echo $SHELL
/bin/bash
echo $SHELL | wc -c
10
echo ${#SHELL}
9
The number of characters in $SHELL (e.g. /bin/bash) is 9, so why is the result is 10 when use wc -c?
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Ben Whaley
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disney82231
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This is kind of a duplicate question, but there is a nuance to this question that the other one does not have. – Ben Whaley Aug 25 '21 at 04:29
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@BenWhaley But answer can't possibly add anything new – Inian Aug 25 '21 at 04:30
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Actually it can, and I'm about to demonstrate that in a comment since the question is closed. – Ben Whaley Aug 25 '21 at 04:31
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2The nuance is that `${#SHELL}` is a [shell expansion](https://www.gnu.org/software/bash/manual/html_node/Shell-Expansions.html). The expansion performs the character count without the newline since `echo` hasn't actually run yet. So `echo ${#SHELL}` actually translates to `echo 9` with a trailing newline. – Ben Whaley Aug 25 '21 at 04:32
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1@BenWhaley Agreed. The Q is much better than the linked one. Feel free to add the answer – Inian Aug 25 '21 at 04:55
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:) Thanks @Inian! – Ben Whaley Aug 25 '21 at 05:02
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Perhaps also worth understanding why the output of `foo='a b c'; echo $foo | wc -c; echo ${#foo};` is 6 and 20. – William Pursell Aug 25 '21 at 05:23
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try `echo -n $SHELL | wc -c`, it'll result in 9 – phuclv Aug 25 '21 at 06:29
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1@disney82231 : You can find this out by replacing `wc -c` by `xxd`.... – user1934428 Aug 25 '21 at 06:30
2 Answers
5
It's because of the newline added by echo. When you type:
$ echo $SHELL
/bin/bash
$
echo prints a newline character, which is counted in the wc character count.
On the other hand, ${#SHELL} is a shell expansion. The shell performs the character count using an expansion without the extra newline character since echo hasn't actually run yet. So echo ${#SHELL} actually translates to echo 9. The 9 is printed with a trailing new line added by echo.
Ben Whaley
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I'm strongly recommend to use shell expansion. Here ${#SHELL}
Warning with wc -c that count BYTES. Not characters.
If you want to count characters with it, use wc -m
It's very important when you not only use ASCII chars table and an UTF-8 terminal (or whatever multibytes charset) or in I18N context
Try this:
$ x="/x/♤/é/"
$ echo ${#x}
$ echo -n "$x" | wc -c
$ echo -n "$x" | wc -m
Arnaud Valmary
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