How to move a line from a file to the other file on the basis of pattern matching?

Question

I want to move lines from a text file into another text file. Those lines contain a word beginning with an underscore. This word is located on the sixth field of the lines; fields are separated with forward slashes. For example, move lines containing _Nokia on the sixth field, in the sample input file, below.

Apple/One-plus/Samsung/Mi/Sony/_Nokia/
Apple/One-plus/Samsung/Mi/Lenovo/_Nokia/
Apple/One-plus/Samsung/Mi/HTC/OPPO/

I have tried to move corresponding lines, with a regular expression, using grep, but it does not work.

$ grep -F 'Apple/One-plus/Samsung/Mi/^[a-zA-Z]([\w -]*[a-zA-Z])?$/_Nokia/' match.txt >file1.txt
$ grep -F -v "Apple/One-plus/Samsung/Mi/^[a-zA-Z]([\w -]*[a-zA-Z])?$/_Nokia/" match.txt \
    > match.txt.tmp && mv match.txt.tmp match

Expected output

$ cat file1.txt
Apple/One-plus/Samsung/Mi/Sony/_Nokia/
Apple/One-plus/Samsung/Mi/Lenovo/_Nokia/
$ cat match
Apple/One-plus/Samsung/Mi/HTC/OPPO/

How to move a line from a file to the other file on the basis of pattern matching?

Answer 1

Original issue

A regular expression cannot be specified with the -F option concerning grep. There is another issue concerning the regular expression. If the character ^ is used as an anchor to match the beginning of a line, then, it must be the first character of the regular expression.

prompt% cp -v input input.back
prompt% grep -e "$regex" input.back > output
prompt% grep -v "$regex" input.back > input

Regular expression: the original poster did not provide a concrete input, therefore, it is difficult to find a suitable regular expression.

Edit: finally, the original poster has provided a sample input file.

Apple/One-plus/Samsung/Mi/Sony/_Nokia/
Apple/One-plus/Samsung/Mi/Lenovo/_Nokia/
Apple/One-plus/Samsung/Mi/HTC/OPPO/

Regular expression: regex

regex='\([-[:alpha:]]\+\/\)\{5\}_Nokia\/'

Alternative solutions

These similar solutions are not recommended for beginners whom have never read the sed manual.

sed -n "/$regex/p;/$regex/d;w input" input.back > output

Roughly speaking, the lines matching the regular expression are saved in the file output, then, they are deleted from the corresponding sed buffer and the buffer content is written in the file input.

sed -i.back -e "/$regex/w output" -e "/$regex/d" input

These commands have subtle differences but the second one is more convenient.

Answer 2

If you have a suitably recent version of GNU awk (gawk) you could do

awk -i inplace -F'/' '$7 == "_f" {print > "otherfile"; next} 1' file

If your awk doesn't support the -i inplace option, then you can do the same thing but redirect the output to a temporary file and then rename it.

Answer 3

How about this proposition? This is a less concise proposition than @steeldriver's answer, nonetheless, it is a progressive solution (step by step).

$ cut -d/ -f7 data.txt  | grep -n _f | cut -d: -f 1 | xargs -i sed -n {}p data.txt > otherfile.txt

• _f is the pattern when matched is created to the other file.

• data.txt is your file

• / is your delimiter

If this worked, then do a comm to work out what should remain in the original file.

$ comm -23 data.txt otherfile.txt > remainder.txt

remainder.txt is your data.txt with the bits removed.

Answer 4

You can first move the intended lines to the other file (outemp.txt) by:

sed -n  '/_/w outemp.txt' input_file

then remove those lines from your input_file by:

sed  -i '/_/d' input_file

check the result:

cat outemp.txt 
Apple/One-plus/Samsung/Mi/Sony/_Nokia/
Apple/One-plus/Samsung/Mi/Lenovo/_Nokia/

cat input_file
Apple/One-plus/Samsung/Mi/HTC/OPPO/