BASH: test for a decimal number

Skaperen · 04-26-2022, 01:27 PM

what is the best way, in bash, to test if a string is a valid decimal number? hexadecimal number? octal? binary? a valid IP address? IPv4? IPv6? i would like to see one command ways.

i am thinking about making a tool to do this for bash scripting even though i have shifted over to Python for such things.

Grobe · 04-26-2022, 02:08 PM

Without having a ready-made solution, I'd suggest regular expression tests.

chrism01 · 04-27-2022, 01:16 AM

You could possibly use tricks from https://wiki.bash-hackers.org/syntax/pe to eg strip out any 'valid' chars and see if anything it left - if there is, that wasn't a valid decimal (or whatever)..

pan64 · 04-27-2022, 03:25 AM

Quote:

Originally Posted by Skaperen

what is the best way, in bash, to test if a string is a valid decimal number? hexadecimal number? octal? binary? a valid IP address? IPv4? IPv6? i would like to see one command ways.

i am thinking about making a tool to do this for bash scripting even though i have shifted over to Python for such things.

Do not do that. bash is not really capable/suitable to do decimal or hexadecimal (octal/binary) calculations. Obviously it can be implemented (in pure bash), but it will be extremely slow/inefficient - and therefore more or less useless.

rnturn · 04-29-2022, 10:32 PM

Quote:

Originally Posted by chrism01

You could possibly use tricks from https://wiki.bash-hackers.org/syntax/pe to eg strip out any 'valid' chars and see if anything it left - if there is, that wasn't a valid decimal (or whatever)..

That might work for some of the more simple checks. But a one liner to tell you that whether or not "300.300.300.300" (all valid characters) is a valid IPv4 address? Not likely. Someone told me not long ago that the regex for accurately validating an IPv6 address in all its wierd and wacky forms ("Standard, and Mixed, and Compressed... Oh my!") is several thousand characters long. That'd be a heck of a one-liner.

teckk · 04-30-2022, 07:45 AM

I'll play briefly

checkip4.sh

Code:

#!/usr/bin/bash

#Validate IP4 example

ips=(
    8.8.8.8
    a.b.c.d
    192.168.1.1
    0.0.0.0
    255.255.255.255
    255.255.255.256
    256.255.255.255
    192.168.0.1
    192.168.0
    127.0.0.1
    1234.123.123.123
    )

valid_ip() {
    local  ip=$1
    local  stat=1

    if [[ "$ip" =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
        OIFS=$IFS
        IFS='.'
        ip=($ip)
        IFS=$OIFS
        [[ ${ip[0]} -le 255 && ${ip[1]} -le 255 && ${ip[2]} -le 255 && ${ip[3]} -le 255 ]]
        stat=$?
    fi
    return $stat
}

for ip in "${ips[@]}"; do
    if valid_ip "$ip"; then 
        stat='good'
    else 
        stat='bad'; fi
    printf "%-20s: %s\n" "$ip" "$stat"
done

Skaperen · 04-30-2022, 05:18 PM

Quote:

Originally Posted by rnturn

That might work for some of the more simple checks. But a one liner to tell you that whether or not "300.300.300.300" (all valid characters) is a valid IPv4 address? Not likely. Someone told me not long ago that the regex for accurately validating an IPv6 address in all its wierd and wacky forms ("Standard, and Mixed, and Compressed... Oh my!") is several thousand characters long. That'd be a heck of a one-liner.

how can you test for write access to a file in one line? the "test -w" command can do that and give a result in the exit status. the reason i am asking this is to discover if it is worthwhile to make a new command to do such a test. so maybe "testnum -x $myhex" could do that.

note that bash can convert hexadecimal and octal to decimal in its arithmetic operation. i don't know how to trap the errors the a bad digit could cause. maybe someone here does.

i have written tests for IP4 and IP6 in Python as functions that let the C library do the hard work. testing numbers in various bases from 2 to 36 or beyond should be trivial in Python to make a command script. i'm thinking of:

Code:

testnum -b num
testnum -o num
testnum -d num
testnum -x num
testnum -4 addr
testnum -6 addr

michaelk · 04-30-2022, 06:07 PM

Quote:

how can you test for write access to a file in one line? the "test -w" command can do that and give a result in the exit status.

test is a shell built in function as well as a GNU core utility. The latter is a separate compiled program and works because that is how the utility was written. If it is worthwhile for you to have such a utility then who cares about what others think...

bash basically treats all variables as strings until you use them in a particular function or test which is why I assume that regex was suggested above. You could probably write your utility in just about any language but bash might not be the best choice.

rknichols · 04-30-2022, 07:06 PM

Quote:

Originally Posted by michaelk

You could probably write your utility in just about any language but bash might not be the best choice.

