shell script find and replace in file

Question

I have a file postmaster.log, in which I need to find pattern and change its value Pattern I need to find is

MaxValue=3 #this could be any value not just 3

I need to change its value to

MaxValue=0

Issue is there are also patterns like

"MaxValueSet=3" and "MaxValue is currently low"

Which are also getting replaced.I only has to change MaxValue=3 to MaxValue=0 I tried using sed

 sed -i 's/MaxValue=3/MaxValue=0/g' /home/postmaster.log

But this only works if MaxValue=3 for anyother value it won't work.

Jean-Baptiste Yunès · Accepted Answer · 2013-03-20 20:22:11Z

4

use a regexp to catch MaxValue= followed by any number...

s/MaxValue=[0-9]+/MaxValue=0/g

should work.

answered Mar 20, 2013 at 20:22

Jean-Baptiste Yunès

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5 Comments

JumpOffBox Over a year ago

I tried and it replaces whole line, I just want to replace MaxValue=3 with MaxValue=0, not the whole line. This works for whole line replacement though

ruakh Over a year ago

@JumpOffBox: Are you sure about that? This should only replace MaxValue= plus one or more digits. Can you give an example where it seems to replace more than that?

JumpOffBox Over a year ago

I am sure. I tried and its not working. Example of line from file VerifyValue=0 ; VerifyValue should be set to 0 MaxValue=5 ; Maximum number of Value for kernel jobs

JumpOffBox Over a year ago

if I use sed -i "s/MaxValue=.*/MaxValue=0/g", it works but it will replace the whole line not just MaxValue. Are there any other way aprt from sed

JumpOffBox Over a year ago

sed -i -r 's/MaxValue=[0-9]+/MaxValue=0/g' /home/postmaster.log

ruakh · Accepted Answer · 2013-03-20 20:22:14Z

2

It sounds like you want

sed -i 's/^MaxValue=.*/MaxValue=0/' /home/postmaster.log

which will find all lines that begin with MaxValue=, and replace each of those lines with MaxValue=0.

answered Mar 20, 2013 at 20:22

ruakh

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4 Comments

jahroy Over a year ago

As long as the OP wants to replace the entire line.

ruakh Over a year ago

@jahroy: Yes, absolutely. That's why I always make a point of explaining what the code does, so the OP can judge whether that's actually what (s)he wants.

JumpOffBox Over a year ago

I tried and it replaces whole line, I just want to replace MaxValue=3 with MaxValue=0, not the whole line. This works for whole line replacement though

ruakh Over a year ago

@JumpOffBox: Then Jean-Baptiste Yunès' answer is what you want.

chepner · Accepted Answer · 2013-03-20 21:33:45Z

1

You can restrict the lines sed works on as well:

sed -i '/^MaxValue=/s/=[[:digit:]][[:digit:]]*/=0/' /home/postmaster.log

edited Mar 20, 2013 at 21:33

answered Mar 20, 2013 at 20:30

chepner

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2 Comments

JumpOffBox Over a year ago

I tried and it replaces whole line, I just want to replace MaxValue=3 with MaxValue=0, not the whole line. This works for whole line replacement though

chepner Over a year ago

I've updated to only replace a positive integer value on the RHS. Other regular expressions can be given to more closely match your usage if necessary.

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