walk and sor, a combined replacement for find

8 files changed, 483 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
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--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,8 @@
+# Editor backup files
+*~
+\#*
+.\#*
+.*.swp
+
+# Build artifacts
+walk
\ No newline at end of file
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
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diff --git a/Makefile b/Makefile
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--- /dev/null
+++ b/Makefile
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+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+CFLAGS = -Wall -O2
+
+.DEFAULT_GOAL := walk
+
+.PHONY: clean
+clean:
+	$(RM) walk
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
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+`walk` and `sor`
+================
+
+This repository contains `walk` and `sor`, two utility programs that
+collectively replace [`find`][find]. `walk` recursively walks the directories
+specified on the command line (or the current directory, if none is specified),
+printing each file path. `sor` (“shell or”) reads file paths from standard
+input; for each path, it evaluates its arguments as Bash snippets, passing the
+path as an argument to each and printing the path if any snippet exits with
+status 0. For example, instead of saying
+
+    find . -type f -name \*foo\*
+
+you can say
+
+    walk | grep foo | sor 'test -f'
+
+[find]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html
+
+
+Performance
+-----------
+
+By avoiding syscalls, `walk` achieves substantially better performance than
+`find`. A microbenchmark –
+
+    $ time find /usr >/dev/null
+    
+    real    0m3.542s
+    user    0m0.880s
+    sys     0m2.646s
+    $ time walk /usr >/dev/null
+    
+    real    0m2.311s
+    user    0m0.370s
+    sys     0m1.926s
+
+– shows `walk` executing nearly 40% faster on a local file system with a hot
+cache. Performance on network file systems should be even better. On the other
+hand, `find` implements its predicates in-process, making them orders of
+magnitude faster than `sor`:
+
+    $ time find /usr -type f >/dev/null
+    
+    real    0m3.464s
+    user    0m0.831s
+    sys     0m2.615s
+    $ time walk /usr | sor 'test -f' >/dev/null
+    
+    real    7m40.127s
+    user    1m47.818s
+    sys     2m48.595s
+
+
+History
+-------
+
+`walk` and `sor` were originally written for [Plan 9 from Bell Labs][] by
+[Dan Cross][]. The [original source][] is available.
+
+[Dan Cross]: http://pub.gajendra.net/about
+[Plan 9 from Bell Labs]: https://web.archive.org/web/20170601064029/http://plan9.bell-labs.com/plan9/index.html
+[original source]: https://web.archive.org/web/http://plan9.bell-labs.com/sources/contrib/cross/
+
+
+Disclaimer
+----------
+
+This is not an official Google product.
diff --git a/sor b/sor
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+++ b/sor
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+#!/bin/bash
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+while read file; do
+	for test in "$@"; do
+		if eval "$test \"$file\""; then
+			echo "$file"
+			continue 2
+		fi
+	done
+done
diff --git a/sor.1 b/sor.1
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+++ b/sor.1
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+.\" Copyright 2019 Google LLC
+.\"
+.\" Licensed under the Apache License, Version 2.0 (the "License");
+.\" you may not use this file except in compliance with the License.
+.\" You may obtain a copy of the License at
+.\"
+.\"     https://www.apache.org/licenses/LICENSE-2.0
+.\"
+.\" Unless required by applicable law or agreed to in writing, software
+.\" distributed under the License is distributed on an "AS IS" BASIS,
+.\" WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+.\" See the License for the specific language governing permissions and
+.\" limitations under the License.
+.TH SOR 1 2019-09-16
+.SH NAME
+sor \- combine shell predicates with logical or
+.SH SYNOPSIS
+.B sor
+.IR SNIPPET ...
+.SH DESCRIPTION
+Read paths from standard input. For each path, evaluate each argument as a
+.BR bash (1)
+snippet with the path as the first argument. Print the path to standard output
+if any of the snippets exits with status 0.
