Repository: dbcli/litecli (language: python)

Issue:
support for pipes with .once
Hey, thanks for this project!

When I use the official sqlite3 CLI I use `.once`'s pipe support quite a bit:

https://sqlite.org/cli.html#writing_results_to_a_file

This means I can do something like:

```
.mode markdown
.once | pbcopy
select foo from bar;
```

Then end up with the output in markdown in my clipboard (on macOS), ready to paste somewhere (like GitHub).

I discovered litecli's `.once` doesn't support this, so I ended up with a file named `| pbcopy`.

Supporting pipes like this in litecli would be a nice addition.


Discussion / hints:
>  I ended up with a file named `| pbcopy`

I'm so sorry. 😂 

Reminds me of the time I tricked my friend into deleting his home folder by doing `touch ?` and `touch ??` and `touch ???` and he decided to delete the files by calling `rm -f ?*`. We ~were~ are a bunch of clowns. 

Back to your request. This is possible (and probably easy). We have this in [mycli](https://github.com/dbcli/mycli/blob/main/mycli/packages/special/iocommands.py#L416). If you are feeling generous you can take a crack at a PR for litecli. 

Fix patch:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 58f8192..8eccd2b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,13 @@
+## Upcoming - TBD
+
+### Features
+
+* Add `\pipe_once` / `\|` commands for sending output to a command
+
+### Bug Fixes
+
+### Internal Changes
+
 ## 1.12.4 - 2024-11-11
 
 ### Bug Fixes
diff --git a/litecli/main.py b/litecli/main.py
index d1d3713..e3e6cc7 100644
--- a/litecli/main.py
+++ b/litecli/main.py
@@ -472,6 +472,7 @@ def one_iteration(text=None):
                     result_count += 1
                     mutating = mutating or is_mutating(status)
                 special.unset_once_if_written()
+                special.unset_pipe_once_if_written()
             except EOFError as e:
                 raise e
             except KeyboardInterrupt:
@@ -658,6 +659,7 @@ def output(self, output, status=None):
                 self.log_output(line)
                 special.write_tee(line)
                 special.write_once(line)
+                special.write_pipe_once(line)
 
                 if fits or output_via_pager:
                     # buffering
diff --git a/litecli/packages/special/iocommands.py b/litecli/packages/special/iocommands.py
index 78f8707..eeba814 100644
--- a/litecli/packages/special/iocommands.py
+++ b/litecli/packages/special/iocommands.py
@@ -21,7 +21,10 @@
 use_expanded_output = False
 PAGER_ENABLED = True
 tee_file = None
-once_file = once_file_args = written_to_once_file = None
+once_file = None
+written_to_once_file = None
+pipe_once_process = None
+written_to_pipe_once_process = False
 favoritequeries = FavoriteQueries(ConfigObj())
 
 
@@ -376,9 +379,12 @@ def write_tee(output):
     aliases=("\\o", "\\once"),
 )
 def set_once(arg, **_):
-    global once_file_args
-
-    once_file_args = parseargfile(arg)
+    global once_file, written_to_once_file
+    try:
+        once_file = open(**parseargfile(arg))
+    except (IOError, OSError) as e:
+        raise OSError("Cannot write to file '{}': {}".format(e.filename, e.strerror))
+    written_to_once_file = False
 
     return [(None, None, None, "")]
 
@@ -386,26 +392,66 @@ def set_once(arg, **_):
 @export
 def write_once(output):
     global once_file, written_to_once_file
-    if output and once_file_args:
-        if once_file is None:
-            try:
-                once_file = open(**once_file_args)
-            except (IOError, OSError) as e:
-                once_file = None
-                raise OSError("Cannot write to file '{}': {}".format(e.filename, e.strerror))
-
+    if output and once_file:
         click.echo(output, file=once_file, nl=False)
         click.echo("\n", file=once_file, nl=False)
+        once_file.flush()
         written_to_once_file = True
 
