Bash Nested Substring Removal (Extraction)?

Question

I have something similar in a script I'm writing:

CMD="/path/to/cmd,there.sh"
TMP="${CMD##*/}"
echo "${TMP%%,*}"

Is there a way to nest the substring removals in line 2 & 3, or produce the same result in one-line, in pure bash, without going out to another program? The length of ${CMD} is not static. To be clear, I want the output to be simply "cmd".

I've tried the below, with various forms of brackets and quotations, but get a syntax error. This is something (I think) was allowed but isn't in new versions of Bash.

echo "${${CMD##*/}%%,*}"

John Kugelman · Accepted Answer · 2018-01-24 19:58:47Z

1

Unfortunately, no, it's not possible to combine or nest string operations in bash.

answered Jan 24, 2018 at 19:58

John Kugelman

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Cyrus · Accepted Answer · 2018-01-24 20:16:53Z

1

With bash:

[[ $CMD =~ .*/([^,]*) ]] && echo ${BASH_REMATCH[1]}

answered Jan 24, 2018 at 20:16

Cyrus

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2 Comments

sjsam Over a year ago

Was wondering if you should make the regex ^.*/([^,]*).*$ for it to be more fault-proof? Or is just enough fine? I don't see a fail-case here, anyways.

Cyrus Over a year ago

@sjsam: That would probably be possible.

sjsam · Accepted Answer · 2018-01-24 20:12:54Z

0

Shell parameter substitution is primitive in that they don't provide functionalities like nesting. However, nobody prevents you from doing a sed thing here.

cmd="/path/to/cmd,there.sh" # Use lower-case identifiers for user variables
cmd=$(sed -E 's#^.*/([^,]+),.*$#\1#' <<<"$cmd")

The <<< enables the use of herestrings in bash.

answered Jan 24, 2018 at 20:12

sjsam

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Chris · Accepted Answer · 2018-01-26 11:48:53Z

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I've found that zsh actually supports nested string operations, so I actually switched the interpreter to zsh for my script and the below works fine:

echo "${${CMD##*/}%%,*}"

answered Jan 26, 2018 at 11:48

Chris

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helvete · Accepted Answer · 2023-02-17 08:26:57Z

0

If you want to write the script "in one line", just use ; or && to indicate the end of a line instead of a line-break:

CMD="/path/to/cmd,there.sh"; TMP="${CMD##*/}"; echo "${TMP%%,*}"

or

CMD="/path/to/cmd,there.sh" && TMP="${CMD##*/}" && echo "${TMP%%,*}"

A more elaborate answer about combining commands can be found below this question.

Disclaimer: I understand that it is debatable whether or not this is a one-liner. But if you are visiting this question looking for a way to throw this in bash, it may answer your question regardless.

edited Feb 17, 2023 at 8:26

helvete

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answered Feb 13, 2023 at 15:44

Wouter

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