Wrong assumption about missing '-' arg if pipingStdin detected

[aleksandr-vin]

Describe the bug
When yq is placed inside a bigger block where other commands read from stdin which is piped to that whole block, yq is egoistically reading the stdin.

The commit 703418d adds "-" to the args when pipingStdin is detected.

Version of yq: 4.20.1
Operating system: mac
Installed via: homebrew

Command

Problem appears when used in blocks, so the minimal script that reproduces the problem:

#!/usr/bin/env bash
set -e
set -x

cat >foo.json <<EOF
{}
EOF

ls foo*
printf "1\n2\n" | while read -r f
do
    yq -P '.' "foo.json" >"foo-$f.yaml"
done
find . -type f -depth 1 -name 'foo-*.yaml' -print -exec cat {} ";"

Actual behavior

The read of the while block is intended to read 1 and 2 on each iteration of while but in practice there is nothing left for read after yq finished his one call, and 2 can be found in foo-1.yaml:

+ cat
+ ls foo.json
foo.json
+ printf '1\n2\n'
+ read -r f
+ yq -P . foo.json
+ read -r f
+ find . -type f -depth 1 -name 'foo-*.yaml' -print -exec cat '{}' ';'
./foo-1.yaml
{}
---
2

Expected behavior

+ cat
+ ls foo.json
foo.json
+ printf '1\n2\n'
+ read -r f
+ yq -P . foo.json
+ read -r f
+ yq -P . foo.json
+ read -r f
+ find . -type f -depth 1 -name 'foo-*.yaml' -print -exec cat '{}' ';'
./foo-1.yaml
{}
./foo-2.yaml
{}

Workaround

In such cases when yq is involved in a block of commands which has its stdin piped (but not for yq) the egoism of yq can be fed with </dev/null. So the line in the before mentioned script would be:

  yq -P '.' </dev/null "foo.json" >"foo-$f.yaml"

[mikefarah]

Yeah I can replicate that - but not actually sure how to fix it.

Any golang experts? I'm doing this to detect if there's stdin:

stat, _ := os.Stdin.Stat()
pipingStdIn := (stat.Mode() & os.ModeCharDevice) == 0

which from what I read is the correct way, but yes it appears to be too eager :/

[aleksandr-vin]

Maybe adding - only if no files are on the args list?

[mikefarah]

...that's a great idea!

…

________________________________ From: Aleksandr Vinokurov ***@***.***> Sent: Thursday, February 17, 2022 5:51:07 PM To: mikefarah/yq ***@***.***> Cc: Mike Farah ***@***.***>; Comment ***@***.***> Subject: Re: [mikefarah/yq] Wrong assumption about missing '-' arg if `pipingStdin` detected (Issue #1115) Maybe adding - only if no files are on the args list? — Reply to this email directly, view it on GitHub<#1115 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AAIZHNK4RMKXOJMSRLSEST3U3SLFXANCNFSM5OS75OQA>. Triage notifications on the go with GitHub Mobile for iOS<https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android<https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you commented.Message ID: ***@***.***>

[mikefarah]

Fixed in 4.20.2