When installing, command in `postinst` always results in `$?` = `0`

Question

When installing, command in `postinst` always results in `$?` = `0`

I have a postinst script in my debian package:

#!/bin/bash

oqm-config -g system.hostname
RESULT="$?"
if [ "$RESULT" -eq 1 ]; then
  oqm-config -s system.hostname $(hostname).local "."
fi

This is intended to populate a config variable (if it doesn’t exist). These commands function outside of the install process:

$ sudo ./test.sh 
+ oqm-config -g system.hostname
ERROR: Config key not found: system.hostname
+ RESULT=1
+ [ 1 -eq 1 ]
+ hostname
+ oqm-config -s system.hostname oqm-demo.local .
{
    "system": {
        "hostname": "oqm-demo.local"
    },
    "captain": {},
    "snapshots": {
        "location": "/data/oqm-snapshots/",
        "numToKeep": 5,
        "frequency": "weekly"
    }
}

However, when executed during install, the return code from the initial oqm-config -g system.hostname is always 0 (or more accurately empty string? unsure why this particular error from an empty string, should be 0?):

Setting up open+quarter+master-manager-station+captain (1.0.18) ...
+ oqm-config -g system.hostname
ERROR: Config key not found: system.hostname
+ RESULT=0
+ '[' '' -eq 1 ']'
/var/lib/dpkg/info/open+quarter+master-manager-station+captain.postinst: line 5: [: : integer exp
ression expected

Am I missing something?

Building the debian file on Ubuntu 20.04, attempting install on 22.04

Debian file: https://github.com/Epic-Breakfast-Productions/OpenQuarterMaster/releases/tag/manager-station%2Bcaptain-1.0.18

File that makes the debian (I know it’s messy, but works [usually]): https://github.com/Epic-Breakfast-Productions/OpenQuarterMaster/blob/dev.388-fr-finish-keycloak-infra-component/software/Station-Captain/makeInstallers.sh#L107-L117

Asked By: Snappawapa

||

Source

Answer 1

The problem is this:

cat <<EOT >> "$buildDir/$debDir/DEBIAN/postinst"
#!/bin/bash

oqm-config -g system.hostname
RESULT=$?
if [ $RESULT -eq 1 ]; then
  oqm-config -s system.hostname $(hostname).local "."
fi

EOT

Bash performs parameter expansion, among other things, in heredocs:

If word is unquoted, all lines of the here-document are subjected to
parameter expansion, command substitution, and arithmetic expansion,
the character sequence newline is ignored, and ‘’ must be used
to quote the characters ‘’, ‘$’, and ‘`’.

(Here, word is the delimiter for the heredoc, EOT in this case.) That means that $? and $RESULT are expanded, and the heredoc writes the result of the expansion into the final input. You’re relying on this behaviour further down the script.

You can see this in the final postinst file:

$ curl -sL https://github.com/Epic-Breakfast-Productions/OpenQuarterMaster/releases/download/manager-station%2Bcaptain-1.0.18/open+quarter+master-manager-station+captain_1.0.18_all.deb | dpkg-deb --ctrl-tarfile - | tar -xO ./postinst
#!/bin/bash
set -x
oqm-config -g system.hostname
RESULT="0"
if [ "" -eq 1 ]; then
  oqm-config -s system.hostname oqm-dev.local "."
fi

# /usr/share/update-notifier/notify-reboot-required

Quote the delimiter to prevent this from happening:

cat <<'EOT' > "$buildDir/$debDir/DEBIAN/postinst"
#!/bin/bash

oqm-config -g system.hostname
RESULT=$?
if [ $RESULT -eq 1 ]; then
  oqm-config -s system.hostname $(hostname).local "."
fi
EOT

Answered By: muru