there are 200 files named File1_0.pdb,File1_60.pdb etc....it looks like:
ATOM 1 N VAL 1 8.897 -21.545 -7.276 1.00 0.00
ATOM 2 H1 VAL 1 9.692 -22.015 -6.868 1.00 0.00
ATOM 3 H2 VAL 1 9.228 -20.766 -7.827 1.00 0.00
ATOM 4 H3 VAL 1 8.289 -22.236 -7.693 1.00 0.00
TER
ATOM 5 CA VAL 1 8.124 -20.953 -6.203 1.00 0.00
ATOM 6 HA VAL 1 8.072 -19.874 -6.345 1.00 0.00
ATOM 7 CB VAL 1 6.693 -21.515 -6.176 1.00 0.00
ATOM 8 HB VAL 1 6.522 -22.024 -5.227 1.00 0.00
ATOM 9 CG1 VAL 1 5.684 -20.370 -6.330 1.00 0.00
ATOM 10 1HG1 VAL 1 5.854 -19.861 -7.279 1.00 0.00
i have to extract the part after TER and put in a different file...this has to be done on all 200 files. I did something like sed '1,/TER/d' File1_0.pdb > 1_0.pdb. But this will work for one file at a time...can there be a solution for all 200 files in one go... output file is named same only "File" is removed from the name...
for i in *.pdb; do sed '1,/TER/d' $i > ${i/File/}; done
This might work:
seq 0 200| xargs -i -n1 cp File1_{}.pdb 1_{}.pbd # backup files
sed -si '1,/TER/d' 1_{0..200}.pdb # edit files separately inline
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I'm trying to find a way to write a script that does the following:
Open and detect the first use of a three-letter sequence that is repeated in the input file
Edit and permute this three letter sequence 19 times, giving 19 outputs each with a different three letter code that corresponds to a list of 19 possible three letter codes
Essentially, this is a fairly straightforward find and replace problem that I know how to do. The problem is that I then need to loop this so that, after creating the 19 files from the previous line, the next line with a different three letter code has the same replacement done to it.
I'm struggling to find a way to have the script recognize sequences of text when it can be one of twenty different things.
Let me know if anyone has any ideas on how I could go about doing this, I'll provide any clarification if necessary too!
Here is an example of an input file:
ATOM 1 N SER A 2 37.396 -5.247 -4.830 1.00 65.06 N
ATOM 2 CA SER A 2 37.881 -6.354 -3.929 1.00 64.88 C
ATOM 3 C SER A 2 36.918 -7.555 -3.786 1.00 64.14 C
ATOM 4 O SER A 2 37.287 -8.576 -3.177 1.00 64.31 O
ATOM 5 CB SER A 2 38.251 -5.804 -2.552 1.00 65.31 C
ATOM 6 OG SER A 2 37.122 -5.210 -1.918 1.00 66.94 O
ATOM 7 N GLU A 3 35.705 -7.438 -4.342 1.00 62.82 N
ATOM 8 CA GLU A 3 34.716 -8.539 -4.306 1.00 61.94 C
ATOM 9 C GLU A 3 35.126 -9.833 -5.033 1.00 59.71 C
ATOM 10 O GLU A 3 34.927 -10.911 -4.473 1.00 59.23 O
ATOM 11 CB GLU A 3 33.328 -8.094 -4.789 1.00 62.49 C
ATOM 12 CG GLU A 3 32.291 -7.994 -3.693 1.00 66.67 C
ATOM 13 CD GLU A 3 31.552 -9.302 -3.426 1.00 71.93 C
ATOM 14 OE1 GLU A 3 32.177 -10.254 -2.892 1.00 73.96 O
ATOM 15 OE2 GLU A 3 30.329 -9.364 -3.723 1.00 74.25 O
ATOM 16 N PRO A 4 35.663 -9.732 -6.280 1.00 57.83 N
ATOM 17 CA PRO A 4 36.131 -10.951 -6.967 1.00 56.64 C
Where an output would look like this:
ATOM 1 N ALA A 2 37.396 -5.247 -4.830 1.00 65.06 N
ATOM 2 CA SER A 2 37.881 -6.354 -3.929 1.00 64.88 C
ATOM 3 C SER A 2 36.918 -7.555 -3.786 1.00 64.14 C
ATOM 4 O SER A 2 37.287 -8.576 -3.177 1.00 64.31 O
ATOM 5 CB SER A 2 38.251 -5.804 -2.552 1.00 65.31 C
ATOM 6 OG SER A 2 37.122 -5.210 -1.918 1.00 66.94 O
ATOM 7 N GLU A 3 35.705 -7.438 -4.342 1.00 62.82 N
ATOM 8 CA GLU A 3 34.716 -8.539 -4.306 1.00 61.94 C
ATOM 9 C GLU A 3 35.126 -9.833 -5.033 1.00 59.71 C
ATOM 10 O GLU A 3 34.927 -10.911 -4.473 1.00 59.23 O
ATOM 11 CB GLU A 3 33.328 -8.094 -4.789 1.00 62.49 C
