default config anyway, but maybe it can be configured. I don't care if people use "cat" or "<" and the whole "useless use of cat" is stupid >99% of the time, but I've gotten in to the habit of using <file as it's shorter to type ("<file cmd" vs. "cat file | cmd").
  - cannam 4y ago
    Totally with you there. "Useless use of cat" is usually good practice, not bad. It's clearer - the structure indicates right at the front what it is going to do, namely read a file and pass it through a pipeline. There is no need to read ahead to find out what the source material is. It's safer - "cat" is a read-only operation, once you've written that command up-front there is no longer a risk of overwriting the original file with a typo in the rest of the pipeline. It's simpler to construct and nicely orthogonal to the rest of the pipeline - you can write the "cat" and then season the rest to taste (as you suggested). I will occasionally remove cat from a very heavily-used loop, but as a default style it's fine.
    - pmoriarty 4y ago
      "It's safer - "cat" is a read-only operation, once you've written that command up-front there is no longer a risk of overwriting the original file with a typo in the rest of the pipeline." With zsh you can prevent such accidents by "setopt NO_CLOBBER" The result is that if you "foo > bar" and "bar" exists, zsh will refuse to overwrite "bar" and give you an error: "zsh: file exists: bar" This makes constructs such "foo < bar > baz" perfectly safe, because accidentally typing "foo > bar > baz" will error out when "bar" (or "baz") already exists. (PS: if you want to force zsh to overwrite the file even when NO_CLOBBER is set you can "foo >| bar")
      - lelanthran 4y ago
        That doesn't help with sed -i and similar things. Zsh stops redirection errors, it won't help even if cat is in the front.
        pmoriarty 4y ago
        "That doesn't help with sed -i and similar things." Can you give an example? I don't know what you mean. "Zsh stops redirection errors" Which is what the post I was answering to was complaining about, wasn't it? "it won't help even if cat is in the front" Why not? "cat > foo" will error out if "foo" exists and NO_CLOBBER is set.
  - Grimburger 4y ago
    In this particular case why is cat /tmp/com.txt | awk '{ print substr($1, 1, length($1) -5) }' | uniq > domains.txt preferable to: awk '{ print substr($1, 1, length($1) -5) }' /tmp/com.txt | uniq > domains.txt
  - kevincox 4y ago
    You can do <somefile awk ... | ... The redirect doesn't have to appear "out of order" at the end of the command. In zsh you can even do just `<somefile` to print it (equivalent to `cat somefile`, very useful for reading files into variables) although in bash that appears to do nothing.
- itronitron 4y ago
  my initial reading was that they were adding 'cat' as a prefix to everything...
- SnowHill9902 4y ago
  You don’t always need the shortest pipe.
dt3ft 4y ago
This does not use a dictionary, spitting out everything rather than words which exist in said dictionary.
kouteiheika 4y ago
One could replace the first Ruby script by a Ruby one-liner too: ruby -e "puts File.read('/tmp/com.txt').scan(/^[^.]+/).uniq" Personally I almost never use any of the standard Unix tools like `awk` etc. since an equivalent Ruby script is almost always shorter and easier to write. (There are exceptions of course; and in really simple cases the standard tools will obviously still win.) I think it's a shame that Ruby never really got popular as a general purpose scripting language, since it has that nice property that it's often as short as Perl while still being readable.

I love the comment that someone dropped on the post. One could replace the first Ruby script by a one-liner: "cat /tmp/com.txt | awk '{ print substr($1, 1, length($1) -5) }' | uniq > domains.txt"

deleted 4y ago

[deleted]

Grimburger 4y ago

Classic useless use of cat?

