Question

I am trying to modify text files using awk. There are three columns and I want to delete part of the text in the first column:

range=chr1      20802865        20802871        
range=chr1      23866528        23866534

to

chr1      20802865        20802871        
chr1      23866528        23866534

How can I do this?

I’ve tried awk '{ substr("range=chr*", 7) }' and awk '{sub(/[^[:space:]]*\\/, "")}1' but it deletes all the contents of the file.

Answer 1

Set the field separator as = and print the second field:

# With awk                                                                     
$ awk -F= '{print $2}' file
chr1      20802865        20802871        
chr1      23866528        23866534

# Or with cut
$ cut -d= -f2 file                  
chr1      20802865        20802871        
chr1      23866528        23866534

# How about grep
$ grep -Po '(?<==).*' file
chr1      20802865        20802871        
chr1      23866528        23866534

# Temp file needed
$ cut -d= -f2 file > tmp; mv tmp file

Both awk, cut and grep require temporary files if you want to store the changes back into file, a better solution would be to use sed:

 sed -i 's/range=//' file

This substitutes range= with nothing and the -i means the changes are done in-place so no need to handle the temporary files stuff as sed does it for you.