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Scenario:

$ cat xxx.txt | od -c
0000000   x  \n   x  \n
0000004

$ value=""

# 1st iteration
$ value+="$(<xxx.txt)" ; echo "$value" | od -c
0000000   x  \n   x  \n
0000004

# 2nd iteration
$ value+="$(<xxx.txt)" ; echo "$value" | od -c
0000000   x  \n   x   x  \n   x  \n
0000007

At the 2nd iteration we see that \n after the 2nd x is lost. Why? How to prevent this?

The expected output is:

0000000   x  \n   x  \n   x  \n   x  \n
0000007
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  • 2
    That "1st iteration" output is actually misleading (well, as is the second). The final newline you see is from echo. Use printf %s "$value" instead. Commented May 23, 2024 at 10:50
  • @muru Thanks. Then why after value="$(<xxx.txt)" the value doesn't contain the last newline character? How to fix? Commented May 23, 2024 at 11:27
  • The "why" is explained in the duplicate: command substitution $(...) removes trailing newlines. Sadly there is no fix, command substitution always does that. You can, however, try something like: value+=$(cat xxx.txt; printf x); value=${value%x} (add a trailing character to protect the newline, then remove it afterwards). Commented May 23, 2024 at 11:33
  • @muru Indeed, command substitution $(...) removes trailing newlines. TIL. FYI: user Stéphane Chazelas recommends using / rather than x. Commented May 23, 2024 at 18:13

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