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Unix iMac shell terminal

sed -i 's/original/new/g' maths.tx  

Message returned: sed: -i may not be used with stdin

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Macs use the BSD version of utilities such as sed and date, which have their own idiosyncrasies.

In this specific case, the BSD build of sed mandates the extension for the backup file with -i, rather than it being optional, as in GNU sed.

As such:

sed -i .bak 's/needle/pin/g' haystack

The shown command will replace all instances of needle with pin in the file haystack, and the original file will be preserved in haystack.bak.

From the manual for the implementation of sed on a Mac:

-i extension
         Edit files in-place, saving backups with the specified extension.  If a zero-length extension is given, no backup will be saved.
         It is not recommended to give a zero-length extension when in-place editing files, as you risk corruption or partial content in
         situations where disk space is exhausted, etc.

As opposed to on a Linux host:

  -i[SUFFIX], --in-place[=SUFFIX]

          edit files in place (makes backup if SUFFIX supplied)

Note that "a zero-length extension" is distinct from "no extension". You can eschew the backup entirely, then, with:

sed -i '' 's/needle/pin/g' haystack
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  • that seem to work for my Mac sed -i '' – Kam Nov 3 '17 at 14:25
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    I'm glad it worked. Welcome to U&L! If this answer was helpful, please 'Accept' the answer so that people perusing questions know that it has been answered and can find a solution here. – DopeGhoti Nov 3 '17 at 16:14
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    @Kam Good! If this solves your issue, please consider accepting the answer. – Kusalananda Feb 8 '18 at 11:34
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    Accurate answer, just what I was looking for, I want to say that many utilities on the osx are different from GNU, for example, also grep utility. Please mark this answer as accepted. – user991 Oct 1 '20 at 18:36
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You have to specify a backup file, like:

sed -i .bak 's/original/new/g' maths.tx  

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