使用awk修改文本

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.

Answer 2

It looks like you are using tabs instead of spaces as delimiters in your file, so:

awk 'BEGIN{FS="[=\t]"; OFS="\t"} {print $2, $3, $4}' input_file

or

awk 'BEGIN{FS="[=\t]"; OFS="\t"} {$1=""; gsub("\t\t", "\t"); print}' input_file

Answer 3

If you don't need to use awk , you can use sed , which I find a bit simpler. Hopefully you are familiar with regex operators, like ^ and . .

$ cat awkens
range=chr1      20802865        20802871
range=chr1      23866528        23866534
$ sed 's/^range=//' awkens
chr1      20802865        20802871
chr1      23866528        23866534