ATOM 12 CG GLU A 3 32.291 -7.994 -3.693 1.00 66.67 C
ATOM 13 CD GLU A 3 31.552 -9.302 -3.426 1.00 71.93 C
ATOM 14 OE1 GLU A 3 32.177 -10.254 -2.892 1.00 73.96 O
ATOM 15 OE2 GLU A 3 30.329 -9.364 -3.723 1.00 74.25 O
ATOM 16 N PRO A 4 35.663 -9.732 -6.280 1.00 57.83 N
ATOM 17 CA PRO A 4 36.131 -10.951 -6.967 1.00 56.64 C
On the first pass, the SER should be changed to a series of twenty different text sequences, the first being ALA. The issue I'm having is that I'm not sure how to write a script that will change more than one line of text.
My current script can form the 19 mutations of the first SER, but that's where it will stop. It won't mutate the next one, and it won't mutate a different three letter code, for example it wouldn't change the GLU. Is there any easy way to integrate this functionality?
Currently, the way I've approached this is to do a simple text transformation using sed, but as this seems more complicated than what sed can bring to the table, I think perl is likely the way to go. I can add the sed code, but I didn't think it would be of much help.
Your question and comments aren't entirely clear, but I believe this script will do what you want. It parses a PDB file until it reaches the amino acid of interest. A set of 19 files are produced where this AA is substituted by the other 19 AAs. From there onwards, every time an AA differs from the AA in the previous line, another set of 19 files will be generated.
#!/usr/bin/perl
use warnings;
use strict;
# we're going to start mutating when we find this residue.
my $target = 'GLU';
my #aas = ( 'ALA', 'ARG', 'ASN', 'ASP', 'CYS', 'GLU', 'GLN', 'GLY', 'HIS', 'ILE', 'LEU', 'LYS', 'MET', 'PHE', 'PRO', 'SER', 'THR', 'TRP', 'TYR', 'VAL' );
my $prev = '';
my $line_no = 0;
my #lines;
my %changes;
# uncomment the following lines and comment out "while (<DATA>) {"
# to read the input from a file
# my $input = 'path/to/pdb_file';
# open( my $fh, "<", $input ) or die "Could not open $input: $!";
# while (<$fh>) {
while (<DATA>) {
# split the line into columns (assuming it is tab-delimited;
# switch this for "\s+" if it is separated with whitespace.
my #cols = split "\t";
if ($target && $cols[3] eq $target) {
# Found our target residue! unset $target so that the following
# set of tests are performed
undef $target;
}
# see if this AA is the same as the AA in the previous line
if (! $target && $prev ne $cols[3]) {
# if it isn't, store the line number and the amino acid
$changes{ $line_no } = $cols[3];
# update $prev to reflect the new AA
$prev = $cols[3];
}
# store all the lines
push #lines, $_;
# increment the line number
$line_no++;
}
# now, for each of the changes, create substitute files
for (keys %changes) {
create_substitutes($_, $changes{$_}, [#aas], [#lines]);
}
sub create_substitutes {
# arguments: line no, $res: residue, $aas: array of amino acids,
# $all_lines: all lines in the file
my ($line_no, $res, $aas, $all_lines) = #_;
# this is the target line that we want to substitute
my #target = split "\t", $all_lines->[$line_no];
# for each AA in the list of AAs, create a new file called 'XXX-##.txt',
# where XXX is the amino acid and ## is the line number where the
# substituted residue is.
for (#$aas) {
next if $_ eq $res;
open( my $fh, ">", $_."-$line_no.txt") or die "Could not create output file for $_: $!";
# print out all lines up to the changed line
print { $fh } #$all_lines[0..$line_no-1];
# print out the changed line, substituting in the AA
print { $fh } join "\t", #target[0..2], $_, #target[4..$#target];
