How to insert a '#' in the first position of all the files?

Shell Programming and Scripting
1

Hi All,

how to insert a '#' in the first position of all the files based on a certain condition.

I tried this:

cat /bin/user/input_file.txt | while read a 
do
b=`sed 's/.*song=good.*/\#&/g' $a `
echo $b > /bin/user/new/output_file.txt
done

input_file.txt has list of names of 10 files.. the sed condition will check all the files and search for the condition ( song=good ) and then inserts a # and then redirects the output to a new directory and a new file output_file.txt..

when i ran this,i am not able to get the desired output.

required output:

file 1:

1.elvis presly 1,5,6,song=bad;
#2.richie,2,6,8,song=good;
3.benaud,3,9,8,song=bad;

output which i am getting:

1.elvis presly 1,5,6,song=bad; #2.richie,2,6,8,song=good; 3.benaud,3,9,8,song=bad;

please help me on this

2 
sed 's/.*song=good;/#&/' input.txt > output.txt
3

Using awk

awk '/song=good/ {$0="#"$0} 1' infile
4

Hi,

Its not in the problem of the code r the command..
and thats not only one file.. it has a set of files which is passed in the loop..the same name in which the file is given the output shud be sent in the same name to a different directory.. thats the prob i have.. moreover will it be different from linux and unix environment..

5

Do you want the output of all the files in input_file.txt to be in one single file? output_file.txt?

The following code will store the files after modification to a new directory with its respective file names suffixed with the extension "new"

while read line
do
  sed 's/.*song=good;/#&/' $line > /bin/user/new/$line.new
done < /bin/user/input_file.txt

--ahamed

6

When you use the $(command) and `command` forms of command substitution, the trailing <newline> character (if there is one) will be dropped from the output. There doesn't seem to be any need to assign the output of sed to a variable; just let sed write directly into your output file. The following would seem to do what you want:

sed 's/.*song=good.*/\#&/' $(cat /bin/user/input_file.txt) > /bin/user/new/output_file.txt

This should work on any Linux or UNIX System as long as you are using a shell (such as a Korn shell [ksh] or bash) that recognizes minimal requirements specified by the POSIX standards and the Single UNIX Specifications as long as the pathnames stored in input_file.txt do not contain any whitespace characters.

Note also that using:

echo $b

to print a line of output will produce different output when using different versions of echo if the variable b contains any tab characters, any occurrences of multiple adjacent spaces, starts with a minus sign, or contains any backslash characters. If you want to copy the contents of a variable to a file adding a <newline> character to the end of it (without altering spacing, leading minus signs, and backslash characters), you could replace the echo command with:

printf "%s\n" "$b"

And, finally, note that using:

echo $b > /bin/user/new/output_file.txt

will only save the output from the last file processed. Each time you use > as a redirection operator in the shell, all previous output in the destination file will be replaced.