jacquesm 4y ago
I don't agree with the whole 'useless use of cat' meme: cat creates an output stream, which in turn allows you to build up the subsequent command bit by bit and allows you to cut and past chunks from useful building blocks you keep in a file. The first command changes all the time so by using 'cat' those blocks remain reusable, everything will use the piped input that cat sends if there is no preceding program, rather than to have to insert < somefile in the middle of the first command.
- Grimburger 4y ago
  I'd agree with avoiding the < somefile redirection because it's sorta annoying to grok in one-liners. But in this case the file would just go after the awk command.
- hddqsb 4y ago
  It's possible to avoid `cat` and still keep the filename separate from the rest of the command by placing the redirection at the start of the command: < /tmp/com.txt awk ... It might look a little odd, but it's portable.
  - monsieurbanana 4y ago
    I don't know about you, but I usually like seeing what's in the file before I spend time writing a awk command on it. cat myfile.txt # check the file because I'm not even sure that's the correct name cat myfile.txt | awk blablabla # no I didn't forget awk syntax, I swear I would be afraid of any person that after this, goes back and rewrites the beginning of the line to replace cat with a redirection. Even with "ctrl-a alt-d < alt-f alt-f ctrl-d ctrl-d ctrl-e" that replaces cat with < and removes the pipe, which any emacs user can pull off in it's sleep
    - prmoustache 4y ago
      I usually use head or less for that. Using cat for first look is usually looking for trouble if the file is huge or some binary file.
    - Beltalowda 4y ago
      If you use zsh then just "<myfile.txt" should work too, which opens the file in $PAGER. Doesn't seem to work in bash though, with the default config anyway, but maybe it can be configured. I don't care if people use "cat" or "<" and the whole "useless use of cat" is stupid >99% of the time, but I've gotten in to the habit of using <file as it's shorter to type ("<file cmd" vs. "cat file | cmd").
- cannam 4y ago
  Totally with you there. "Useless use of cat" is usually good practice, not bad. It's clearer - the structure indicates right at the front what it is going to do, namely read a file and pass it through a pipeline. There is no need to read ahead to find out what the source material is. It's safer - "cat" is a read-only operation, once you've written that command up-front there is no longer a risk of overwriting the original file with a typo in the rest of the pipeline. It's simpler to construct and nicely orthogonal to the rest of the pipeline - you can write the "cat" and then season the rest to taste (as you suggested). I will occasionally remove cat from a very heavily-used loop, but as a default style it's fine.
  - pmoriarty 4y ago
    "It's safer - "cat" is a read-only operation, once you've written that command up-front there is no longer a risk of overwriting the original file with a typo in the rest of the pipeline." With zsh you can prevent such accidents by "setopt NO_CLOBBER" The result is that if you "foo > bar" and "bar" exists, zsh will refuse to overwrite "bar" and give you an error: "zsh: file exists: bar" This makes constructs such "foo < bar > baz" perfectly safe, because accidentally typing "foo > bar > baz" will error out when "bar" (or "baz") already exists. (PS: if you want to force zsh to overwrite the file even when NO_CLOBBER is set you can "foo >| bar")
    - lelanthran 4y ago
      That doesn't help with sed -i and similar things. Zsh stops redirection errors, it won't help even if cat is in the front.
      - pmoriarty 4y ago
        "That doesn't help with sed -i and similar things." Can you give an example? I don't know what you mean. "Zsh stops redirection errors" Which is what the post I was answering to was complaining about, wasn't it? "it won't help even if cat is in the front" Why not? "cat > foo" will error out if "foo" exists and NO_CLOBBER is set.
- Grimburger 4y ago
  In this particular case why is cat /tmp/com.txt | awk '{ print substr($1, 1, length($1) -5) }' | uniq > domains.txt preferable to: awk '{ print substr($1, 1, length($1) -5) }' /tmp/com.txt | uniq > domains.txt
- kevincox 4y ago
  You can do <somefile awk ... | ... The redirect doesn't have to appear "out of order" at the end of the command. In zsh you can even do just `<somefile` to print it (equivalent to `cat somefile`, very useful for reading files into variables) although in bash that appears to do nothing.
itronitron 4y ago
my initial reading was that they were adding 'cat' as a prefix to everything...
SnowHill9902 4y ago
You don’t always need the shortest pipe.

dt3ft 4y ago

This does not use a dictionary, spitting out everything rather than words which exist in said dictionary.

kouteiheika 4y ago

One could replace the first Ruby script by a Ruby one-liner too: ruby -e "puts File.read('/tmp/com.txt').scan(/^[^.]+/).uniq" Personally I almost never use any of the standard Unix tools like `awk` etc. since an equivalent Ruby script is almost always shorter and easier to write. (There are exceptions of course; and in really simple cases the standard tools will obviously still win.) I think it's a shame that Ruby never really got popular as a general purpose scripting language, since it has that nice property that it's often as short as Perl while still being readable.