3 ms·

I hate to be "that guy" but someone has to say something about the Useless Use of Cat. http://www.catb.org/jargon/html/U/UUOC.html http://www.catb.org/jargon/h

I hate to be "that guy" but someone has to say something about the Useless Use of Cat. http://www.catb.org/jargon/html/U/UUOC.html http://www.catb.org/jargon/html/U/UUOC.html

davidu 12y ago
I believe in this case, based on the author clearly having some mastery of the art, it was used to extend the example for the sake of explanation. There are lots of ways to tighten up the example, if needed.
djur 12y ago
I've never agreed with the UUOC concept when applied to pipelines. Using cat in a pipeline for a single file makes the flow clearly unidirectional, prevents certain types of errors like switching > and <, allows the command to be easily modified to handle multiple files or a glob, and frankly just seems easier to read. Considering the tiny overhead of an additional cat process, UUOC these days feels like nitpicking.
- unhammer 12y ago
  Also, the cat makes for faster testing. I tend to start out with e.g. head bigfile.1.txt | grep | awk | stuff and refine things, and when output looks right, it's a simple "Ctrl+A Meta+D cat RET" to run it on the full output. Or vice versa if I suddenly want to go back to testing part of bigfile (or exchange the cat for "grep something"). If I want to change that to "< bigfile.1.txt", I have to "Ctrl+A Meta+D < Meta+F Meta+F Meta+F Ctrl+D Ctrl+D" – the extra keypresses are to delete the first "|" symbol. And if I suddenly want to change it back to head or grep, I have to reinsert the | (also I often by habit do Meta+D instead of Ctrl+D at the beginning of the line, which doesn't work as intended if the first token is "<" instead of "cat"). Those useless cats are quite handy when doing a lot of shell work.
  - JetSpiegel 12y ago
    You can use <bigfile.txt head | grep | awk
    - unhammer 12y ago
      So if I want to change that to the whole file, I "just" have to Ctrl+A Meta+F Meta+F Meta+D Ctrl+D Ctrl+D RET. That's not really an improvement – especially since it depends on how many dots or similar are in the filename. Also, that's a Useless Use of head, since grep has the option "-m10"
      - JetSpiegel 12y ago
        grep -m "Stop reading a file after NUM matching lines", while head -10 takes the first 10 lines and searches on them. Different things.
        unhammer 12y ago
        doh! you're right, I wasn't thinking :-)
- rdc12 12y ago
  But then the article has this "(If we move grep to run immediately after cat, and before putting data into Redis, this operation runs more than 1,200 times faster.)" Which does indicate that in some cases the UUOC is justified (thou in this case the cat remains)

I hate to be "that guy" but someone has to say something about the Useless Use of Cat. http://www.catb.org/jargon/html/U/UUOC.html http://www.catb.org/jargon/html/U/UUOC.html

davidu 12y ago

I believe in this case, based on the author clearly having some mastery of the art, it was used to extend the example for the sake of explanation. There are lots of ways to tighten up the example, if needed.

djur 12y ago

I've never agreed with the UUOC concept when applied to pipelines. Using cat in a pipeline for a single file makes the flow clearly unidirectional, prevents certain types of errors like switching > and <, allows the command to be easily modified to handle multiple files or a glob, and frankly just seems easier to read. Considering the tiny overhead of an additional cat process, UUOC these days feels like nitpicking.

unhammer 12y ago
Also, the cat makes for faster testing. I tend to start out with e.g. head bigfile.1.txt | grep | awk | stuff and refine things, and when output looks right, it's a simple "Ctrl+A Meta+D cat RET" to run it on the full output. Or vice versa if I suddenly want to go back to testing part of bigfile (or exchange the cat for "grep something"). If I want to change that to "< bigfile.1.txt", I have to "Ctrl+A Meta+D < Meta+F Meta+F Meta+F Ctrl+D Ctrl+D" – the extra keypresses are to delete the first "|" symbol. And if I suddenly want to change it back to head or grep, I have to reinsert the | (also I often by habit do Meta+D instead of Ctrl+D at the beginning of the line, which doesn't work as intended if the first token is "<" instead of "cat"). Those useless cats are quite handy when doing a lot of shell work.
- JetSpiegel 12y ago
  You can use <bigfile.txt head | grep | awk
  - unhammer 12y ago
    So if I want to change that to the whole file, I "just" have to Ctrl+A Meta+F Meta+F Meta+D Ctrl+D Ctrl+D RET. That's not really an improvement – especially since it depends on how many dots or similar are in the filename. Also, that's a Useless Use of head, since grep has the option "-m10"
    - JetSpiegel 12y ago
      grep -m "Stop reading a file after NUM matching lines", while head -10 takes the first 10 lines and searches on them. Different things.
      - unhammer 12y ago
        doh! you're right, I wasn't thinking :-)
rdc12 12y ago
But then the article has this "(If we move grep to run immediately after cat, and before putting data into Redis, this operation runs more than 1,200 times faster.)" Which does indicate that in some cases the UUOC is justified (thou in this case the cat remains)