Sed, how to replace a string with a variable and string combination?

Question

The codeline below adds two different fixed-strings to beginning, and end of a line.

sed -i 's/.*/somefixedtext,&,someotherfixedtext/' ${f}

somefixedtext,20,30,10,50,someotherfixedtext

I want to enhance the output by using a variable, to give me below, instead of whats above;

HELLO,somefixedtext,20,30,10,50,someotherfixedtext

Tried some variations but all failed;

VARIABLE="HELLO"
sed -i 's/.*/"$VARIABLE,somefixedtext,&,someotherfixedtext/' ${f}

How can I incorporate a string variable to beginning of the line, combined with a fixedstring, in Sed ?

user000001 · Accepted Answer · 2017-02-11 17:31:19Z

4

Sed is a poor choice if the replacement string is from a variable, because it treats the variable as a sed command and not as literal string, so it will break if the variable contains special characters like / or & or similar.

Awk is better suited for this task, for example like:

$ cat file
20,30,10,50

$ var=hello

$ awk -F, -v prefix="$var" -v OFS=, '{print prefix, "sometext", $0, "somethingelse"}' file
hello,sometext,20,30,10,50,somethingelse

For inplace modification you will need a recent version of GNU awk, and the -i inplace arguments.

For what it's worth, the command would appear to work if you double quoted the variable, outside the single quotes, but it would be a bit buggy:

VARIABLE="HELLO"
sed -i 's/.*/'"$VARIABLE"',somefixedtext,&,someotherfixedtext/' ${f}

edited Feb 11, 2017 at 17:31

answered Feb 11, 2017 at 17:23

user000001

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1 Comment

Alp Alt Over a year ago

Thank you very much, the Sed version works very well. These two single quotes ate my 2 hours :)

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