Ask HN: How can I get better at bash?

Post by ikeyany » Mon, Jun 26, 2017, 8:26 PM UTC

Sean1708 wrote: post #66

ikeyany wrote: post #55

Earlier quoted context omitted.

> Like iterating over the files in a directory, for example. If you think that's easy in Bash you have either have a funny definition of easy Maybe I'm overlooking something...but why wouldn't this work: for file in $(ls); do { }; done

$ mkdir "hi there" $ mkdir "how are you" $ ls -l total 8 drwxr-xr-x 2 xxxxxxxx xxxx 4096 Jun 26 14:54 hi there drwxr-xr-x 2 xxxxxxxx xxxx 4096 Jun 26 14:54 how are you $ for f in $(ls); do echo $f; done hi there how are you

Post by mikerybka » Mon, Jun 26, 2017, 8:50 PM UTC

ASipos wrote: post #155

racl101 wrote: post #146

Earlier quoted context omitted.

What is a good learning resource for what the basic Unix process model (i.e. what you are describing?) Do you recommend a book or something like that? And preferably for a beginner?

Stevens - Advanced Programming in the Unix Environment Love - Linux System Programming The Unix-Haters Handbook (Unfortunately, the best resource ever for this kind of stuff, from which I learned, does not have an English translation.)

Post by syngrog66 » Mon, Jun 26, 2017, 9:12 PM UTC

Post by koala_man » Mon, Jun 26, 2017, 9:41 PM UTC

woodrowbarlow wrote: post #161

koala_man wrote: post #122

If you're not already familiar with it, I would suggest learning about the basic Unix process model -- fork, execve, wait, open, pipe, dup2 and friends. Bash is essentially a DSL for these. A lot of the weirdness you see in the language is due to these abstractions leaking through. For example: * Quoting is building execve's argv parameter. It's hard to quote correctly if you don't know what exactly you're working to…

> Quoting is building execve's argv parameter. can you expand on this? does this elucidate, e.g., variable substitution and the difference between single- and double-quotes? or does it just help demonstrate when you need quotes for an argument that may contain whitespace?

  execlp("cat", "$var", NULL);            // cat '$var'
  execlp("cat", "My", "File.txt", NULL);  // cat $var
  execlp("cat My File.txt", NULL);        // cmd="cat $var"; "$cmd"
  execlp("cat", "'My", "File.txt'", NULL);// cmd="cat '$var'"; $cmd
  execlp("cat", "My\\", "File.txt", NULL);// cmd="cat My\ File.txt"; $cmd
  execlp("cat", "'My File.txt'", NULL);   // var="'$var'"; cat "$var"
  execlp("cat", "\"$var\"", NULL);        // arg='"$var"'; cat $arg

  execlp("cat", "My File.txt", NULL);  // cat "$var"
  execlp("cat", "My File.txt", NULL);  // cat 'My File.txt'
  execlp("cat", "My File.txt", NULL);  // cat "My File.txt"
  execlp("cat", "My File.txt", NULL);  // cat My\ File.txt
  execlp("cat", "My File.txt", NULL);  // cmd=("cat" "$var"); "${cmd[@]}"
  execlp("cat", "My File.txt", NULL);  // arg="'My File.txt'"; eval "cat $arg"

Post by milkytron » Mon, Jun 26, 2017, 11:04 PM UTC

amelius wrote: post #58

bhaak wrote: post #13

How about you don't? Bash as scripting language is rather mediocre. Anything that is not simple in bash gets hard to read and debug and probably is wrong on some subtle levels. I have a rule of thumb that any shell script that grows beyond a screenful of lines gets redone in a proper scripting language.

Totally agree. Also, even if you manage to become better in Bash, you are bound to lose your skills at some point when you have been programming in other languages for a while. I always have to look up how to do even basic things in Bash. I just don't use it often enough for these things to "stick".