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Prepend a text to a file.

Terminal - Prepend a text to a file.
sed -i '1s/^/text to prepend\n/' file1
2011-06-25 12:02:11
User: xeor
Functions: sed
4
Prepend a text to a file.

Using the sed -i (inline), you can replace the beginning of the first line of a file without redirecting the output to a temporary location.

Alternatives

There is 1 alternative - vote for the best!

Terminal - Alternatives
echo "text to prepend" | cat - file
prepend () { array=("$@"); len=${#array[@]}; file=${array[$len-1]}; text=${array[@]:0:$len-1}; printf '%s\n' 0a "$text" . w | ed -s "$file"; }
2013-12-09 21:59:26
User: zlemini
Functions: ed printf
Tags: sed replace
3

Syntax:

$ prepend content to add [filename]

Uses ed, so no temp files created.

sed -i 's/^/ls -l /' output_files.txt
2013-10-07 15:12:53
User: sonic
Functions: sed
Tags: sed replace
1

The original command is great, but I often want to prepend to every line.

echo "text to prepend" | cat - file
2013-12-18 15:54:17
User: leni536
Functions: cat echo
Tags: cat replace
1

Prepend text to a file. It doen't need temporary files, ed or sed.

Know a better way?

If you can do better, submit your command here.

What others think

Sed has the -i switch for "in-place" editing. First of all, only some implementations of sed (GNU sed and BSD sed AFAIK) support -i. It's a nonstandard extension, and as such not universally available.

According to the documentation (at least GNU sed's), what sed does when -i is specified is create a temporary file, send output to that file, and at the end, that file is renamed to the original name. This can be verified with strace; even without strace, a simple "ls -i" of the file before and after sed operates will show two different inode numbers.

Comment by RanyAlbeg 284 weeks and 6 days ago

But at least it does it for us.

Comment by kaedenn 284 weeks and 6 days ago

In a nonstandard way. And it makes sense, since sed is a STREAM editor so the "in-place" option *should* be a nonstandard one by that logic.

Comment by RanyAlbeg 284 weeks and 5 days ago

A good use of this would be:

sed -i '1s/^/#!\/usr\/bin\/env python\n\n/' myscript.py
Comment by ewilson 284 weeks and 4 days ago
echo "text to prepend

$(cat output.log)" > output.log

Comment by lapinpt 93 weeks and 5 days ago
echo "text to prepend" | cat - output.log | sponge output.log
Comment by lapinpt 93 weeks and 5 days ago

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Comment by xiaozhengm 35 weeks and 1 day ago

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