Save command output to a file

When running long-running custom WP-CLI commands, or commands that will affect many records, it is recommended to save the output to a file for review.

Once the output for a natively supported WP-CLI command or a custom command is more than 100 lines of information, and potentially impacting dozens or more records in a database, having a log to audit what changes occurred, and what succeeded or failed, can be a critical step in debugging a root cause for any unexpected side effects.

Output can be written to the console using helpers like WP_CLI::line() and WP_CLI::log(), then redirected to a file.

Using tee to view and save output

A common option is to pipe (|) output to tee so that responses can be logged while also being able to view them in the terminal shell to monitor progress. By design, this will only write the STDOUT. The output from WP_CLI::warning(), WP_CLI::debug(), WP_CLI::error(), and WP_CLI::error_multi_line() all write to STDERR, which will display on the screen but will not be recorded into the log file.

To ensure that complete output from the command is logged, both STDERR and STDOUT should be redirected to the same place using 2>&1 . This will ensure that all of the output seen in the terminal shell will be recorded to the log.

Write STDOUT to a file, and show both STDOUT and STDERR in the terminal window

# Post ID 64791 does not exist, which will trigger a WP_CLI::warning().

$ wp demo 64783 64791 65384 | tee output.log
3 args provided.
1/3 Post found "New Product Hero Image" (ID 65384).
Warning: Post not found (ID 64791).
3/3 Post found "Lab Testing Samples" (ID 64783).
Success: Completed command.

$ cat output.log
3 args provided.
1/3 Post found "New Product Hero Image" (ID 65384).
3/3 Post found "Lab Testing Samples" (ID 64783).
Success: Completed command.

Write STDOUT and STDERR to a file, and show both STDOUT and STDERR in the terminal window

# Post ID 64791 does not exist, which will trigger a WP_CLI::warning().

$ wp demo 64783 64791 65384 2>&1 | tee all-output.log
3 args provided.
1/3 Post found "New Product Hero Image" (ID 65384).
Warning: Post not found (ID 64791).
3/3 Post found "Lab Testing Samples" (ID 64783).
Success: Completed command.

$ cat all-output.log
3 args provided.
1/3 Post found "New Product Hero Image" (ID 65384).
Warning: Post not found (ID 64791).
3/3 Post found "Lab Testing Samples" (ID 64783).
Success: Completed command.

Using > to only write to a log file

If an output display in the terminal is not required while the command is running, the redirection operator (>) can be used. By default, the redirection operator will write all STDOUT to the file and output the STDERR to the terminal shell.

Alternatively the STDERR and STDOUT can be combined to the same file using 2>&1 or redirect each output to its own file.

Write STDOUT to file, and show STDERR in the terminal window

# Post ID 64791 does not exist, which will trigger a WP_CLI::warning().

$ wp demo 64783 64791 65384 > output.log
Warning: Post not found (ID 64791).

$ cat output.log
3 args provided.
1/3 Post found "New Product Hero Image" (ID 65384).
3/3 Post found "Lab Testing Samples" (ID 64783).
Success: Completed command.

Write STDOUT to one file, STDERR to another file, with nothing showing in the terminal window

# Post ID 64791 does not exist, which will trigger a WP_CLI::warning().

$ wp demo 64783 64791 65384 > output.log 2>error.log

$ cat output.log
3 args provided.
1/3 Post found "New Product Hero Image" (ID 65384).
3/3 Post found "Lab Testing Samples" (ID 64783).
Success: Completed command.

$ cat error.log
Warning: Post not found (ID 64791).

Write both STDOUT and STDERR to a file, with nothing showing in the terminal window

# Post ID 64791 does not exist, which will trigger a WP_CLI::warning().

$ wp demo 64783 64791 65384 > output.log 2>&1

$ cat output.log
3 args provided.
1/3 Post found "New Product Hero Image" (ID 65384).
Warning: Post not found (ID 64791).
3/3 Post found "Lab Testing Samples" (ID 64783).
Success: Completed command.