text-processing – Easiest Way to Add a String at the Beginning of Every Line from Command Line

awkperlsedtext processing

I am looking for a way to add some string to the beginning of every line (same string for every line).
Not something customizable but rather something that will be easy to remember and available on every POSIX-compliant platform (and every shell as well).

Best Answer

You can use sed:

sed -i 's/^/your_string /' your_file

Thanks to Stephane and Marco's comments, note that the -i option isn't POSIX. A POSIX way to do the above would be

sed 's/^/your_string /' your_file > tmp_copy && mv tmp_copy your_file

or perl:

perl -pi -e 's/^/your_string /' your_file

Explanation

Both commands perform a regex substitution, replacing the beginning of a line (^) with your desired string. The -i switch in both commands makes sure the file is edited in place (i.e. the changes are reflected in the file instead of printed to stdout).

sed should be available on any POSIX-compliant OS and perl should be available on most modern Unices except perhaps for the ones that have gone through the effort of removing it.

Related Solutions

Text Processing – Remove Line Containing Certain String and the Following Line

If you have GNU sed (so non-embedded Linux or Cygwin):

sed '/bar/,+1 d'

If you have bar on two consecutive lines, this will delete the second line without analyzing it. For example, if you have a 3-line file bar/bar/foo, the foo line will stay.

Add and Remove Text from Same Place on Every Line in Emacs

The easiest way to do this is with the rectangle commands.

Go to the first line of the buffer (or more generally the first line where you want to insert text) and move to the column where you want to insert the text. Go to the last line and move to the same column (there's no built-in way to do that). Type C-x r t (string-rectangle) and type the string you want to insert.

You can use the following function to move the cursor to the same column as the mark:

(defun move-to-mark-column ()
  (interactive "@")
  (move-to-column (save-excursion
                    (goto-char (mark))
                    (current-column))))

If you want to move to a column by number, there's move-to-column: C-u 42 M-x move-to-column RET. Unless you bind this to a key, it's shorter to move to the beginning of the line and then by character count (Home C-u 42 Right), but this can move to the next line if the count is too high, whereas move-to-column leaves you at the end of the line in this case. Also move-to-column behaves differently if there are tabs or split lines.

If the point and mark aren't on the same column, they're opposite corner of a rectangle. The rectangle command affect all the characters inside that rectangle. string-rectangle erases the rectangle and puts the specified text on each line instead. C-x r d erases the rectangle. You can also copy-paste (C-x r M-w, C-x r k, C-x r y to copy/kill/yank) and insert or fill with rectangles (C-x r o, C-x r c to open/clear with spaces), and more.

Best Answer

Related Solutions

Text Processing – Remove Line Containing Certain String and the Following Line

Add and Remove Text from Same Place on Every Line in Emacs

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