Replacing string in a file with script [duplicate]

Question

One of the ways replacing a string with sed can be done as follows:

sed -i 's/old_str/new_str/' file.txt

However if replace.sh is

 sed -i 's/$1/$2/' $3

the command ./replace.sh old_str new_str file.txt doesn't seem to work -- after making replace.sh executable of course. Why is that?

I am aware rpl does exactly the same as I intend to do with replace.sh, but I'd like to understand why is it not working.

You're hitting a quoting issue. The single quote ' character prevents $1 from being expanded and you have the literal string $1. If you use "" instead then it'll work... but beware of magic characters in a solution like this; ./replace.sh my/string new/stuff myfile won't work! — Stephen Harris, CommentedMar 30, 2019 at 22:57
Do you have any suggestions on how to fend off the issue regarding magic characters? Thank you! — Sphery, CommentedMar 30, 2019 at 23:09

Zeitounator · Accepted Answer · 2019-03-30 23:05:35Z

There is no parameter expansion inside single quotes (see this previous answer on stackoverflow)

toto=1 echo '$toto' > $toto echo "$toto" > 1

Simply replace your single quotes with double quotes and your script will do what you expect.

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