Use SHELL environment variable before falling back to /bin/bash #81

Copilot · 2026-02-01T19:30:30Z

On systems like NixOS, bash is not located at /bin/bash. The wp shell command was hardcoded to this path, causing failures despite the shell being available at $SHELL.

Changes

Shell detection priority in REPL.php:
1. WP_CLI_CUSTOM_SHELL (explicit override)
2. SHELL (system default) ← new
3. /bin/bash (fallback)
Test coverage: Added scenario verifying SHELL environment variable is respected

// Before
if ( getenv( 'WP_CLI_CUSTOM_SHELL' ) ) {
    $shell_binary = getenv( 'WP_CLI_CUSTOM_SHELL' );
} else {
    $shell_binary = '/bin/bash';
}

// After
if ( getenv( 'WP_CLI_CUSTOM_SHELL' ) ) {
    $shell_binary = getenv( 'WP_CLI_CUSTOM_SHELL' );
} elseif ( getenv( 'SHELL' ) ) {
    $shell_binary = getenv( 'SHELL' );
} else {
    $shell_binary = '/bin/bash';
}

Aligns with how wp --info detects the shell.

Original prompt

This section details on the original issue you should resolve

<issue_title>Shell binary not getting detected correctly?</issue_title>
<issue_description>## Bug Report

Yes, I reviewed the contribution guidelines.

Yes, more specifically, I reviewed the guidelines on how to write clear bug reports.

The shell binary '/bin/bash' is not valid.

The wp --info command shows the correct Shell, but wp shell does not seem to find it. Since it's not in /bin/bash
[sergio@samara:/var/www/nerdpress]$ wp --info
OS:     Linux 6.6.32 wp-cli/shell-command#1-NixOS SMP PREEMPT_DYNAMIC Sat May 25 14:22:56 UTC 2024 x86_64
Shell:  /run/current-system/sw/bin/bash
PHP binary:     /nix/store/swkmyv7mplz46vlr9jyk7qlp2lxv19z0-php-with-extensions-8.2.19/bin/php
PHP version:    8.2.19
php.ini used:   /nix/store/6g69kphwfkdx4p2qn1fgwm888l15cpz7-wp-cli-2.10.0/etc/php.ini
MySQL binary:   /run/current-system/sw/bin/mysql
MySQL version:  mysql  Ver 15.1 Distrib 10.11.6-MariaDB, for Linux (x86_64) using readline 5.1
SQL modes:      STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
WP-CLI root dir:        phar://wp-cli.phar/vendor/wp-cli/wp-cli
WP-CLI vendor dir:      phar://wp-cli.phar/vendor
WP_CLI phar path:       /var/www/nerdpress
WP-CLI packages dir:
WP-CLI cache dir:       $XDG_CACHE_HOME/wp-cli
WP-CLI global config:
WP-CLI project config:
WP-CLI version: 2.10.0

[sergio@samara:/var/www/nerdpress]$ wp shell
Error: The shell binary '/bin/bash' is not valid. You can override the shell to be used through the WP_CLI_CUSTOM_SHELL environment variable.

[sergio@samara:/var/www/nerdpress]$ php -a
Interactive shell

php > var_dump( is_file( '/run/current-system/sw/bin/bash' ) );
bool(true)
php > var_dump( is_readable( '/run/current-system/sw/bin/bash' ) );
bool(true)
php > exit
Describe how other contributors can replicate this bug

Have get( 'SHELL' ); return something other than /bin/bash

Run wp shell

Provide a possible solution

Seems that the wp cli info command gets the shell binary using:
getenv( 'SHELL' )

Where wp shell uses getenv( 'WP_CLI_CUSTOM_SHELL' ) to check for a "custom shell", then assumes /bin/bash is it isn't set.

Why not use $shell_binary = getenv( 'SHELL' ); instead of $shell_binary = '/bin/bash';

