4 ms·

You don't need any of those `exec`s. Yes, GNU grep has `-a`. If you don't like the backslash-newline-pipe sequence, if you put the pipe at the end of the previ

by LukeShu 10y ago

You don't need any of those `exec`s. Yes, GNU grep has `-a`. If you don't like the backslash-newline-pipe sequence, if you put the pipe at the end of the previous line, you don't need the backslash; but it's less obvious that the next line is operating on the output of the previous. Multi-line arguments to sed can be a pain (good luck getting your editor to auto-indent them). Instead, you can use -e to specify multiple sed commands. There's nothing in there that would make it not work in bash. That should work in any Bourne-family shell. It only handles 0 or 1 arguments correctly, not > 1.

_c_ 10y ago
Thanks for taking the time to comment. Multiple arguments could be added if you want that. I personally do not need it as I search the cmdline patterns I need without using spaces. I use dots instead. Quick and dirty. I write 100's of these small scripts for my own use only so I have my own style, peculiar as it may be. I never need indentation because I always keep scripts short; I only use it occasionally and randomly. I do not use -e with sed, unless I'm using branches or loops. The execs seem superfluous but actually make a difference, at least on the UNIX I use. Try it with and without and see if you notice. All my scripts are portable to Bash, but they're also portable to the most basic of Bourne-compatible shells too. I do not use Bash.
- LukeShu 10y ago
  What shell are you using? I could see a naive shell forking twice without exec, but I don't know of a shell that does that. Exec just says "don't fork(3) before calling exec(3)", but, but inside of a pipeline like that, it shouldn't fork again anyway. I have tried it with and without.
  - _c_ 10y ago
    In theory it should not make a difference but my scripts seem to run faster when I use exec after pipe. Normally I would only add exec to the last command in the script, as djb does. But then I started experimenting with using it after pipes. If you or anyone can explain why this could make scripts "seem" to execute faster, I would be grateful. Here's the shell source: ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-release-7/src/bin/sh Incidentally, have you ever tried execlineb? I use that sometimes too.

by LukeShu 10y ago

_c_ 10y ago

Thanks for taking the time to comment. Multiple arguments could be added if you want that. I personally do not need it as I search the cmdline patterns I need without using spaces. I use dots instead. Quick and dirty. I write 100's of these small scripts for my own use only so I have my own style, peculiar as it may be. I never need indentation because I always keep scripts short; I only use it occasionally and randomly. I do not use -e with sed, unless I'm using branches or loops. The execs seem superfluous but actually make a difference, at least on the UNIX I use. Try it with and without and see if you notice. All my scripts are portable to Bash, but they're also portable to the most basic of Bourne-compatible shells too. I do not use Bash.

LukeShu 10y ago
What shell are you using? I could see a naive shell forking twice without exec, but I don't know of a shell that does that. Exec just says "don't fork(3) before calling exec(3)", but, but inside of a pipeline like that, it shouldn't fork again anyway. I have tried it with and without.
- _c_ 10y ago
  In theory it should not make a difference but my scripts seem to run faster when I use exec after pipe. Normally I would only add exec to the last command in the script, as djb does. But then I started experimenting with using it after pipes. If you or anyone can explain why this could make scripts "seem" to execute faster, I would be grateful. Here's the shell source: ftp://ftp.netbsd.org/pub/NetBSD/NetBSD-release-7/src/bin/sh Incidentally, have you ever tried execlineb? I use that sometimes too.