Take the last word from a line and add it at the beginning using BASH - linux

Question

we have a requirement where contents of our text files are like this:
[some-section-1]
big_msg_line1 var=random_value1
big_msg_line2 var=random_value2
big_msg_line3 var=random_value3
[some-section-2]
"lots of irrelevant data"
[some-section-3]
"lots of irrelevant data"
[some-section-4]
big_msg_line4 var=random_value4
big_msg_line5 var=random_value5
big_msg_line6 var=random_value6
big_msg_line7 var=random_value7
big_msg_line8 var=random_value8
[some-section-5]
"lots of irrelevant data"
All the lines that we want to modify starts with common charaters, like in this example all lines which we would like to modify starts with the word "big". We would like to change it to something like this:
[some-section-1]
random_value1 msg=big_msg_line1
random_value2 msg=big_msg_line2
random_value3 msg=big_msg_line3
[some-section-2]
"lots of irrelevant data"
[some-section-3]
"lots of irrelevant data"
[some-section-4]
random_value4 msg=big_msg_line4
random_value5 msg=big_msg_line5
random_value6 msg=big_msg_line6
random_value7 msg=big_msg_line7
random_value8 msg=big_msg_line8
[some-section-5]
"lots of irrelevant data"
These were for examples only. The original file contains way lot more data than these. In hundreds if not in thousands lines.
I am currently doing this using for a loop, reading each line, cutting the values, formatting them like the way I want, putting then in separate file and then replace the original file with the new file. Is there a way to achieve this using some one liners? That would really be of great help. Hope I am clear with my question.
Thanks in advance.

Answer 1

From what I understood, this awk one-liner would do the job :
cat a
[some-section-1]
big_msg_line1 var=random_value1
big_msg_line2 var=random_value2
big_msg_line3 var=random_value3
[some-section-2]
lots of irrelevant data
[some-section-3]
lots of irrelevant data
[some-section-4]
big_msg_line4 var=random_value4
big_msg_line5 var=random_value5
big_msg_line6 var=random_value6
big_msg_line7 var=random_value7
big_msg_line8 var=random_value8
[some-section-5]
lots of irrelevant data
This :
awk '{FS="var="; if ($1~/big/) { print $2"\tmsg="$1} else {print }}' a
Gives
[some-section-1]
random_value1 msg=big_msg_line1
random_value2 msg=big_msg_line2
random_value3 msg=big_msg_line3
[some-section-2]
lots of irrelevant data
[some-section-3]
lots of irrelevant data
[some-section-4]
random_value4 msg=big_msg_line4
random_value5 msg=big_msg_line5
random_value6 msg=big_msg_line6
random_value7 msg=big_msg_line7
random_value8 msg=big_msg_line8
[some-section-5]
lots of irrelevant data

Answer 2

this command should do the job
sed -e 's/\(big[^ ]*\)\([ ]*\)var=\([^ ]*\)/\3\2msg=\1/' [your file] > [output file]
EDIT: You might need to change the slahes (/) to a letter which is not used in your file