Append the output of sed to a file

Question

I have two scripted files, say file1 and file2. I want to take the content of file1, change character a to A in file1 and append the output to file2 without modifying the content of file1. I'm trying with:

sed -i ‘s/a/A/g’ file1 >> file2

but this just changes the a to A in file1.

... fyi sed has a y command that is more idiomatic for single character replacements: sed 'y/a/A/' file1 >> file2 — steeldriver, Sep 03 '22 at 17:45
@steeldriver Does using y pose an advantage to using the s command? — BeastOfCaerbannog, Sep 03 '22 at 17:56
@BeastOfCaerbannog I don't know tbh - in theory it could be more efficient since it doesn't need to invoke a regular expression engine, but whether it's actually implemented more efficiently is a different matter. Probably the OP should be using tr rather than sed in this application. — steeldriver, Sep 03 '22 at 18:18

BeastOfCaerbannog · Accepted Answer · 2022-09-03T18:11:43.457

Just remove the -i flag:

sed 's/a/A/g' file1 >> file2

The -i flag is used to edit the specified file in place, so it does just that to file1. From man sed:

-i[SUFFIX], --in-place[=SUFFIX]
   edit files in place (makes backup if SUFFIX supplied)

The reason you get nothing appended to file2 when you use -i is that >> is used to append stdout to the specified file. But since file1 is edited in place due to -i, no output is generated, so nothing is appended to file2.

Append the output of sed to a file

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