# print out the rest of the lines.
print { $fh } #$all_lines[$line_no+1 .. $#{$all_lines}];
}
}
__DATA__
ATOM 1 N SER A 2 37.396 -5.247 -4.830 1.00 65.06 N
ATOM 2 CA SER A 2 37.881 -6.354 -3.929 1.00 64.88 C
ATOM 3 C SER A 2 36.918 -7.555 -3.786 1.00 64.14 C
ATOM 4 O SER A 2 37.287 -8.576 -3.177 1.00 64.31 O
ATOM 5 CB SER A 2 38.251 -5.804 -2.552 1.00 65.31 C
ATOM 6 OG SER A 2 37.122 -5.210 -1.918 1.00 66.94 O
ATOM 7 N GLU A 3 35.705 -7.438 -4.342 1.00 62.82 N
ATOM 8 CA GLU A 3 34.716 -8.539 -4.306 1.00 61.94 C
ATOM 9 C GLU A 3 35.126 -9.833 -5.033 1.00 59.71 C
ATOM 10 O GLU A 3 34.927 -10.911 -4.473 1.00 59.23 O
ATOM 11 CB GLU A 3 33.328 -8.094 -4.789 1.00 62.49 C
ATOM 12 CG GLU A 3 32.291 -7.994 -3.693 1.00 66.67 C
ATOM 13 CD GLU A 3 31.552 -9.302 -3.426 1.00 71.93 C
ATOM 14 OE1 GLU A 3 32.177 -10.254 -2.892 1.00 73.96 O
ATOM 15 OE2 GLU A 3 30.329 -9.364 -3.723 1.00 74.25 O
ATOM 16 N PRO A 4 35.663 -9.732 -6.280 1.00 57.83 N
ATOM 17 CA PRO A 4 36.131 -10.951 -6.967 1.00 56.64 C
ATOM 18 CA ARG A 4 36.131 -10.951 -6.967 1.00 56.64 C
This example data will produce a set of files for the first GLU found (line 6), then another set for line 15 (PRO residue), and another set for line 17 (ARG residue).
Example of ALA-6.txt file:
ATOM 1 N SER A 2 37.396 -5.247 -4.830 1.00 65.06 N
ATOM 2 CA SER A 2 37.881 -6.354 -3.929 1.00 64.88 C
ATOM 3 C SER A 2 36.918 -7.555 -3.786 1.00 64.14 C
ATOM 4 O SER A 2 37.287 -8.576 -3.177 1.00 64.31 O
ATOM 5 CB SER A 2 38.251 -5.804 -2.552 1.00 65.31 C
ATOM 6 OG SER A 2 37.122 -5.210 -1.918 1.00 66.94 O
ATOM 7 N ALA A 3 35.705 -7.438 -4.342 1.00 62.82 N
ATOM 8 CA GLU A 3 34.716 -8.539 -4.306 1.00 61.94 C
ATOM 9 C GLU A 3 35.126 -9.833 -5.033 1.00 59.71 C
(etc.)
If this isn't the correct behaviour, you'll have to edit your question as it isn't very clear!
Because your question isn't very clear (more precisely, it is totally unclear), i created the following:
#!/usr/bin/env perl
use 5.014;
use strict;
use warnings;
use Path::Tiny;
use Bio::PDB::Structure;
use Data::Dumper;
my $residues_file = "input2.txt"; #residue names, one per line
my $molfile = "m1.pdb"; #molecule file
#read the residues
my(#residues) = path($residues_file)->lines({chomp => 1});
my $m= Bio::PDB::Structure::Molecule->new;
for my $res (#residues) { #for each residue name from a file "input2.txt"
$m->read("m1.pdb"); #read the molecule
my $atom = $m->atom(0); #get the 1st atom
$atom->residue_name($res); #change the residue to the from file
#create output filename
my $outfile = path($molfile)->basename('.pdb') . '_' . lc($res) . '.pdb';
#write the result
$m->print($outfile);
}
for example, if the input2.txt contains
ALA
ARG
ASN
ASP
CYS
GLN
GLU
GLY
HIS
ILE
LEU
LYS
MET
PHE
PRO
SER
THR
TRP
TYR
VAL
the from your input, generates 20 files where the residue in the 1st atom is changed (according to your output example) to like:
==> m1_ala.pdb <==
ATOM 1 N ALA A 2 37.396 -5.247 -4.830 1.00 65.06
==> m1_arg.pdb <==
ATOM 1 N ARG A 2 37.396 -5.247 -4.830 1.00 65.06
==> m1_asn.pdb <==
ATOM 1 N ASN A 2 37.396 -5.247 -4.830 1.00 65.06
==> m1_asp.pdb <==
ATOM 1 N ASP A 2 37.396 -5.247 -4.830 1.00 65.06
==> m1_cys.pdb <==
ATOM 1 N CYS A 2 37.396 -5.247 -4.830 1.00 65.06
... etc, 20 times...
