How to reorder command line arguments in a script?

JASlinux · 02-23-2023, 06:17 AM

Imagine a file compression utility called compressor.

syntax: compressor [compression level] [archive name] [files to add]

On the command line I want to enter the compression level LAST.

example:

Code:

compressor newarchive.comp *.txt 9

[maximum compression]

How do I assign those variables in the correct order in Bourne?

pan64 · 02-23-2023, 06:22 AM

see the commands shift, the variable $# and here: https://opensource.com/article/18/5/...ro-bash-arrays (for example)

teckk · 02-23-2023, 09:42 AM

Bash example:

Code:

#!/usr/bin/bash

#Help
Help() {
    echo "
    Syntax: "$0" <file>
    Optional: "$0" [ -a -c -f -h ]

    Options:
    -a archive name
    -c Compression level: Options are 1 2 3 4
    -f Input files, \"Quote multiple file names\"
    -h This help menu
    "
}

#Get opts from switches
while getopts a:c:f:h option; do
    case "${option}" in
        a)  archive=${OPTARG} ;;
        c)  compression=${OPTARG} ;;
        f)  files=${OPTARG} ;;
        h)  Help; exit ;;
        *)  echo "Unknown switch"; exit ;;
    esac
done

echo "You entered: "$0" -a "$archive" -f "$files" -c "$compression""

Code:

./getopts.sh -a foo -f "one two three" -c 2
You entered: getopts.sh -a foo -f one two three -c 2

MadeInGermany · 02-23-2023, 10:59 AM

The usual order is "options first, filenames last", for a good reason.

Ok, for an exercise.

The shift command shifts out the FIRST argument not the last

The positional parameters could be copied to an array, where elements can be deleted at any position.
But you said Bourne shell? It does not have arrays

A brain teaser.

MadeInGermany · 02-23-2023, 11:42 AM

Found a solution, works in all Posix-compatible shells.

Code:

#!/bin/sh
n=$#
while [ $((n-=1)) -gt 0 ]
do
  set -- "$@" "$1"
  shift
done
echo "args":
printf "%s\n" "$@"
echo
echo compressor "$@"

JASlinux · 02-23-2023, 10:00 PM

Quote:

Originally Posted by MadeInGermany

But you said Bourne shell? It does not have arrays

.sh are Bourne, no?

Code:

#!/bin/sh

is same so I believe it is a standard script.

I will experiment & report results. It appears more complicated than I expected.

I realized even if we assign variables names (=), a script will place them in the order given on the command line without manipulation.

chrism01 · 02-23-2023, 11:05 PM

Once you go beyond one or 2 args, it's good idea to use something like getopts, as shown by teckk.
You need to ensure that even you can't get the 'order' wrong ..

MadeInGermany · 02-24-2023, 01:48 AM

.sh should be standard shell or Posix shell.
All current shells are compliant, some have more individual features (e.g. arrays).

The Bourne shell came with Unix SysV before there was a standard.
It had some bugs and design flaws. Unix Vendors started with individual fixes.
The standard has standardized the fixes, and added a few features (e.g. integer arithmetic).

evo2 · 02-24-2023, 02:24 AM

Quote:

Originally Posted by MadeInGermany

Found a solution, works in all Posix-compatible shells.

Code:

#!/bin/sh
n=$#
while [ $((n-=1)) -gt 0 ]
do
  set -- "$@" "$1"
  shift
done
echo "args":
printf "%s\n" "$@"
echo
echo compressor "$@"

Does the following not work?

Code:

#!/bin/sh
c="$1"
shift
echo compressor "$@" "$c"

Evo.

pan64 · 02-24-2023, 03:09 AM

Quote:

Originally Posted by evo2

Does the following not work?

Code:

#!/bin/sh
c="$1"
shift
echo compressor "$@" "$c"

Evo.

I guess we need the reverse direction, so pick the last argument (also remove it) and put it in front of the others.
The question is if we need bourne shell or we can use bash here.

MadeInGermany · 02-24-2023, 03:11 AM

@evo2 That puts the first argument last.
I think the goal is to put the last argument first.

evo2 · 02-24-2023, 05:53 PM

Quote:

Originally Posted by MadeInGermany

@evo2 That puts the first argument last.
I think the goal is to put the last argument first.

Really? OP posted:

Quote:

Originally Posted by JASlinux

On the command line I want to enter the compression level LAST.

Evo2.

evo2 · 02-24-2023, 05:56 PM

Quote:

Originally Posted by pan64

I guess we need the reverse direction, so pick the last argument (also remove it) and put it in front of the others.

Really? OP posted:

Quote:

Originally Posted by JASlinux

syntax: compressor [compression level] [archive name] [files to add]

On the command line I want to enter the compression level LAST.

Evo2.

michaelk · 02-24-2023, 06:19 PM

Quote:

Imagine a file compression utility called compressor.
syntax: compressor [compression level] [archive name] [files to add]

On the command line I want to enter the compression level LAST.

compressor newarchive.comp *.txt 9

The OP wants to enter the compression level last for whatever reason and I assume like everyone else that the arguments have to be reordered using a script to match the required order. Since most existing compression utilities use some sort of command line argument option I would probably go with a default option similar to /etc/default.

astrogeek · 02-24-2023, 06:40 PM

Quote:

Originally Posted by michaelk

The OP wants to enter the compression level last for whatever reason ...

I have stayed out of this discussion waiting for someone to ask what that reason actually is, so this looks like a good point to ask it myself...

@OP: What, exactly, are you trying to accomplish by reordering those args? Please describe the intended use, including a description of the problem to be solved and how you think this will solve it.