如何替换参数的值

Question

How can I replace the values of parameters step by step.

What I mean is,

For Example- Url is https://example.com/?p=first&q=second&r=third

First I want to add '123' on p param https://example.com/?p=123&q=second&r=third

Then again with same URL but different parameter, such as q param https://example.com/?p=first&q=123&r=third

Again with same URL but different parameter,

https://example.com/?p=first&q=second&r=123

What I tried:

while read line; do
first_part=`echo $line | cut -d'=' -f1`                                          second_part=`echo $line | cut -d'=' -f2`

    echo "${first_part}=123${second_part}"

    echo "${first_part}${second_part}=123"

done < urls.txt

Answer 1

The problem described is a good application for AWK's capabilities. The demo script includes samples for both URLs and a mapping functions file for global transformation of URLs.

This approach allows for parameters to "free float", not dependent on matching at a specific sequential position in the URL string.

This approach also allows for parameters to be strings of any length.

#!/bin/bash

#QUESTION:  https://stackoverflow.com/questions/75124190/how-to-replace-the-values-of-a-param

cat >URL.list <<"EnDoFiNpUt"
https://example.com/?p=first&q=second&r=third
https://example.com/?r=zinger
https://example.com/?r=bonkers&q=junk&p=wacko
https://example.com/?p=flyer
EnDoFiNpUt

cat >mapfile.txt <<"EnDoFiNpUt"
q=SECOND
r=THIRD
p=FIRST
EnDoFiNpUt

awk -v datFile="mapfile.txt" 'BEGIN{
    ## Initial loading of the mapping file into array for comparison
    split( "", transforms ) ;
    indexT=0 ;
    while( getline < datFile ){
        indexT++ ;
        transforms[indexT]=$0 ;
    } ;
}
{
    ### Split off beginning of URL from parameters
    qPos=index( $0, "?" ) ;
    beg=substr( $0, 1, qPos ) ; 

    ### Load URL elements into array for comparison
    rem=substr( $0, qPos+1 ) ;
    n=split( rem, parts, "&" ) ;

    ### Match and Map transforms elements with URL parts
    for( k=1 ; k<= indexT ; k++ ){
        dPos=index( transforms[k], "=" ) ;
        fieldPref=substr( transforms[k], 1, dPos ) ;
        for( i=1 ; i<=n ; i++ ){
            if( parts[i] ~ fieldPref ){
                parts[i]=transforms[k] ;
            } ;
        } ;
    } ;

    ### Print transformed URL
    printf("%s%s", beg, parts[1] ) ;
    for( i=2 ; i<=n ; i++ ){
        printf("&%s", parts[i] ) ;
    } ;
    print "" ;
}' URL.list

The output looks like this:

https://example.com/?p=FIRST&q=SECOND&r=THIRD
https://example.com/?r=THIRD
https://example.com/?r=THIRD&q=SECOND&p=FIRST
https://example.com/?p=FIRST

Answer 2

HTML params are, by spec, orderless, so you can simply place p= 's new value at the tail instead of original position:

echo 'https://example.com/?p=first&q=second&r=third' | 

 mawk NF=NF FS='p=[^&]*[&]?' OFS= ORS='&p=123\n'

     1  https://example.com/?q=second&r=third&p=123

same for q= .

if you're modifying r= instead, then set both FS and OFS to "=" , and do it it like a vanilla value update for $NF