I have a large file like below, I want to split this file into multiple files. Each file should be break after ENDMDL. For the following file there will be three output files with name pose1.av, pose2.av and pose3.av.
MODEL 1
SML 170 O PRO A 17 16.893 3.030 0.799 1.00 1.00 O
SML 171 OXT PRO A 17 18.167 2.722 2.597 1.00 1.00 O
TER 172 PRO A 17
ENDMDL
MODEL 2
SML 4 CG ARG A 1 -2.171 -7.105 -4.278 1.00 1.00 C
SML 5 CD ARG A 1 -1.851 -8.581 -4.022 1.00 1.00 C
SML 113 HD1 HIS A 12 2.465 -8.206 5.062 1.00 1.00 H
TER 114 HIS A 12
ENDMDL
MODEL 3
SML 101 N HIS A 12 3.765 -3.995 7.233 1.00 1.00 N
SML 102 CA HIS A 12 2.584 -4.736 6.934 1.00 1.00 C
TER 103 HIS A 12
ENDMDL
A rather efficient one, using bash and sed:
n=0
while IFS= read -r firstline; do
{ echo "$firstline"; sed '/^ENDMDL$/q'; } > "pose$((++n)).av"
done < file
It's much more efficient than the other Bash answer: the output file is only opened once, and most of the parsing is done by sed, and not by bash.
csplit can do this out of the box
csplit -z -s -f pose -b "%01d.av" file '/^ENDMDL$/+1' '{*}'
Awk is a good choice for this task:
awk '{file="pose"++i;printf "%s%s",$0,RS > file;close(file)}' RS='ENDMDL\n' file
Using a perl one-liner
perl -ne '$fh or open $fh, "> pose".++$i".av"; print $fh $_; undef $fh if /^ENDMDL/' file.txt
In pure Bash:
cnt=1
while read line; do
echo "$line" >> pose${cnt}.av
[ "$line" == "ENDMDL" ] && let cnt+=1
done < filename.txt
awk '/^MODEL/{out="pose"++cnt".av"} {print > out}' file
I have a tab separated text file called test.txt with multiple columns that I'm trying to make identical to another file called output.txt.
The test.txt looks as follows
t m sx sy sz rx ry rz
49.07 0 -1.00 0.00 -0.11 20.00 0.00 -2.18
49.47 0 -1.00 0.00 -0.11 22.00 0.00 -2.33
50.89 0 -1.00 0.00 -0.11 34.00 0.00 -3.21
.
:
42.06 0 29.00 0.00 -2.86 12.00 0.00 -1.44
The problem is that, no matter what type of delimiter I use, still it will not have the same form as the desired output file called output.txt
In the output.txt, all these columns have a specific location, so
t m sx sy sz rx ry rz
Ln1,col1 Ln1,col9 Ln1,col17 Ln1,col25 Ln1,col33 Ln1,col41 Ln1,col49 Ln1,col57
I'm a bit new with awk, sed and most of other unix commands. Any suggestion?
have you tried something like this?
