Find a pattern and replace - linux

Question

This is the input to my file.
Number : 123
PID : IIT/123/Dakota
The expected output is :
Number : 111
PID : IIT/111/Dakota
I want to replace 123 to 111. To solve this I have tried following:
awk '/Number/{$NF=111} 1' log.txt
awk -F '[/]' '/PID/{$2="123"} 1' log.txt

Answer 1

Use sed for something this simple ?
Print the change to the screen (test with this) :
sed -e 's:123:111:g' f2.txt
Update the file (with this) :
sed -i 's:123:111:g' f2.txt
Example:
$ sed -i 's:123:111:g' f2.txt
$ cat f2.txt
Number : 111
PID : IIT/111/Dakota

Answer 2

EDIT2: Or you want to substitute each line's 123 with 111 without checking any condition which you tried in your awk then simply do:
awk '{sub(/123/,"111")} 1' Input_file
Change sub to gsub in case of many occurrences of 123 in a single line too.
Explanation of above code:
awk -v new_value="111" ' ##Creating an awk variable named new_value where OP could keep its new value which OP needs to be there in line.
/^Number/ { $NF=new_value } ##Checking if a line starts from Number string and then setting last field value to new_value variable here.
/^PID/ { num=split($NF,array,"/"); ##Checking if a line starts from PID then creating an array named array whose delimiter it / from last field value
array[2]=new_value; ##Setting second item of array to variable new_value here.
for(i=1;i<=num;i++){ val=val?val "/" array[i]:array[i] }; ##Starting a loop from 1 to till length of array and creating variable val to re-create last field of current line.
$NF=val; ##Setting last field value to variable val here.
val="" ##Nullifying variable val here.
}
1' Input_file ##Mentioning 1 to print the line and mentioning Input_file name here too.
EDIT: In case you need to / in your output too then use following awk.
awk -v new_value="111" '
/^Number/ { $NF=new_value }
/^PID/ { num=split($NF,array,"/");
array[2]=new_value;
for(i=1;i<=num;i++){ val=val?val "/" array[i]:array[i] };
$NF=val;
val=""
}
1' Input_file
Following awk may help you here.(Seems after I have applied code tags to your samples your sample input is changed a bit so editing my code accordingly now)
awk -F"[ /]" -v new_value="111" '/^Number/{$NF=new_value} /^PID/{$(NF-1)=new_value}1' Input_file
In case you want to save changes into Input_file itself append > temp_file &7 mv temp_file Input_file in above code then.
Explanation:
awk -F"[ /]" -v new_value="111" ' ##Setting field separator as space and / to each line and creating awk variable new_value which OP wants to have new value.
/^Number/{ $NF=new_value } ##Checking condition if a line is starting with string Number then change its last field to new_value value.
/^PID/ { $(NF-1)=new_value } ##Checking condition if a line starts from string PID then setting second last field to variable new_value.
1 ##awk works on method of condition then action, so putting 1 making condition TRUE here and not mentioning any action so by default print of current line will happen.
' Input_file ##Mentioning Input_file name here.