UNIX for Beginners Questions & Answers

Hi,

I've got text files (say file1 and file2) in a directory (say directory1) with several columns like this:

Code:

a b c d
a b c d

Code:

e f g h
e f g h

I need to add a header to the files in directory1 and the names of the columns must contain an identifier from another text file (say file3) like this:

Code:

12
34

So, the output should be like this:

Code:

12.X 12.Y 12.Z 12.T  
a b c d
a b c d

Code:

34.X 34.Y 34.Z 34.T  
e f g h
e f g h

In reality, file3 has over 6000 entries and there are more than 2 files that need a header, so I've written the following loop:

Code:

for a in $(ls directory1);
do
for i in $(cat file1);
do
sed '1 i\${i}.X ${i}.Y ${i}.Z ${i}.T \' ${a} > ${a}withheader;
done
done

However, the added headers look like this:

Code:

${i}.X ${i}.Y ${i}.Z ${i}.T

I suppose the '' prevent the shell to read the loop syntax. Is there anyway to avoid that? Or any other solution to add the headers?

Many thanks in advance!

---------- Post updated 08-18-16 at 01:20 AM ---------- Previous update was 08-17-16 at 11:32 PM ----------

I've figured it out, I just need to put '' around the looping variable:

Code:

sed '1 i\'${i}'.X '${i}'.Y '${i}'.Z '${i}'.T \' ${a} > ${a}withheader

Thank you!

Moderator's Comments:

Please use CODE (not HTML) tags as required by forum rules!

So - just to get it right - for n > 2 files, you want to create m > 6000 new files each, resulting in n * m ( > 18000) files? Quite some opening and writing files ...
How about (untested, may need some polishing):

Code:

while read i
  do for a in directory1/*
        do echo $i.X $i.Y $i.z $i.T | cat - ${a} > ${a}withheader
        done
  done < file3

As far as I have understood the task is more a merge:
for each file you need to read one line from the number file. Nested loops are not appropriate (and leads to inefficiency).
With shell-builtins

Code:

#!/bin/sh
for a in directory1/*
do
  read i <&3
  {
  echo "${i}.X ${i}.Y ${i}.Z ${i}.T"
  cat "$a"
  } > "${a}withheader"
done 3< file3

The file3 is opened with an extra descriptor 3 where the read reads one line from (could have been just the < and simple read here, but is safer in case some more code would read from stdin).
Like the for-done block gets an opened input file, there is an artificial { block } that gets an opened destination file as stdout.

@MadeinGermany: Wouldn't your interpretation (that I pondered on as well) mean that there need to be 6000 ( OK, OK - 6000 IS > 2!) input files as well?

Yes indeed, if the number(ID) file is file3 with 6000 lines, this would mean (up to) 6000 input files.
However, the sample script in post#1 seems to take file1 as the number file...