I would also recommend against trying to use Ook (for any purpose, for that matter). But hey, Ook is Turing-complete, so it's possible, in theory.

pan64 · 05-01-2022, 02:20 AM

Quote:

Originally Posted by Skaperen

how can you test for write access to a file in one line? the "test -w" command can do that and give a result in the exit status. the reason i am asking this is to discover if it is worthwhile to make a new command to do such a test. so maybe "testnum -x $myhex" could do that.

You can definitely implement it and put it into bash [source code] if you wish.

Quote:

Originally Posted by Skaperen

note that bash can convert hexadecimal and octal to decimal in its arithmetic operation. i don't know how to trap the errors the a bad digit could cause. maybe someone here does.

As you wrote a test (or convert) function will return 0 (as exit code) on success and return non-zero otherwise. What else do you need?

Quote:

Originally Posted by Skaperen

i have written tests for IP4 and IP6 in Python as functions that let the C library do the hard work. testing numbers in various bases from 2 to 36 or beyond should be trivial in Python to make a command script. i'm thinking of:

Code:

testnum -b num
testnum -o num
testnum -d num
testnum -x num
testnum -4 addr
testnum -6 addr

Additionally -p (positive), -n (negative), -f (float), -i (integer). What about scientific notations, complex numbers and others?

teckk · 05-01-2022, 08:57 AM

Quote:

i don't know how to trap the errors the a bad digit could cause. maybe someone here does.

If I understand you.

Code:

#!/usr/bin/bash

#Test for hex or numeric example

n=(12 31 ae 1a 16 b5 ff 1f 12 24 2c AA Ac 1C 39 28 1f 3d 10 29 a1 A2 a3)

is_numeric() {
    case "$i" in
        "" | *[![:digit:]]* | 0[[:digit:]]* ) return 1;;
    esac
}

is_hex() {
    case "$i" in
        "" | *[![:xdigit:]]* ) return 1;;
    esac
}

for i in "${n[@]}"; do
    if is_numeric; then
        echo ""$i" is numeric"
    elif is_hex; then
        echo ""$i" is hex"
    fi
done

michaelk · 05-01-2022, 11:30 AM

I think something more like...

Code:

#!/bin/bash
while getopts ":n:b:o:d:n:x:" options; do
   case "${options}" in
     n)
        mynum=${OPTARG}
        if ! [[ "$mynum" =~ ^[0-9]+$ ]] ; then
            echo "is not number"
            exit 1
        fi    
     ;;
     d)
        mynum=${OPTARG}
        if ! [[ "$mynum" =~ ^[+-]?[0-9]+([.,][0-9]+)?$ ]] ; then
            echo "not a decimal"
            exit 1
        fi 
    ;; 
    x)
        mynum=${OPTARG}
        if  ! [[ "$mynum" =~ ^[A-Fa-f0-9]+$ ]] ; then
            echo "is not hex"
            exit 1
        fi 
    ;;        
   esac
done

It depends on what or if you use some standard notation for octal or hex numbers...

pan64 · 05-01-2022, 11:50 PM

Quote:

Originally Posted by michaelk

I think something more like...

Code:

#!/bin/bash
while getopts ":n:b:o:d:n:x:" options; do
   case "${options}" in
     n)
        mynum=${OPTARG}
        if ! [[ "$mynum" =~ ^[0-9]+$ ]] ; then
            echo "is not number"
            exit 1
        fi

It depends on what or if you use some standard notation for octal or hex numbers...

regex is extremely slow in bash, also would be faster if implemented as function (and sourced)

Code:

function isint() {
    local mynum="$1"
    local a="${mynum//[0123456789]/}"
    [[ ${#a} -eq 0 ]]
}
function ishex() {
    local mynum="$1,,"
    local a="${mynum//[0123456789abcdef]/}"
    [[ ${#a} -eq 0 ]]
}

but you need to check additionally the decimal point, +- or any other "requirements". (not tested)

rknichols · 05-02-2022, 08:37 AM

How about numbers with an explicit base:

Code:

$ echo $((10#1234))
1234
$ echo $((0xbeef))
48879
$ echo $((21#20))
42

Skaperen · 05-03-2022, 02:50 PM

Quote:

Originally Posted by pan64

bash is not really capable/suitable to do decimal or hexadecimal (octal/binary) calculations.

it can, at least, do conversion from hexadecimal or octal to decimal.

Code:

lt2a/forums/1 /home/forums 13> bash -c 'echo $((0x11111111));echo $((011111111))'
286331153
2396745
lt2a/forums/1 /home/forums 14>

Quote:

Originally Posted by pan64

Obviously it can be implemented (in pure bash), but it will be extremely slow/inefficient - and therefore more or less useless.

agreed. but if i can trap errors correctly, maybe trying a conversion could be a way to test for validity without all that slow/inefficient.