Using SED within a shell to replace pattern in desired files

Question

I have a bash shell script written as below:

#!/bin/bash
#arg1: pattern to be found
#arg2: pattern to be replaced
#arg3: filename pattern
echo replace $1 by $2 for all $3 files
for  i in `find . -type f -name "$3"`
do
sed  's/$1/$2/g' $i
done

I use this script (say, called SUBS) as:

./SUBS bbb ddd aa

where the file aa has:

aaaa
bbbb
cccc

But, while I expect to see bbbb replaced as dddb, it shows the same content i.e. bbbb. Any clue what is wrong here? Also, I would like to make the same file getting modified after the replacement. How can I do that? This Qs is little similar to sed substitution with bash variables, but in my Qs, I have used a pattern to find and replace as argument to the shell variable.

heemayl · Accepted Answer · 2016-04-06T12:41:46.120

3

Variables won't expand when put inside single quotes; you need to use double quotes:

sed "s/$1/$2/g" "$i"

To modify the file in place:

sed -i.bak "s/$1/$2/g" "$i"

After the operation the original file will be backed up with .bak extension; if you don't want to keep backup:

sed -i "s/$1/$2/g" "$i"

edited Apr 06 '16 at 12:41

answered Apr 06 '16 at 12:25

heemayl

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Many thanks. I would like to make the same file getting modified after the replacement. How can I do that? It's displaying on stdout now – Dr. Debasish Jana Apr 06 '16 at 12:39
@Dr.DebasishJana Check my edits.. – heemayl Apr 06 '16 at 12:41
I am using Solaris, where sed -i is not supported, any other option? – Dr. Debasish Jana Apr 06 '16 at 12:43
@Dr.DebasishJana I don't have Solaris so can't tell..although you can use redirection: `sed "s/$1/$2/g" "$i" >"$i".bak && mv "$i".bak "$i"` – heemayl Apr 06 '16 at 12:52
That's nice, this would do – Dr. Debasish Jana Apr 06 '16 at 12:58

Using SED within a shell to replace pattern in desired files

1 Answers1