Sed error : bad option in substitution expression

Question

I have a configuration file (gpsd.default) containing data with the following format:

# If you must specify a non-NMEA driver, uncomment and modify the next line     
GPSD_SOCKET="/var/run/gpsd.sock"                                                
GPSD_OPTIONS=""                                                                
GPS_DEVICES=""

I am making a change on the file with sed:

sed -i 's/^GPS_DEVICES="".*/GPS_DEVICES="dev/ttyUSB1"/' /etc/default/gpsd.default
or 
sed -i '4s/^.*/GPS_DEVICES="dev/ttyUSB1"/' /etc/default/gpsd.default

The above sed command returns error:

sed: bad option in substitution expression

Because the new line contains "/" in its expression.

How to update my sed command to make it work?

The `/` isn't your only potential problem, see http://stackoverflow.com/questions/29613304/is-it-possible-to-escape-regex-metacharacters-reliably-with-sed/29626460#29626460 — Ed Morton, May 05 '15 at 15:10

score 40 · Answer 1 · edited May 05 '15 at 11:56

40

This is because you are using a regex containing /, which is the same character sed uses as delimiter.

Just change the sed delimiter to another one, for example ~:

sed -i 's~^GPS_DEVICES="".*~GPS_DEVICES="dev/ttyUSB1"~' /etc/default/gpsd.default

By the way, since you are changing files in /etc, you may want to use -i.bak, so that the original file gets backed up. It is a good practice to prevent loss of important information.

edited May 05 '15 at 11:56

user3439894

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answered May 05 '15 at 10:51

fedorqui

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It is practice if it is being used as a noun :) – May 05 '15 at 11:12
1

@fedorqui You could just escape the `/ `like `\/` – Jahid May 05 '15 at 16:21
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@Jahid yes, true, but it is neater to use another delimiter. – fedorqui May 05 '15 at 16:25
For this particular case, yeah, but what would you do if you wanted to match `~` ? – Jahid May 05 '15 at 16:28
@Jahid there is no definitive solution for this. Neither escaping nor using another delimiter solves all the situations, so it is a matter to see what suits best in each case. – fedorqui May 05 '15 at 19:21

score 4 · Answer 2 · answered May 05 '15 at 10:53

4

You should update your sed command to this.

sed -i 's/^GPS_DEVICES=\"\".*/GPS_DEVICES=\"dev\/ttyUSB1\"/' /etc/default/gpsd.default

answered May 05 '15 at 10:53

Harshad Yeola

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Sed error : bad option in substitution expression

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