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I need to get the contents of a file but want to prevent an error if it does not exist.

Is it possible to do something like this?

cat my-file.txt || false
Jeff Schaller
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clarkk
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  • do you mean you don't want error to be outputed to screen? just output stderr to /dev/null – ralz Dec 28 '20 at 12:40
  • `cat my-file.txt 2>/dev/null` suppresses the error output or `[ -f my-file.txt ] && cat my-file.txt` skips the `cat` if the file is not present or, if you want a `true` exit status, use `[ ! -f my-file.txt ] || cat my-file.txt` – Bodo Dec 28 '20 at 12:42
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    Consider updating your question with an explanation of what you mean by "preventing an error". It's unclear what error you want to prevent. Is it the diagnostic message produced by `cat`, the fact that the exit status of your pipeline is non-zero, or do you want to prevent `cat` from even try to process an non-existent file? – Kusalananda Dec 28 '20 at 12:46

2 Answers2

5

You have a few options

  1. Avoid printing the file unless it exists, but still allow cat to complain if the file exists but cannot be opened

    [ -f my-file.txt ] && cat my-file.txt

  2. Avoid printing the error message generated if the file cannot be opened for whatever reason, by redirecting stderr to "nowhere"

    cat my-file.txt 2>/dev/null

  3. Avoid setting $? to a non-zero exit status, which would indicate that an error occurred.

     cat my-file.txt || true

In the first two cases, the next command can be a status test to check if the cat was successful. For example

cat my-file.txt 2>/dev/null
[ $? -ne 0 ] && echo 'There was an error accessing my-file.txt'

Further, this can then be wrapped into a more readable conditional, like this

if ! cat my-file.txt 2>/dev/null
then
    echo 'There was an error accessing my-file.txt'
fi

In the last case, there is no point in using the command in an if statement, as it's successfully hides the exit status of cat in such a way that the exit status of the compound command is always zero (it "prevents the error", in a way).

Kusalananda
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roaima
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-1

Close stderr with 2>&-:

cat my-file.txt 2>&- || false

U&L: Difference between 2>&-, 2>/dev/null, |&, &>/dev/null and >/dev/null 2>&1

GAD3R
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