adding a line to a text file

Shell Programming and Scripting
1

I have a tab delimited text file,

id   name       distance
1    3325167    0.334561754018
2    3290488    0.389444269458
3    3288794    0.392312701782
4    3347602    0.392532202097
5    3295355    0.394394169485

I need to add a line after the header line. The first and third field of that added line with both be the value 0 (hard coded). The middle field will be from a bash variable.

id   name       distance
0    $BASH_VAR  0.0
1    3325167    0.334561754018
2    3290488    0.389444269458
3    3288794    0.392312701782
4    3347602    0.392532202097
5    3295355    0.394394169485

I have looked at solutions in both sed and awk and can't seem to find the right thing.

I tried,

awk 'BEGIN {FS="\t"} {if (NR==2) print "0", "\t", $NAME, "\t", "0.0"; else print $0; }' TEMP > $OUTFILE

But that garbles the values of the inserted and existing lines.

LMHmedchem

2 
% BASH_VAR=hello 

% cat testfile   
id   name       distance
1    3325167    0.334561754018
2    3290488    0.389444269458
3    3288794    0.392312701782
4    3347602    0.392532202097
5    3295355    0.394394169485

% sed '1a\       
0    '$BASH_VAR'  0.0' testfile
id   name       distance
0    hello  0.0
1    3325167    0.334561754018
2    3290488    0.389444269458
3    3288794    0.392312701782
4    3347602    0.392532202097
5    3295355    0.394394169485

If you need right columns try:

BASH_VAR=`printf '%-9s' hello`
1 Like
3

I need tab delimited, so I got it to work with,

sed '1a\0\t'$BASH_VAR'\t0.0' TEMP > $OUTFILE

what is the meaning of the 1a\ notation? Does that mean to add the line at position 1? I thought you generally needed double quotes to preserve the value of the $VAR.

LMHmedchem

4

Yes.

Here it can work, but it won't in common case because sed and shell metachars can conflict (especially backslashes). So usual practice to embed shell variables in sed command is:

sed '...'$VAR'...'

Sorry for my English.