sed not capturing regex

Question

I'm attempting to replace the beginning of lines in a simple file.

>1
TGAACCATCGAGTCTTTGAACG
>2
GAGTTCATTTCTCTCTGGAGGCACC
>3
ATTGACAGATTGAGAGCTCTTTC
>4
CGGGAAAAGGATTGGCTC
>5
TCTTGGTGGTAGTAGCAAATATTCAAATG

Above is the input, below is the desired output.

>seq_x1
TGAACCATCGAGTCTTTGAACG
>seq_x2
GAGTTCATTTCTCTCTGGAGGCACC
>seq_x3
ATTGACAGATTGAGAGCTCTTTC
>seq_x4
CGGGAAAAGGATTGGCTC
>seq_x5
TCTTGGTGGTAGTAGCAAATATTCAAATG

Here is the command I've tried using:

sed -n -r 's/^>(\d+)/>seq_x\1/' file

Using text editors on a small subset of the file, I have no problem with find and replace using '^>(\d+)' and '>seq_x\1', but I can't get sed to replace effectively. Is there something I'm missing?

Gotcha. That works. I didn't know \d wasn't matching digits in sed. For those viewing later, the linked [duplicate] explains more. — underasail, Mar 26 '18 at 13:35

score 1 · Accepted Answer · answered Mar 26 '18 at 13:22

1

In your simple case there's no need to specify a followed digit.
Besides, you should use a more portable [0-9] (range of numbers) instead of \d+.

sed 's/^>/>seq_x/' file

answered Mar 26 '18 at 13:22

RomanPerekhrest

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sed not capturing regex

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