+.SH EXAMPLE
+.EX
+walk /etc | sor 'test -f'
+.EE
+.SH "SEE ALSO"
+.BR find (1),
+.BR walk (1)
diff --git a/walk.1 b/walk.1
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+++ b/walk.1
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+.\" Copyright 2019 Google LLC
+.\"
+.\" Licensed under the Apache License, Version 2.0 (the "License");
+.\" you may not use this file except in compliance with the License.
+.\" You may obtain a copy of the License at
+.\"
+.\"     https://www.apache.org/licenses/LICENSE-2.0
+.\"
+.\" Unless required by applicable law or agreed to in writing, software
+.\" distributed under the License is distributed on an "AS IS" BASIS,
+.\" WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+.\" See the License for the specific language governing permissions and
+.\" limitations under the License.
+.TH WALK 1 2019-09-16
+.SH NAME
+walk \- walk file system
+.SH SYNOPSIS
+.B walk
+.RI [\| DIRECTORY ...\]
+.SH DESCRIPTION
+Recursively list the specified
+.I DIRECTORY
+(or directories). Recursively list the current directory if no directory is
+specified.
+.SH NOTES
+.B walk
+does not traverse symlinks.
+.SH "SEE ALSO"
+.BR find (1),
+.BR sor (1)
diff --git a/walk.c b/walk.c
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--- /dev/null
+++ b/walk.c
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+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <dirent.h>
+
+static const char *const JUST_CURRENT_DIRECTORY[] = {".", NULL};
+
+// Like readdir(3), but resets errno(3) before the call to make it easy to
+// check.
+static struct dirent *readdir2(DIR *const dirp)
+{
+	errno = 0;
+	return readdir(dirp);
+}
+
+// Like realloc(3), but exits the binary in an out-of-memory situation.
+static void *realloc2(void *ptr, const size_t size)
+{
+	if (!(ptr = realloc(ptr, size))) {
+		perror("realloc");
+		exit(EXIT_FAILURE);
+	}
+	return ptr;
+}
+
+static void strcpy3(char *dest, const char *s1, const char *s2, const char *s3)
+{
+	stpcpy(stpcpy(stpcpy(dest, s1), s2), s3);
+}
+
+// Walks the directory named dirname, printing the names of all files it
+// contains (but not the name of the directory itself). Returns 2 if dirname is
+// not a directory and 1 if another error occurs.
+static int walk(const char dirname[])
+{
+	DIR *const dir = opendir(dirname);
+	if (!dir) {
+		if (errno != ENOTDIR) {
+			perror(dirname);
+			return 1;
+		}
+		return 2;
+	}
+	int r = 0;
+	char *filename = NULL;
+	for (const struct dirent *f = readdir2(dir); f; f = readdir2(dir)) {
+		if (strcmp(f->d_name, ".") == 0
+				|| strcmp(f->d_name, "..") == 0)
+			continue;
+		filename = realloc2(filename,
+			strlen(dirname) + 1 + strlen(f->d_name) + 1);
+		strcpy3(filename, dirname, "/", f->d_name);
+		// TODO(bbaren): Emulate Plan 9's cleanname(3).
+		puts(filename);
+		// Walk the file if we can successfully open it as a directory.
+		// Don't worry about it if it's not one (walk(filename) == 2).
+		if ((f->d_type == DT_DIR || f->d_type == DT_UNKNOWN)
+				&& walk(filename) == 1)
+			r = 1;
+	}
+	if (errno) {	// from readdir
+		perror(dirname);
+		r = 1;
+	}
+	free(filename);
+	if (closedir(dir)) {
+		perror(dirname);
+		r = 1;
+	}
+	return r;
+}
+
+int main(const int argc, const char *const argv[])
+{
+	int r = 0;
+	const char *const *const dirs =
+		argc == 1 ? JUST_CURRENT_DIRECTORY : argv + 1;
+	for (int i = 0; dirs[i]; ++i) {
+		puts(dirs[i]);
+		r |= walk(dirs[i]);
+	}
+	return r;
+}