awk -F 'BEGIN{print "t\tm\tsx\tsy\tsz\trx\try\trz"}{print $1"\t"$9"\t"$17"\t"$25"\t"$33"\t"$41"\t"$49}' test.txt
You print the header at the beginning and then for each line you print the desired columns
example for printf:
awk '{for (i=1;i<=NF;i++) printf(\"%-9s\", $i); print}' file
more examples
I have a text file (the first two lines are character spacings):
1 2 3 4 5 6 7 8
12345678901234567890123456789012345678901234567890123456789012345678901234567890
ATOM 1 N1 SPINA 3 30.616 29.799 14.979 1.00 20.00 S N
ATOM 2 N1 SPINA 3 28.146 28.381 13.950 1.00 20.00 S N
ATOM 3 N1 SPINA 3 27.605 28.239 14.037 1.00 20.00 S N
ATOM 4 N1 SPINA 3 30.333 29.182 15.464 1.00 20.00 S N
ATOM 5 N1 SPINA 3 29.608 29.434 14.333 1.00 20.00 S N
ATOM 6 N1 SPINA 3 29.303 29.830 13.317 1.00 20.00 S N
ATOM 7 N1 SPINA 3 28.963 31.116 13.472 1.00 20.00 S N
ATOM 8 N1 SPINA 3 28.859 28.743 13.828 1.00 20.00 S N
ATOM 9 N1 SPINA 3 29.699 30.575 14.564 1.00 20.00 S N
ATOM 10 N1 SPINA 3 29.518 29.194 15.301 1.00 20.00 S N
I want to edit it and make it like:
1 2 3 4 5 6 7 8
12345678901234567890123456789012345678901234567890123456789012345678901234567890
ATOM 1 N001 SPINA 3 30.616 29.799 14.979 1.00 20.00 S N
ATOM 2 N002 SPINA 3 28.146 28.381 13.950 1.00 20.00 S N
ATOM 3 N003 SPINA 3 27.605 28.239 14.037 1.00 20.00 S N
ATOM 4 N004 SPINA 3 30.333 29.182 15.464 1.00 20.00 S N
ATOM 5 N005 SPINA 3 29.608 29.434 14.333 1.00 20.00 S N
ATOM 6 N006 SPINA 3 29.303 29.830 13.317 1.00 20.00 S N
ATOM 7 N007 SPINA 3 28.963 31.116 13.472 1.00 20.00 S N
ATOM 8 N008 SPINA 3 28.859 28.743 13.828 1.00 20.00 S N
ATOM 9 N009 SPINA 3 29.699 30.575 14.564 1.00 20.00 S N
ATOM 10 N010 SPINA 3 29.518 29.194 15.301 1.00 20.00 S N
The number of spaces between each column are important and the list of atoms needs to go up to 190 (N001-N190). Thus I would like to replace characters 13-16 (" N1 ") in file 1 with ("N001") and keep the remainder of the file in the original spacing.
You don't need 10 long lines of sample input to demonstrate the problem or the solution:
$ cat file
ATOM 1 N1 SPINA 3
ATOM 2 N1 SPINA 3
ATOM 10 N1 SPINA 3
$ awk '{print substr($0,1,12) sprintf("N%03d",$2) substr($0,17)}' file
ATOM 1 N001 SPINA 3
ATOM 2 N002 SPINA 3
ATOM 10 N010 SPINA 3
I'm assuming we could use $2 as the numeric part of the 3rd field. It seems to increment sequentially with your line numbers. Using NR might be an alternative. If neither of those is actually what you want, post some more representative sample input/output.
Also, note that any solution that involves assigning to a field (e.g. $3=...) WILL cause awk to recompile the line using the value of OFS as the field separator and so will change your spacing.
