Re: a sed question

 Salvador Mirzo <smirzo@example.com>:

Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
>

On 18.12.2024 20:46, Salvador Mirzo wrote:
>
First (before I forget it) change your string comparison '<' to the
numerical comparison operator '-lt' as in:   test $# -lt 2 && usage
Otherwise, if you get used to using the wrong operator, you may get
subtle errors in future if you continue that habit.

>
Changed.  Why is it the wrong operator?

 '<' compares two strings lexically, whereas '-lt' compares two  numbers numerically.  Some examples:
 1 < 2 ==> true
 2 < 2 ==> false
 3 < 2 ==> false
 10 < 2 ==> true, probably not your intention.
 1 -lt 2 ==> true
 2 -lt 2 ==> false
 3 -lt 2 ==> false
 10 -lt 2 ==> false

It seems it's not the standard one---checking just now on the
POSIX.1 spec.

 The recent POSIX standard knows of the '<' operator, see
 <https://pubs.opengroup.org/onlinepubs/9799919799/utilities/test.html#tag_20_121_05>.

Also note that using $* may not work correctly (e.g. depending on
filenames [containing spaces] used). The safe form is a quoted  "$@"

>
I learned something here.
>
--8<-------------------------------------------------------->8---
$ cat script.sh
#!/bin/sh
echo dollar-star $*
./script dollar-star $*
>
echo quoted-dollar-star "$*"
./script "$*"
>
echo dollar-at $@
./script $@
>
echo quoted-dollar-at "$@"
./script "$@"
>
$ cat script.c
#include <stdio.h>
>
int main(int argc, char *argv[]) {
  printf("\nfull cmdline: ");
  for (int i = 0; i < argc; ++i) {
    printf("%s ", argv[i]);
  }
  printf("\nargs: %d\n", argc);
  for (int i = 0; i < argc; ++i) {
    printf("arg %d: %s\n", i, argv[i]);
  }
  return 0;
}
--8<-------------------------------------------------------->8---
>
$ ./script.sh 1 2 "th ree"
dollar-star 1 2 th ree
>
full cmdline: ./script dollar-star 1 2 th ree
args: 6
arg 0: ./script
arg 1: dollar-star
arg 2: 1
arg 3: 2
arg 4: th
arg 5: ree
quoted-dollar-star 1 2 th ree
>
full cmdline: ./script 1 2 th ree
args: 2
arg 0: ./script
arg 1: 1 2 th ree
dollar-at 1 2 th ree
>
full cmdline: ./script 1 2 th ree
args: 5
arg 0: ./script
arg 1: 1
arg 2: 2
arg 3: th
arg 4: ree
quoted-dollar-at 1 2 th ree
>
full cmdline: ./script 1 2 th ree
args: 4
arg 0: ./script
arg 1: 1
arg 2: 2
arg 3: th ree
$

 So using "$@" is the only way to have the shell pass its  positional parameters unmodified (i. e. neither glued together  nor split at internal white space (more precise: split according  to the contents of the IFS shell parameter)) to commands it  invokes.