Using a variable inside ’sed’

I have declared a variable in a file. I want to set the value of this variable, to a variable in a different file. When I tried to use ’sed’ to accomplish this, I encountered an error. The error was, its not getting the value from the old file and just places the variable name in the new file. By changing the command slightly, It works fine. Given below are the commands I used.

OLD-FILE

a=one

NEW-FILE

b=four

$ source OLD-FILE

$ sed -i ’s/b=.*/b=\${a}/’ NEW-FILE    #Output : b=${a}  #Wrong

$ sed -i ’s/b=.*/b=’$a/ NEW-FILE         #Output : b=one    #Correct One

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Published in: on August 9, 2007 at 8:00 pm Comments (4)

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4 Comments Leave a comment.

  1. On December 15, 2007 at 11:22 pm Idetrorce Said:

    very interesting, but I don’t agree with you
    Idetrorce

    Reply
  2. On August 14, 2008 at 7:44 am Ravi Said:

    I faced this problem and google search got me here.. thanks da sombai :-)

    Reply
  3. On January 5, 2009 at 9:20 am star Said:

    this works:
    a=”hello”
    sed -e s/b=.*/b=”$a”/ OLDFILE

    do not using -e ’something’ ,while use “” to include the variable

    Reply
  4. On March 24, 2009 at 8:19 am Ray Brannam Said:

    This was exactly what I needed.

    MSG2=`echo ${MSG1} | sed ’s/$A/’${START}/g | sed ’s/$B/’${STOP}/g`
    echo “${MSG2}”

    Now prints exactly what I intended instead of variable names.

    Thanks!

    Reply

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