Diff for "BashFAQ/090"

Differences between revisions 9 and 10

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 file

Some people insist on using the sed hammer to pound in all the screws:

sed "1iTEXTTOPREPEND" filename > tmp &&
mv tmp filename

Can also be done using here-docs either on command line or inside a script:

cat <<EOF >a.txt
This is line 0
$(cat a.txt)
EOF

There are lots of other solutions as well.

-  ⇤ ← Revision 9 as of 2011-03-15 17:02:32 → 
  Size: 903
  Editor: GreyCat
  Comment: ed
+   ← Revision 10 as of 2017-02-14 15:52:50 → ⇥
  Size: 1051
  Editor: peir-sab-antaeustravel-peer
  Comment: here-doc method added
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+or [[http://bash-hackers.org/wiki/doku.php?id=howto:edit-ed|ed]]:
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-or [[http://bash-hackers.org/wiki/doku.php?id=howto:edit-ed|ed]]:
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+Some people insist on using the `sed` hammer to pound in all the screws:
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-Some people insist on using the `sed` hammer to pound in all the screws:
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+Can also be done using here-docs either on command line or inside a script:

{{{
cat <<EOF >a.txt
This is line 0
$(cat a.txt)
EOF
}}}