mjhjmtu

SED command not replacing in bash under Debian, but works in command line.

Works in command line:

sed -i 's|/dev/disk/by-label/SR6D4|/dev/disk/by-label/SR4D4|g' /etc/my/config.xml

Not working in bash script, does not replace the string:

from="SR6D4"
to="SR4D4"
path_from="/dev/disk/by-label/$from"
path_to="/dev/disk/by-label/$to"
echo "sed -i 's|$path_from|$path_to|g' $file"
sed -i 's|$path_from|$path_to|g' $file

Why doesn't replace string in file when using sed in bash?

Shell variables won't get expanded in single quotes. (It's kind of what single quotes are for.)

sed -i "s|$path_from|$path_to|g" "$file"

should work better. (I've added double quotes around $file just in case your filename ever contains spaces.)

As mentioned earlier you have problem with quoting. But there are some opinions about string replacement in file. See below.

It's bad idea to replace string in file because it's unsafety. There is small probability to lost file's data while changing.

You could try to backup file before changing:

cp /path/to/file,.backup
sed -i 'place your pattern here' /path/to/file

and you will get file with name file.backup.

You need to remember: if your file will be damaged and you will delete and replace it - file will have different inode and will lost all hard links.

The second safety method:

mv /path/to/file,.backup; 
cat /path/to/file.backup | sed 'place your pattern here' > /path/to/file

The next point. As bashFAQ thinks:

Embedding shell variables in sed commands is never a good idea

Thats why you need to use awk with -v options instead. Your script may look like this:

from="SR6D4"
to="SR4D4"
path_from="/dev/disk/by-label/$from"
path_to="/dev/disk/by-label/$to"
sed -i 's|$path_from|$path_to|g' $file
mv $file,.backup
cat "$file.backup" | awk -v awkfrom="$path_from" -v awkto="$path_to" 'gsub(awkfrom,awkto)' > $file