Replacing string in a file with script

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, Mar 30 '19 at 22:57
Do you have any suggestions on how to fend off the issue regarding magic characters? Thank you! — Sphery, Mar 30 '19 at 23:09

score 1 · Accepted Answer · answered Mar 30 '19 at 23:05

1

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.

answered Mar 30 '19 at 23:05

Zeitounator

1 Answers1