Query:

I tried to use a shell script to do a for loop: 

#!...bash 
for i in (5, 10, 15, 20) do; 
sed 's/bpp=64/bpp=$i/g' myfile.c > myfile2.c 
~~ 
done 

However, each time it executes, "bpp=64" becomes "bpp=$i" instead of 
"bpp=5" ...... 

How to make the $i inside sed command to be a real variable. 

Solution:

For variables double quote, for wyswyg characters single quote. Concatenate when both are present:

Code:

#if there were regular ocurrences of $ you could concatenate:

sed  's/bpp=64/bpp='"$i/g"  myfile.c  >  myfile2.c 
 

#if you only use $ for variables, just double quote:

sed  "s/bpp=64/bpp=$i/g"  myfile.c  >  myfile2.c
 

Query:

I want to use variables in a script using a sed command line. How can I do?

Imagine there's a file containing on each line a number ("2" on the first line of the file "file1"). I want to stock the number on a given line. For example I want the number of the first line. I'd like to to something like that : sed -n '1,1p' file1 but with variables, like that :

In this case, i would be equal to 1
var1=$i,$i
var2="$var1"p
sed -n 'var2' file1

How can I do that ?

Solution:

sed s/$var1/$var2/ file

this goes to stndout, so just redirect to a new file if necessary

sed s/$var1/$var2/ file > newfile
 

Query:

I would like to use 'sed' to edit a file by searching for a fixed string and replacing it with an environment variable that is dynamically set with, in this case, the current date and time.

I'm trying this format of the command:

sed 's/XXXXXX/${env_var}/' filein.txt

The command replaces the 'XXXXXX' with literally '${env_var}' and not the interpretation of the variable. I have set the variable before trying to run this command.

It appears 'sed' will only replace using literally what's between the delimiter characters.

Any way to do this?

Solution:

Change your single quotes to double quotes in your sed command. 

Double quotes allow shell expansion; single quotes protect from shell expansion.

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