[SOLVED] How can I replace a string based on a pattern on a line?

geekoo · 08-20-2022, 02:37 AM

Hi

I have a line in a file with this string

usb04 Dodge City (1939)

I want to change usb04 to usb03 if the line contains the pattern Dodge City.

There are many lines in the file with usb04. I only want to change one only.

I did a google search on this but I get results contrary to what I want.

eg sed 's/usb03/Dodge City/' videos

This is NOT what I want. This will change Dodge City to usb03.

I want to change usb04 to usb03 if the line has the pattern Dodge City.

Is that possible with sed, awk or other command? Thanks

allend · 08-20-2022, 02:55 AM

Quote:

Is that possible with sed, awk or other command?

Yes.

syg00 · 08-20-2022, 03:09 AM

That link has pretty good explanation, but you would be better served to learn e.g. sed (or awk or whatever) rather than just asking for particular answers to a one-off problem.
Both are well documented.

pan64 · 08-20-2022, 03:59 AM

Quote:

Originally Posted by geekoo

I want to change usb04 to usb03 if the line has the pattern Dodge City.

I did a google search on this but I get results contrary to what I want.

eg sed 's/usb03/Dodge City/' videos

This is NOT what I want. This will change Dodge City to usb03.

No, that is wrong. that will change usb03 to Dodge City.

Anyway, the link has a very good example.

Quote:

Originally Posted by geekoo

Is that possible with sed, awk or other command?

Yes, definitely, almost any language can do that (including bash, java, perl, python, ruby, c, ....). And also there are several different ways to solve it.

Code:

sed 's/usb04 Dodge City/usb03 Dodge City/'

geekoo · 08-20-2022, 04:27 AM

Thanks guys

I got it.

I tried it first.

Code:

sed '/Dodge City/s/usb04/usb03/' videos

It did what I wanted and I committed the change by adding sed -i

I just click yes on all replies as helpful answers. Thanks allend for pointing me to the source to learn it.

syg00 · 08-20-2022, 05:30 AM

Quote:

Originally Posted by geekoo

It did what I wanted and I committed the change by adding sed -i

Be aware that this has the potential to destroy your file. Fine if you check it is ok first, but better perhaps to include a suffix to ensure a backup is created automatically for you.

geekoo · 08-20-2022, 06:28 AM

Quote:

Originally Posted by syg00

Be aware that this has the potential to destroy your file. Fine if you check it is ok first, but better perhaps to include a suffix to ensure a backup is created automatically for you.

That's a great tip.

teckk · 08-20-2022, 10:11 AM

Quote:

I want to change usb04 to usb03 if the line contains the pattern Dodge City.

You could also do that with regex.

Code:

a="usb04 Dodge City (1939)"

#a="usb04 Doge City (1939)"

if [[ "$a" == *"Dodge City"* ]]; then
    echo ${a//usb04/usb03};
else
    echo "$a"
fi

MadeInGermany · 08-20-2022, 01:27 PM

With bash imternals you need a while-read loop to also process the other lines

Code:

while IFS= read -r line
do
  if [[ "$line" == *"Dodge City"* ]]; then
    printf "%s\n" "${line//usb04/usb03}";
  else
    printf "%s\n" "$line"
  fi
done < inputfile > outputfile

geekoo · 08-21-2022, 01:30 AM

Quote:

Originally Posted by teckk

You could also do that with regex.

Code:

a="usb04 Dodge City (1939)"

#a="usb04 Doge City (1939)"

if [[ "$a" == *"Dodge City"* ]]; then
    echo ${a//usb04/usb03};
else
    echo "$a"
fi

Quote:

Originally Posted by MadeInGermany

With bash imternals you need a while-read loop to also process the other lines

Code:

while IFS= read -r line
do
  if [[ "$line" == *"Dodge City"* ]]; then
    printf "%s\n" "${line//usb04/usb03}";
  else
    printf "%s\n" "$line"
  fi
done < inputfile > outputfile

Thanks guys for the extra info. However, it's alot of code to write where I can do the same with a sed one-liner.

but it's good to know.

geekoo · 08-21-2022, 01:56 AM

Does anyone know how to make Dodge City case insensitive in the search?

I purposely changed Dodge City to lowercase to test case insensitive, but it's not working.

I tried with the i switch (red) in two locations but it doesn't work.

Code:

$ sed '/Dodge City/s/usb04/usb03/i' videos
usb04 	dodge city (1939)

$ sed '/Dodge City/is/usb04/usb03/' videos
usb04 	dodge city (1939)

How can I make Dodge City be case sensitive? The link doesn't show how. Thanks

geekoo · 08-21-2022, 02:22 AM

I got it. To make Dodge City case insensitive. I had to use a capital I, not a lowercase i.

Code:

$ sed '/Dodge City/Is/usb04/usb03/' videos
usb03 	dodge city (1939)

syg00 · 08-21-2022, 03:05 AM

I'd suggest you go here and download the sed manual in your preferred format. It is a reference, but also has examples to explain functionality.

geekoo · 08-21-2022, 04:39 AM

Quote:

Originally Posted by syg00

I'd suggest you go here and download the sed manual in your preferred format. It is a reference, but also has examples to explain functionality.

This is very helpful. Thanks