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Alon
Asked: 2020-07-13 07:06:48 +0800 CST

Writing bash conditionalwith nested piped command

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The following bash command:

aws s3 ls s3://bucket/dir | grep _SUCCESS | wc -l

prints:

0

What I want is, when the result is indeed 0, to print FAILURE to the terminal.

This is what I've tried:

if [ aws s3 ls s3://bucket/dir | grep _SUCCESS | wc -l = 0]; then echo FAILURE; fi

but nothing is printed. it looks like it is waiting for more input.

bash

1 Answers

  1. Best Answer

    You should use command substitution:

    if [ $(aws s3 ls s3://bucket/dir | grep _SUCCESS | wc -l) -eq 0 ]
then 
    echo FAILURE;
fi

    or in a line:

    if [ $(aws s3 ls s3://bucket/dir | grep _SUCCESS | wc -l) -eq 0 ]; then echo FAILURE; fi

    Better solution as "@steeldriver" suggested use using grep's exit status :

    if aws s3 ls s3://bucket/dir | grep -q _SUCCESS; then echo FAILURE; fi

    or:

    aws s3 ls s3://bucket/dir | grep -q _SUCCESS || echo FAILURE
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