Oh, and if those 2 initial lines of character spacings are really present in your files, this is the tweak:
$ cat file
1 2
12345678901234567890123456
ATOM 1 N1 SPINA 3
ATOM 2 N1 SPINA 3
ATOM 10 N1 SPINA 3
$ awk 'NR>2{$0 = substr($0,1,12) sprintf("N%03d",$2) substr($0,17)} 1' file
1 2
12345678901234567890123456
ATOM 1 N001 SPINA 3
ATOM 2 N002 SPINA 3
ATOM 10 N010 SPINA 3
Try :
$ awk '{$3=substr($3,1,1) sprintf("%03d",$2)}1' OFS=\\t file
Note : OFS will be tab
If you want to try this on a Solaris/SunOS system, change awk to /usr/xpg4/bin/awk , /usr/xpg6/bin/awk , or nawk
--edit--
if you want to increment with line
$ awk '{$3=substr($3,1,1) sprintf("%03d",NR)}1' OFS=\\t file
Here is yet another way:
awk 'sub(/.$/,sprintf("%03d",NR),$3)' OFS='\t' file
Output:
$ awk 'sub(/.$/,sprintf("%03d",NR),$3)' OFS='\t' file
ATOM 1 N001 SPINA 3 30.616 29.799 14.979 1.00 20.00 S N
ATOM 2 N002 SPINA 3 28.146 28.381 13.950 1.00 20.00 S N
ATOM 3 N003 SPINA 3 27.605 28.239 14.037 1.00 20.00 S N
ATOM 4 N004 SPINA 3 30.333 29.182 15.464 1.00 20.00 S N
ATOM 5 N005 SPINA 3 29.608 29.434 14.333 1.00 20.00 S N
ATOM 6 N006 SPINA 3 29.303 29.830 13.317 1.00 20.00 S N
ATOM 7 N007 SPINA 3 28.963 31.116 13.472 1.00 20.00 S N
ATOM 8 N008 SPINA 3 28.859 28.743 13.828 1.00 20.00 S N
ATOM 9 N009 SPINA 3 29.699 30.575 14.564 1.00 20.00 S N
ATOM 10 N010 SPINA 3 29.518 29.194 15.301 1.00 20.00 S N
If you are interesting to resolve it with pure shell, here is the code:
while IFS="\n" read -r line
do
n=${line:9:3}
printf "%sN%03d%s\n" "${line:0:12}" $n "${line:16}"
done < file
awk '$3="N"sprintf("%03d",$2)' OFS='\t' infile.txt
Result
ATOM 1 N001 SPINA 3 30.616 29.799 14.979 1.00 20.00SN
ATOM 2 N002 SPINA 3 28.146 28.381 13.950 1.00 20.00SN
ATOM 3 N003 SPINA 3 27.605 28.239 14.037 1.00 20.00SN
ATOM 4 N004 SPINA 3 30.333 29.182 15.464 1.00 20.00SN
ATOM 5 N005 SPINA 3 29.608 29.434 14.333 1.00 20.00SN
ATOM 6 N006 SPINA 3 29.303 29.830 13.317 1.00 20.00SN
ATOM 7 N007 SPINA 3 28.963 31.116 13.472 1.00 20.00SN
ATOM 8 N008 SPINA 3 28.859 28.743 13.828 1.00 20.00SN
ATOM 9 N009 SPINA 3 29.699 30.575 14.564 1.00 20.00SN
ATOM 10 N010 SPINA 3 29.518 29.194 15.301 1.00 20.00SN
I have pdb (protein data base) file which has thousands of lines.
REMARK 1 PDB file generated by ptraj (set 1000)
ATOM 1 O22 DDM 1 2.800 4.419 20.868 0.00 0.00
ATOM 2 H22 DDM 1 3.427 4.096 20.216 0.00 0.00
ATOM 3 C22 DDM 1 3.351 5.588 21.698 0.00 0.00
ATOM 4 H42 DDM 1 3.456 5.274 22.736 0.00 0.00
ATOM 5 C23 DDM 1 2.530 6.846 21.639 0.00 0.00
ATOM 6 H43 DDM 1 2.347 7.159 20.611 0.00 0.00
ATOM 7 O23 DDM 1 1.313 6.498 22.334 0.00 0.00
ATOM 8 H23 DDM 1 0.903 5.837 21.771 0.00 0.00
ATOM 9 C24 DDM 1 3.073 8.109 22.266 0.00 0.00
ATOM 10 H44 DDM 1 3.139 7.837 23.319 0.00 0.00
ATOM 11 O24 DDM 1 2.218 9.278 22.007 0.00 0.00
ATOM 12 H24 DDM 1 1.278 9.184 22.179 0.00 0.00
ATOM 13 C25 DDM 1 4.494 8.317 21.764 0.00 0.00
ATOM 14 H45 DDM 1 4.391 8.452 20.687 0.00 0.00
'
I want to insert word "TER" every 81 lines in that file whcih contains more than 20,000 lines but ignoring the first line since it is a comment.
I browse through internet, seems SED can do it. But i am lost.
Can anyone guide?
Thanks in advance.
Try this:
sed -i -e '1~81 i\TER' file
I'm partial to awk myself:
awk '{if(FNR%81==0)print "TER"; print}' file
I find this is a lot easier to understand and debug than the sed equivalent. The only magic is that FNR is the line number
You might have to fiddle with the numbers in the if to get it exactly the way you want it.
The more verbose shell commands would be
{
read header
echo "$header"
i=0
while read line; do
echo "$line"
if (( ++i == 81 )); then
echo TER
i=0
fi
done
} < infile > outfile &&
mv outfile infile