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Size: 448
Comment: How do I prepend a text to a file (the opposite of >>)?
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← Revision 12 as of 2017-02-14 19:48:12 ⇥
Size: 903
Comment: Sorry, but the substitution-inside-here-doc is not safe. There's no guarantee bash will slurp the old content before overwriting it.
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| You cannot do it with bash redirections alone; the opposite of `>>` does not exist.... | |
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| You cannot do it with bash redirections only, ie the opposite of >> does not exist. You can use an editor: |
To insert content at the beginning of a file, you can use an editor, for example `ex`: |
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| ed -s file << EOF i |
ex file << EOF 0a |
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| you can use things like: | or [[http://bash-hackers.org/wiki/doku.php?id=howto:edit-ed|ed]]: {{{ printf '%s\n' 0a "line 1" "line 2" . w | ed -s file }}} `ex` will also add a newline character to the end of the file if it's missing. Or you can rewrite the file, using things like: |
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| or a gazillion of other solutions | Some people insist on using the `sed` hammer to pound in all the screws: {{{ sed "1iTEXTTOPREPEND" filename > tmp && mv tmp filename }}} There are lots of other solutions as well. |
How do I prepend a text to a file (the opposite of >>)?
You cannot do it with bash redirections alone; the opposite of >> does not exist....
To insert content at the beginning of a file, you can use an editor, for example ex:
ex file << EOF 0a header line 1 header line 2 . w EOF
or ed:
printf '%s\n' 0a "line 1" "line 2" . w | ed -s file
ex will also add a newline character to the end of the file if it's missing.
Or you can rewrite the file, using things like:
{ echo line; cat file ;} >tmpfile && mv tmpfile file
echo line | cat - file > tmpfile && mv tmpfile fileSome people insist on using the sed hammer to pound in all the screws:
sed "1iTEXTTOPREPEND" filename > tmp && mv tmp filename
There are lots of other solutions as well.