How to insert a column at the start of a txt file using awk?-CodePudding

How to insert a column at the start of a txt file running from 1 to 2059 which corresponds to the number of rows I have in my file using awk. I know the command will be something like this:

awk '{$1=" "}1' File

Not sure what to put between the speech-marks 1-2059?

I also want to include a header in the header row so 1 should only go in the second row technically.

**ID**     Heading1
RQ1293939    -7.0494
RG293I32SJ   -903.6868
RQ19238983   -0899977
rq747585950   988349303

FID  **ID**     Heading1
1    RQ1293939    -7.0494
2    RG293I32SJ   -903.6868
3    RQ19238983   -0899977
4    rq747585950   988349303

So I need to insert the FID with 1 - 2059 running down the first column

CodePudding user response：

What you show does not work, it just replaces the first field ($1) with a space and prints the result. If you do not have empty lines try:

awk 'NR==1 {print "FID\t" $0; next} {print NR-1 "\t" $0}' File

Explanations:

NR is the awk variable that counts the records (the lines, in our case), starting from 1. So NR==1 is a condition that holds only when awk processes the first line. In this case the action block says to print FID, a tab (\t), the original line ($0), and then move to next line.
The second action block is executed only if the first one has not been executed (due to the final next statement). It prints NR-1, that is the line number minus one, a tab, and the original line.

If you have empty lines and you want to skip them we will need a counter variable to keep track of the current non-empty line number:

awk 'NR==1 {print "FID\t" $0; next} NF==0 {print; next} {print   cnt "\t" $0}' File

Explanations:

NF is the awk variable that counts the fields in a record (the space-separated words, in our case). So NF==0 is a condition that holds only on empty lines (or lines that contain only spaces). In this case the action block says to print the empty line and move to the next.
The last action block is executed only if none of the two others have been executed (due to their final next statement). It increments the cnt variable, prints it, prints a tab, and prints the original line.
Uninitialized awk variables (like cnt in our example) take value 0 when they are used for the first time as a number. cnt increments variable cnt before its value is used by the print command. So the first time this block is executed cnt takes value 1 before being printed. Note that cnt would increment after the printing.

CodePudding user response：

Assuming you don't really have a blank row between your header line and the rest of your data:

awk '{print (NR>1 ? NR-1 : "FID"), $0}' file

Use awk -v OFS='\t' '...' file if you want the output to be tab-separated or pipe it to column -t if you want it visually tabular.