Bash命令rev以反转删除者

Question

I am working on a shell script that converts exported Microsoft in-addr.apra.txt files to a more useful format so that i can use it in the future in other products for automation purposes. No i am figuring a problem which (im not a programmer) can not solve in a simple way.

Sample script

x=123.223.224
rev $x

gives me

422.322.321

but i want to have the output as follow:

224.223.123

is there a easy way to do it without rev or putting each group in a variable? Or is there a sample i can use? or maybe i use the wrong tools to do it?

Answer 1

Using awk :

x='123.223.224'
awk 'BEGIN{FS=OFS="."} {for (i=NF; i>=2; i--) printf $i OFS; print $1}' <<< "$x"
224.223.123

Answer 2

Use awk for this!

If your text file always contains three octets, simply use . as separator:

echo $x | awk -F. '{ print $3 "." $2 "." $1 }'

For more complex cases, use internal split() :

echo $x | awk '{ 
    n = split($0, a, "."); 
    for(i = n; i > 1; i--) { 
        printf "%s.", a[i]; 
    } 
     print a[1]; }'

In this sample split() will split every line (which is passed as argument $0 ) using delimiter . , saves resulting array into a and returns length of that array (which is saved to n ). Note that unlike C, split() array indexes are starting with one.

Or python :

python -c "print '.'.join(reversed('$x'.split('.')))"

Answer 3

Here is my script.

#!/bin/sh

value=$1
delim=$2
total_fields=$(echo "$value" | tr -cd $2 | wc -c)

let total_fields=total_fields+1

i=1


reverse_value=""
while [ $total_fields -gt 0 ]; do

        cur_value=$(echo "$value" | cut -d${delim} -f${total_fields})
        if [ $total_fields -ne 1 ]; then
                cur_value="$cur_value${delim}"
        fi
        #echo "$cur_value"
        reverse_value="$reverse_value$cur_value"

        #echo "$i --> $reverse_value"

        let total_fields=total_fields-1
done

echo "$reverse_value"

Answer 4

使用一些小工具。

tr '.' '\n' <<< "$x" | tac | paste -sd.

224.223.123