Generally, FASTA files contain multiple sequence lines (wrapped at n? chars), per header line, which means your example could be misleading. If that is the case, then something like this may be needed: 

#! perl -slw
use strict;

my( $x, $y ) = ( 3, 5 );

while( <DATA> ) {
    chomp;
    print ">$_";
    local $/ = '>';
    $_ = <DATA>;
    chomp;
    tr[\n][]d;
    print for unpack '(A36)*', substr $_, $x, length() - $x - $y;
}

__DATA__
>HWI-EAS158_40_3_1_46_535
GTGAATGCGTGATACAGGAATGTTCGTTGTGACCAT
>HWI-EAS158_40_3_1_47_579
AAAGTGAATGCGTGATACAGGAATGTTCGTTGTGAC
AAAGTGAATGCGTGATACAGGAATGTTCGTTGTGAC
AAAGTGAATGCGTGATACAGGAATGTTCGTTGTGAC
AAAGTGAATGCGTGATACAGGAATGTTCGTTGTGAC
>HWI-EAS158_40_3_1_46_731
GTGTCATGCGTGATACAGGAATGTTCGTTGTGAAAA
GTGTCATGCGTGATACAGGAATGTTCGTTGTGAAAA
GTGTCATGCGTGATACAGGAATGTTCGTTGTGAAAA

[download]

Produces:

c:\test>junk46
>>HWI-EAS158_40_3_1_46_535
AATGCGTGATACAGGAATGTTCGTTGTG
>HWI-EAS158_40_3_1_47_579
GTGAATGCGTGATACAGGAATGTTCGTTGTGACAAA
GTGAATGCGTGATACAGGAATGTTCGTTGTGACAAA
GTGAATGCGTGATACAGGAATGTTCGTTGTGACAAA
GTGAATGCGTGATACAGGAATGTTCGTT
>HWI-EAS158_40_3_1_46_731
TCATGCGTGATACAGGAATGTTCGTTGTGAAAAGTG
TCATGCGTGATACAGGAATGTTCGTTGTGAAAAGTG
TCATGCGTGATACAGGAATGTTCGTTGT

[download]
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"I'd rather go naked than blow up my ass"

In reply to Re: simple perl script to trim a FASTA file by BrowserUk
in thread simple perl script to trim a FASTA file by RabidMortal

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.