Sed command to find the line containing a string and replacing part of it

Question

I have a file, which should have an entry like this -

'new_revision': '111c1110b08b96c987482e08d28d84ea3d777egh',

I want to find this line and replace it with something like this

'new_revision': '000c0000b08b96c987482e08d28d84ea3d777eml',

I tried commands like-

sed -i 's/'new_revision': ''([a-z0-9]{40})''/'new_revision': '000c0000b08b96c987482e08d28d84ea3d777eml'/' file

But doesn't work properly and gives error as no matches found.

Welcome to SO, good that you have shared your efforts(keep it up). Could you please do confirm if this is a json file? — RavinderSingh13
– RavinderSingh13, Commented Sep 21, 2022 at 5:03

The fourth bird · Accepted Answer · 2022-09-20 19:17:18Z

1

You could use -E and wrap the sed command in double quotes and use the capture group in the first part, using a backreference \1 in the replacement.

sed -E s/"('new_revision': ')[a-z0-9]{40}'/\1000c0000b08b96c987482e08d28d84ea3d777eml'/" file

Output

'new_revision': '000c0000b08b96c987482e08d28d84ea3d777eml',

edited Sep 20, 2022 at 19:17

answered Sep 20, 2022 at 19:15

The fourth bird

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Comments

William Pursell · Accepted Answer · 2022-09-20 20:32:59Z

1

You don't want to do the search and replace on every line, you only want to do it on the lines that match. In other words, you should restrict the lines on which the s command is run with an address. eg:

$ new_hash=000c0000b08b96c987482e08d28d84ea3d777eml
$ sed "/^'new_revision':/s/'[^']*',$/'$new_hash'/" input

answered Sep 20, 2022 at 20:32

William Pursell

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1 Comment

stevesliva Over a year ago

I do find myself wondering if there's that optimization in the code... to recognize /fixedstring/ and run it faster than s/fixedstring .*/fixedstring new/

Ed Morton · Accepted Answer · 2022-09-21 11:13:18Z

1

awk -v tag="'new_revision':" -v val="'000c0000b08b96c987482e08d28d84ea3d777eml'," '$1==tag{$2=val} 1' file
'new_revision': '000c0000b08b96c987482e08d28d84ea3d777eml',

edited Sep 21, 2022 at 11:13

answered Sep 21, 2022 at 0:01

Ed Morton

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2 Comments

aggsol Over a year ago

OP is asking for a sed command. While being an alternative some context and explanation would help future readers.

Ed Morton Over a year ago

@aggsol If we only provided sed commands when people ask for sed commands then we'd be doing the askers a great dis-service as people ask for what they know and/or think they need which often is different from what is the right way to do something.. If you look at the top answerers of the sed tag, stackoverflow.com/tags/sed/topusers, you'll notice my name but I rarely answer with a sed script. No context or explanation is necessary for trivial scripts that are explained by a glance at a man page.

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