Replace substring in string

Question

i have just tried to one of my first bash scripts, i need to find a substring(after the ? part) in a url and replaced with the replace_string,

  #!/bin/bash

url="https://example.com/tfzzr?uhg"
#       123456 ...


first= echo `expr index "$url" ?`
last= expr length $url
replace_string="abc"



part_to_be_replace = echo ${url:($first+1):$last}//dont know how to use variable here

substring(url,part_to_be_replace,replace_string)

It does not work, i was able to find only the first accurance of ?, and the length of the string

For the arithmetic to work, you would have to write `$((first+1))`. — user1934428, Dec 01 '21 at 08:48
Your code has multiple syntax errors. Try http://shellcheck.net/ before asking for human assistance. — tripleee, Dec 01 '21 at 09:14
Tangentially see also [useless use of `echo`](https://www.iki.fi/era/unix/award.html#echo) — tripleee, Dec 01 '21 at 09:16

score 2 · Accepted Answer · answered Dec 01 '21 at 01:08

2

Does this help?

url="https://example.com/tfzzr?uhg"
replace_string="abc"

echo "${url}"
https://example.com/tfzzr?uhg

echo "${url//\?*/${replace_string}}"
https://example.com/tfzzrabc

# If you still want the "?"
echo "${url//\?*/\?${replace_string}}"
https://example.com/tfzzr?abc

See https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html for further details.

answered Dec 01 '21 at 01:08

jared_mamrot

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thank you very much your help this solutions is also works well – Andrewboy Dec 01 '21 at 01:17

score 1 · Answer 2 · answered Dec 01 '21 at 01:09

1

Use parameter expansion:

#! /bin/bash

url='https://example.com/tfzzr?uhg'
replace_string=abc

new=${url%\?*}?$replace_string
echo "$new"

${url%\?*} removes the pattern (i.e. ? and anything following it) from $url. ? needs to be quoted, otherwise it would match a single character in the pattern. Double the percent sign to remove the longest possible substring, i.e. starting from the first ?.

answered Dec 01 '21 at 01:09

choroba

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thank you very much your help, its works great, my minds just can not accept bashscripts sysntax,thank you for the very well detailed answer – Andrewboy Dec 01 '21 at 01:16

Replace substring in string

2 Answers2