How to add string at a specific position in each line

Question

With

awk '{ printf "%-15s %s\n", $1, $2 }' renamed | sort -V

... I get good output from the file renamed.

It looks like:

file1           file1.new

But I want to have the output changed to this:

file1           -->  file1.new

I want to add --> at position 15 in each line.

How to do that?

Answer 1

The printf format string %-15s %s\n specifies that you want to output two strings delimited by a space and terminated by a newline character.

The first string should be given a width of 15 characters, and the minus sign signifies that it should be left-justified within those 15 characters (the remaining characters to the right of the string will be filled out with spaces).

To insert --> in front of the second string, after the single space, just modify the format to %-15s --> %s\n.

Example of this:

$ printf '%s\n' "one thing" "another thing" | awk '{ printf "%-15s %s\n", $1, $2 }'
one             thing
another         thing

$ printf '%s\n' "one thing" "another thing" | awk '{ printf "%-15s -->  %s\n", $1, $2 }'
one             -->  thing
another         -->  thing

Note that the --> is actually added at position 17, not 15. Position 15 is reserved for the first string while position 16 will have that space character in the formatting string. To add --> at position 15, you would need to reduce the space for the first string to 13: %-13s --> %s\n.

Answer 2

Consider using column to determine the appropriate first field width instead of hard-coding 15 so it can handle fields longer than 15 chars if necessary, e.g. using any version of column:

$ cat renamed
file1 file1.new
12345678951234567890 file2.new

$ column -t renamed
file1                 file1.new
12345678951234567890  file2.new

$ column -t renamed | sed 's/  */&-->  /'
file1                 -->  file1.new
12345678951234567890  -->  file2.new

If you have GNU column then it has a -o option to specify the output field separator so then you don't need the pipe to sed:

$ column -t -o '  -->  ' renamed
file1                 -->  file1.new
12345678951234567890  -->  file2.new

It can also handle blanks inside the fields if your fields are tab-separated by adding -s$'\t' or there are all sorts of other things we could do to handle all sorts of different input, ask a new question with more details on your input format if you need more help.