</issue_description>

Comments on the Issue (you are @copilot in this section)
@swissspidy `WP_CLI_CUSTOM_SHELL` is an environment variable accessed via `getenv`. It is not a PHP constant. So you would do this instead:
WP_CLI_CUSTOM_SHELL=/run/current-system/sw/bin/bash wp shell
```</body></comment_new>
<comment_new><author>@swissspidy</author><body>
Good question. Maybe @schlessera or @danielbachhuber have some context about why the current default is a hardcoded `/bin/bash` and not `getenv( 'SHELL' )`. It sounds like a reasonable enhancement at first glance.</body></comment_new>
<comment_new><author>@danielbachhuber</author><body>
I don't recall a specific reason off the top of my head. For a more definitive answer, I'd look at the original pull request(s) to see if there was a discussion around it.</body></comment_new>
</comments>

Fixes Shell binary not getting detected correctly? #66

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Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

codecov · 2026-02-01T21:50:39Z

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✅ All modified and coverable lines are covered by tests.

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swissspidy · 2026-02-02T02:01:35Z

/gemini review

gemini-code-assist

Code Review

This pull request correctly implements the fallback to the SHELL environment variable before using the hardcoded /bin/bash path. The changes are logical and the new test case in features/shell.feature provides good coverage for the new behavior. I have one minor suggestion in src/WP_CLI/Shell/REPL.php to make the code more concise and efficient.

gemini-code-assist · 2026-02-02T02:02:46Z

src/WP_CLI/Shell/REPL.php

 		if ( getenv( 'WP_CLI_CUSTOM_SHELL' ) ) {
 			$shell_binary = getenv( 'WP_CLI_CUSTOM_SHELL' );
+		} elseif ( getenv( 'SHELL' ) ) {
+			$shell_binary = getenv( 'SHELL' );
 		} else {
 			$shell_binary = '/bin/bash';
 		}


This if/elseif/else block can be simplified and made more efficient by avoiding repeated calls to getenv(). You can use the ternary operator shorthand (?:) to achieve the same logic in a single, more concise line. This avoids calling getenv() multiple times for the same variable.

$shell_binary = getenv( 'WP_CLI_CUSTOM_SHELL' ) ?: getenv( 'SHELL' ) ?: '/bin/bash';

Copilot

Pull request overview

Adjusts wp shell’s shell binary selection to work on systems where bash isn’t located at /bin/bash (e.g. NixOS), by considering environment variables before falling back.

Changes:

Update REPL shell selection to prefer WP_CLI_CUSTOM_SHELL, then SHELL, then /bin/bash.
Add a Behat scenario intended to verify SHELL is respected.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
`src/WP_CLI/Shell/REPL.php`	Changes shell binary detection order to include `$SHELL` before `/bin/bash`.
`features/shell.feature`	Adds a feature scenario covering `$SHELL` behavior and invalid `$SHELL` erroring.

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Copilot · 2026-02-02T02:07:42Z

src/WP_CLI/Shell/REPL.php

 		if ( getenv( 'WP_CLI_CUSTOM_SHELL' ) ) {
 			$shell_binary = getenv( 'WP_CLI_CUSTOM_SHELL' );
+		} elseif ( getenv( 'SHELL' ) ) {
+			$shell_binary = getenv( 'SHELL' );
 		} else {
 			$shell_binary = '/bin/bash';


Using the SHELL environment variable as the default shell can break wp shell for users whose login shell is not bash (e.g. zsh/fish). create_prompt_cmd() builds a bash-specific command (history -r/-s/-w, read -re), so selecting a non-bash SHELL will pass the is_file/is_readable check but then fail at runtime. Consider preferring a known bash binary first (e.g. /bin/bash when it exists), and only falling back to SHELL when /bin/bash is unavailable or when SHELL points to a bash binary (e.g. basename is bash), or probe for bash on PATH.

Copilot · 2026-02-02T02:07:43Z

features/shell.feature

+  Scenario: Use SHELL environment variable as fallback
+    Given a WP install
+
+    And a session file:
+      """
+      return true;
+      """
+
+    When I try `SHELL=/bin/bash wp shell --basic < session`
+    Then STDOUT should contain:
+      """
+      bool(true)
+      """
+    And STDERR should be empty


This scenario doesn't clearly validate the new behavior of preferring $SHELL, because setting SHELL=/bin/bash matches the existing hardcoded fallback and would succeed even without the code change. Consider asserting a bash path that differs from /bin/bash (e.g. via a resolved bash path) or otherwise structuring the test so it fails on the old behavior but passes on the new one.

Copilot · 2026-02-02T02:07:43Z

features/shell.feature

+    Then STDOUT should be empty
+    And STDERR should contain:
+      """
+      Error: The shell binary '/nonsense/path' is not valid.
+      """


With the new precedence order, an invalid SHELL now causes wp shell to error even if /bin/bash is present and usable (previous behavior would have ignored SHELL and worked). The second half of this scenario locks in that behavior; please confirm this breaking change is intended. If not intended, adjust the selection logic to fall back to /bin/bash when SHELL is unset/invalid/non-bash, and update the test accordingly.

Suggested change

Then STDOUT should be empty

And STDERR should contain:

"""

Error: The shell binary '/nonsense/path' is not valid.

"""

Then STDOUT should contain:

"""

bool(true)

"""

And STDERR should be empty

Initial plan

adf5653

Copilot AI assigned Copilot and swissspidy Feb 1, 2026

Copilot started work on behalf of swissspidy February 1, 2026 19:30 View session

Use SHELL environment variable as fallback before /bin/bash

2071c56

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix shell binary detection for wp shell command~~ Use SHELL environment variable before falling back to /bin/bash Feb 1, 2026

Copilot AI requested a review from swissspidy February 1, 2026 19:35

Copilot finished work on behalf of swissspidy February 1, 2026 19:35

swissspidy added this to the 2.0.17 milestone Feb 2, 2026

swissspidy requested a review from Copilot February 2, 2026 02:01

Copilot started reviewing on behalf of swissspidy February 2, 2026 02:02 View session

gemini-code-assist bot reviewed Feb 2, 2026

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github-actions bot added command:shell scope:distribution state:unconfirmed labels Feb 2, 2026

Copilot AI reviewed Feb 2, 2026

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Use SHELL environment variable before falling back to /bin/bash #81

Use SHELL environment variable before falling back to /bin/bash #81

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Copilot AI commented Feb 1, 2026 •

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