How to insert a text at the beginning of a file?

Question

So far I've been able to find how to add a line at the beginning of a file but that's not exactly what I want. I'll show it on a example

File content

some text at the beginning

Result

<added text> some text at the beginning

It's similar but I don't want to create any new line with it...

I would like to do this with sed if possible.

Answer 1

Hi with carriage return:

sed -i '1s/^/your text\n/' file

Answer 2

sed can operate on an address:

$ sed -i '1s/^/<added text> /' file

What is this magical 1s you see on every answer here? Line addressing!.

Want to add <added text> on the first 10 lines?

$ sed -i '1,10s/^/<added text> /' file

Or you can use Command Grouping:

$ { echo -n '<added text> '; cat file; } >file.new
$ mv file{.new,}

Answer 3

PROBLEM: tag a file, at the top of the file, with the base name of the parent directory.

I.e., for

/mnt/Vancouver/Programming/file1

tag the top of file1 with Programming.

SOLUTION 1 -- non-empty files:

bn=${PWD##*/}    ## bn: basename

sed -i '1s/^/'"$bn"'\n/' <file>

1s places the text at line 1 of the file.

SOLUTION 2 -- empty or non-empty files:

The sed command, above, fails on empty files. Here is a solution, based on https://superuser.com/questions/246837/how-do-i-add-text-to-the-beginning-of-a-file-in-bash/246841#246841

printf "${PWD##*/}\n" | cat - <file> > temp && mv -f temp <file>

Note that the - in the cat command is required (reads standard input: see man cat for more information). Here, I believe, it's needed to take the output of the printf statement (to STDIN), and cat that and the file to temp ... See also the explanation at the bottom of http://www.linfo.org/cat.html.

I also added -f to the mv command, to avoid being asked for confirmations when overwriting files.

To recurse over a directory:

for file in *; do printf "${PWD##*/}\n" | cat - $file > temp && mv -f temp $file; done

Note also that this will break over paths with spaces; there are solutions, elsewhere (e.g. file globbing, or find . -type f ... -type solutions) for those.

ADDENDUM: Re: my last comment, this script will allow you to recurse over directories with spaces in the paths:

#!/bin/bash

## https://stackoverflow.com/questions/4638874/how-to-loop-through-a-directory-recursively-to-delete-files-with-certain-extensi

## To allow spaces in filenames,
##   at the top of the script include: IFS=$'\n'; set -f
##   at the end of the script include: unset IFS; set +f

IFS=$'\n'; set -f

# ----------------------------------------------------------------------------
# SET PATHS:

IN="/mnt/Vancouver/Programming/data/claws-test/corpus test/"

# https://superuser.com/questions/716001/how-can-i-get-files-with-numeric-names-using-ls-command

# FILES=$(find $IN -type f -regex ".*/[0-9]*")        ## recursive; numeric filenames only
FILES=$(find $IN -type f -regex ".*/[0-9 ]*")         ## recursive; numeric filenames only (may include spaces)

# echo '$FILES:'                                      ## single-quoted, (literally) prints: $FILES:
# echo "$FILES"                                       ## double-quoted, prints path/, filename (one per line)

# ----------------------------------------------------------------------------
# MAIN LOOP:

for f in $FILES
do

  # Tag top of file with basename of current dir:
  printf "[top] Tag: ${PWD##*/}\n\n" | cat - $f > temp && mv -f temp $f

  # Tag bottom of file with basename of current dir:
  printf "\n[bottom] Tag: ${PWD##*/}\n" >> $f
done

unset IFS; set +f

Answer 4

To insert just a newline:

sed '1i\\'

Answer 5

Just for fun, here is a solution using ed which does not have the problem of not working on an empty file. You can put it into a shell script just like any other answer to this question.

ed Test <<EOF
a

.
0i
<added text>
.
1,+1 j
$ g/^$/d
wq
EOF

The above script adds the text to insert to the first line, and then joins the first and second line. To avoid ed exiting on error with an invalid join, it first creates a blank line at the end of the file and remove it later if it still exists.

Limitations: This script does not work if <added text> is exactly equal to a single period.

Answer 6

You can use cat -

printf '%s' "some text at the beginning" | cat - filename