[Bug 2051735] [NEW] fails to use `file` to determine file type as claimed

[Joe Strout]

Public bug reported:

The man page for run-mailcap claims " If no mime-type is found, a last attempt will be done by running
the file command, if available."  But this does not actually work.  Example:

1. Find or make a plain text file called LICENSE.
2. Use the `file` command in the same way as run-mailcap to check its type:
```
   file -b --mime-type -e tokens -L -z LICENSE
```
It reports "text/plain".
3. Now try `run-mailcap LICENSE` (or any equivalent, such as `edit LICENSE`).  I get:
Warning: unknown mime-type for "LICENSE" -- using "application/octet-stream"
Error: no "view" mailcap rules found for type "application/octet-stream"

If you comment out the `if` and `}` lines in /usr/bin/run-mailcap (lines
301 and 306), and try the run-mailcap command again, it works.

So, somehow the test for whether file is available is failing within the
script, even though `command -v file` works just fine on the command
line.

Description:	Ubuntu 22.04.3 LTS
Release:	22.04

mailcap:
  Installed: 3.70+nmu1ubuntu1
  Candidate: 3.70+nmu1ubuntu1
  Version table:
 *** 3.70+nmu1ubuntu1 500
        500 http://us-east1.gce.archive.ubuntu.com/ubuntu jammy/main amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: mailcap 3.70+nmu1ubuntu1
ProcVersionSignature: Ubuntu 6.2.0-1019.21~22.04.1-gcp 6.2.16
Uname: Linux 6.2.0-1019-gcp x86_64
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckResult: unknown
CloudArchitecture: x86_64
CloudID: gce
CloudName: gce
CloudPlatform: gce
CloudRegion: us-east1
CloudSubPlatform: metadata (http://metadata.google.internal/computeMetadata/v1/)
Date: Tue Jan 30 21:24:13 2024
PackageArchitecture: all
SourcePackage: mailcap
UpgradeStatus: Upgraded to jammy on 2024-01-04 (26 days ago)

** Affects: mailcap (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug jammy uec-images

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https://bugs.launchpad.net/bugs/2051735

Title:
  fails to use `file` to determine file type as claimed

Status in mailcap package in Ubuntu:
  New

Bug description:
  The man page for run-mailcap claims " If no mime-type is found, a last attempt will be done by running
  the file command, if available."  But this does not actually work.  Example:

  1. Find or make a plain text file called LICENSE.
  2. Use the `file` command in the same way as run-mailcap to check its type:
  ```
     file -b --mime-type -e tokens -L -z LICENSE
  ```
  It reports "text/plain".
  3. Now try `run-mailcap LICENSE` (or any equivalent, such as `edit LICENSE`).  I get:
  Warning: unknown mime-type for "LICENSE" -- using "application/octet-stream"
  Error: no "view" mailcap rules found for type "application/octet-stream"

  If you comment out the `if` and `}` lines in /usr/bin/run-mailcap
  (lines 301 and 306), and try the run-mailcap command again, it works.

  So, somehow the test for whether file is available is failing within
  the script, even though `command -v file` works just fine on the
  command line.

  Description:	Ubuntu 22.04.3 LTS
  Release:	22.04

  mailcap:
    Installed: 3.70+nmu1ubuntu1
    Candidate: 3.70+nmu1ubuntu1
    Version table:
   *** 3.70+nmu1ubuntu1 500
          500 http://us-east1.gce.archive.ubuntu.com/ubuntu jammy/main amd64 Packages
          100 /var/lib/dpkg/status

  ProblemType: Bug
  DistroRelease: Ubuntu 22.04
  Package: mailcap 3.70+nmu1ubuntu1
  ProcVersionSignature: Ubuntu 6.2.0-1019.21~22.04.1-gcp 6.2.16
  Uname: Linux 6.2.0-1019-gcp x86_64
  ApportVersion: 2.20.11-0ubuntu82.5
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CloudArchitecture: x86_64
  CloudID: gce
  CloudName: gce
  CloudPlatform: gce
  CloudRegion: us-east1
  CloudSubPlatform: metadata (http://metadata.google.internal/computeMetadata/v1/)
  Date: Tue Jan 30 21:24:13 2024
  PackageArchitecture: all
  SourcePackage: mailcap
  UpgradeStatus: Upgraded to jammy on 2024-01-04 (26 days ago)

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