 
 @export
 def unset_once_if_written():
     """Unset the once file, if it has been written to."""
-    global once_file, once_file_args, written_to_once_file
+    global once_file, written_to_once_file
     if once_file and written_to_once_file:
         once_file.close()
-        once_file = once_file_args = written_to_once_file = None
+        once_file = written_to_once_file = None
+
+
+@special_command("\\pipe_once", "\\| command", "Send next result to a subprocess.", aliases=("\\|",))
+def set_pipe_once(arg, **_):
+    global pipe_once_process, written_to_pipe_once_process
+    pipe_once_cmd = shlex.split(arg)
+    if len(pipe_once_cmd) == 0:
+        raise OSError("pipe_once requires a command")
+    written_to_pipe_once_process = False
+    pipe_once_process = subprocess.Popen(
+        pipe_once_cmd,
+        stdin=subprocess.PIPE,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        bufsize=1,
+        encoding="UTF-8",
+        universal_newlines=True,
+    )
+    return [(None, None, None, "")]
+
+
+@export
+def write_pipe_once(output):
+    global pipe_once_process, written_to_pipe_once_process
+    if output and pipe_once_process:
+        try:
+            click.echo(output, file=pipe_once_process.stdin, nl=False)
+            click.echo("\n", file=pipe_once_process.stdin, nl=False)
+        except (IOError, OSError) as e:
+            pipe_once_process.terminate()
+            raise OSError("Failed writing to pipe_once subprocess: {}".format(e.strerror))
+        written_to_pipe_once_process = True
+
+
+@export
+def unset_pipe_once_if_written():
+    """Unset the pipe_once cmd, if it has been written to."""
+    global pipe_once_process, written_to_pipe_once_process
+    if written_to_pipe_once_process:
+        (stdout_data, stderr_data) = pipe_once_process.communicate()
+        if len(stdout_data) > 0:
+            print(stdout_data.rstrip("\n"))
+        if len(stderr_data) > 0:
+            print(stderr_data.rstrip("\n"))
+        pipe_once_process = None
+        written_to_pipe_once_process = False
 
 
 @special_command(


Test patch:
diff --git a/tests/test_special_iocommands.py b/tests/test_special_iocommands.py
new file mode 100644
index 0000000..ec60163
--- /dev/null
+++ b/tests/test_special_iocommands.py
@@ -0,0 +1,59 @@
+import os
+import tempfile
+
+import pytest
+
+import litecli.packages.special
+
+
+def test_once_command():
+    with pytest.raises(TypeError):
+        litecli.packages.special.execute(None, ".once")
+
+    with pytest.raises(OSError):
+        litecli.packages.special.execute(None, ".once /proc/access-denied")
+
+    litecli.packages.special.write_once("hello world")  # write without file set
+    # keep Windows from locking the file with delete=False
+    with tempfile.NamedTemporaryFile(delete=False) as f:
+        litecli.packages.special.execute(None, ".once " + f.name)
+        litecli.packages.special.write_once("hello world")
+        if os.name == "nt":
+            assert f.read() == b"hello world\r\n"
+        else:
+            assert f.read() == b"hello world\n"
+
+        litecli.packages.special.execute(None, ".once -o " + f.name)
+        litecli.packages.special.write_once("hello world line 1")
+        litecli.packages.special.write_once("hello world line 2")
+        f.seek(0)
+        if os.name == "nt":
+            assert f.read() == b"hello world line 1\r\nhello world line 2\r\n"
+        else:
+            assert f.read() == b"hello world line 1\nhello world line 2\n"
+    # delete=False means we should try to clean up
+    try:
+        if os.path.exists(f.name):
+            os.remove(f.name)
+    except Exception as e:
+        print(f"An error occurred while attempting to delete the file: {e}")
+
+
+def test_pipe_once_command():
+    with pytest.raises(IOError):
+        litecli.packages.special.execute(None, "\\pipe_once")
+
+    with pytest.raises(OSError):
+        litecli.packages.special.execute(None, "\\pipe_once /proc/access-denied")
+
+    if os.name == "nt":
+        litecli.packages.special.execute(None, '\\pipe_once python -c "import sys; print(len(sys.stdin.read().strip()))"')
+        litecli.packages.special.write_pipe_once("hello world")
+        litecli.packages.special.unset_pipe_once_if_written()
+    else:
+        with tempfile.NamedTemporaryFile() as f:
+            litecli.packages.special.execute(None, "\\pipe_once tee " + f.name)
+            litecli.packages.special.write_pipe_once("hello world")
+            litecli.packages.special.unset_pipe_once_if_written()
+            f.seek(0)
+            assert f.read() == b"hello world\n"