Using sed to substitute different values

brh1 · 08-27-2018, 03:33 PM

Good day.

I've been trying to find a method to substitute values strings of different lengths using sed. Using grep I search for an entry followed by an equal sign after which I want to replace all digits or letters.

Shown below, in my case I want to change MAXDAYS=300 to MAXDAYS=90, however the original could be anything.

I have tried the following:

Code:

sed -i -e 's/^MAXDAYS=[0-9]/MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS=[0..9]/MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS={?}/MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS={.}/MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS=./MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS=*/MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS={*}/MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS=\{.\}/MAXDAYS=90/' SystemHardening.cfg
sed -i -e 's/^MAXDAYS=\{*\}/MAXDAYS=90/' SystemHardening.cfg

Any hints or tips appreciated.

Bjoern

BW-userx · 08-27-2018, 03:50 PM

test file

Code:

MAXDAYS=900
MAXDAYS=20000

sed

Code:

sed -i -e 's|MAXDAYS=.*|MAXDAYS=90|' maxdays

results

Code:

MAXDAYS=90
MAXDAYS=90

MadeInGermany · 08-27-2018, 05:23 PM

The following avoids the repetition of the search key

Code:

sed -i '/^MAXDAYS=/ s/=.*/=90/' SystemHardening.cfg

syg00 · 08-27-2018, 06:40 PM

Better in both cases to use [:alnum:] class to ensure the original request is properly resolved. Also retains any following data - say a comment - if it exists.

scasey · 08-27-2018, 06:50 PM

Quote:

Originally Posted by MadeInGermany

The following avoids the repetition of the search key

Code:

sed -i '/^MAXDAYS=/ s/=.*/=90/' SystemHardening.cfg

MadeInGermany...would you mind explaining that syntax...new stuff for me. I'd have done it the way BW-userx did.

scasey · 08-27-2018, 06:55 PM

Quote:

Originally Posted by syg00

Better in both cases to use [:alnum:] class to ensure the original request is properly resolved. Also retains any following data - say a comment - if it exists.

I get how that's more specific than .*, but given the use case, shouldn't it be [:digit:]...the OP only wants to replace numbers.

Not criticizing...asking to learn.

syg00 · 08-27-2018, 07:01 PM

Read the OP.

BW-userx · 08-27-2018, 07:03 PM

I'd think it'd still need to have that requirement of "MAXDAYS" or even just the "=" for the search pattern , and not just numbers being all changed to 90.

scasey · 08-27-2018, 07:34 PM

Quote:

Originally Posted by syg00

Read the OP.

Ahh!

Quote:

replace all digits or letters

Got it.

brh1 · 08-27-2018, 10:44 PM

Quote:

Originally Posted by BW-userx

test file

Code:

MAXDAYS=900
MAXDAYS=20000

sed

Code:

sed -i -e 's|MAXDAYS=.*|MAXDAYS=90|' maxdays

results

Code:

MAXDAYS=90
MAXDAYS=90

Thank you BW, works like a charm.

Bjoern

scasey · 08-28-2018, 12:55 AM

You can mark this thread "Solved" using the Thread Tools at the top of the thread.

MadeInGermany · 08-29-2018, 08:20 AM

Quote:

Originally Posted by scasey

MadeInGermany...would you mind explaining that syntax...new stuff for me. I'd have done it the way BW-userx did.

Code:

/key/ s/old/new/

substitutes old by new if key is found.