I have this file :
>AX-899-Af-889-[A/G]
GTCCATTCAGGTAAAAAAAAAAAACATAACAATTGAAATTGCATGA
>AX-899-Af-889-[A/G]
GCAAACTATTTTCATGAATGAACTTCAGTTGATTGTGAGATG
>AX-899-Af-889-[G/T]
AAGGTAGAATGACACCATTAAACAGTAGGGAATTGGTCACAGAACTCT
I need to insert the pattern [X/X] present in the lines starting by > in the next line at the 10th position and replace this 10th character :
>AX-899-Af-889-[A/G]
GTCCATTCA[A/G]GTAAAAAAAAAAAACATAACAATTGAAATTGCATGA
>AX-899-Af-889-[A/G]
GCAAACTAT[A/G]TTCATGAATGAACTTCAGTTGATTGTGAGATG
>AX-899-Af-889-[G/T]
AAGGTAGAA[G/T]GACACCATTAAACAGTAGGGAATTGGTCACAGAACTCT
I can extract the pattern :
awk 'match($0, /^>/) {split($0,a,"-"); print; getline; print a[5]}1' file
Also replace the 10th character by a pattern ("N" for example) : sed 's/^\([ATCG].\{8\}\)[ATCG]/\1N/' file