feat: add output file management for per-node command results

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bssh"
-version = "0.2.0"
+version = "0.3.0"
 edition = "2021"
 authors = ["Jeongkyu Shin"]
 description = "Parallel SSH command execution tool for cluster management"
@@ -22,6 +22,7 @@ indicatif = "0.18"
 rpassword = "7"
 directories = "5"
 dirs = "6.0"
+chrono = "0.4"
 
 [dev-dependencies]
 tempfile = "3"

README.md

@@ -10,6 +10,7 @@ A high-performance parallel SSH command execution tool for cluster management, b
 - **Flexible Authentication**: Support for SSH keys and SSH agent
 - **Host Key Verification**: Secure host key checking with known_hosts support
 - **Cross-Platform**: Works on Linux and macOS
+- **Output Management**: Save command outputs to files per node with detailed logging
 
 ## Installation
 
@@ -158,6 +159,52 @@ bssh -c webservers "sudo systemctl restart nginx"
 bssh -c production --output-dir ./logs "tail -n 100 /var/log/syslog"
 ```
 
+## Output File Management
+
+When using the `--output-dir` option, bssh saves command outputs to structured files:
+
+### File Structure
+```
+output-dir/
+├── hostname1_20250821_143022.stdout   # Standard output
+├── hostname1_20250821_143022.stderr   # Standard error (if any)
+├── hostname2_20250821_143022.stdout   # Per-node outputs
+├── hostname2_20250821_143022.error    # Connection/execution errors
+├── hostname3_20250821_143022.empty    # Marker for no output
+└── summary_20250821_143022.txt        # Overall execution summary
+```
+
+### File Types
+- **`.stdout`**: Contains standard output from successful commands
+- **`.stderr`**: Contains standard error output (created only if stderr is not empty)
+- **`.error`**: Contains error messages for failed connections or executions
+- **`.empty`**: Marker file when command produces no output
+- **`summary_*.txt`**: Overall execution summary with success/failure counts
+
+### File Headers
+Each output file includes metadata headers:
+```
+# Command: df -h
+# Host: server1.example.com
+# User: admin
+# Exit Status: 0
+# Timestamp: 20250821_143022
+
+[actual command output follows]
+```
+
+### Example Usage
+```bash
+# Save outputs to timestamped directory
+bssh -c production --output-dir ./results/$(date +%Y%m%d) "ps aux | head -10"
+
+# Collect system information
+bssh -c all-servers --output-dir ./system-info "uname -a; df -h; free -m"
+
+# Debug failed services
+bssh -c webservers --output-dir ./debug "systemctl status nginx"
+```
+
 ## Development
 
 ### Building

docs/man/bssh.1

@@ -1,6 +1,6 @@
 .\" Manpage for bssh
 .\" Contact the maintainers to correct errors or typos.
-.TH BSSH 1 "August 21, 2025" "v0.2.0" "bssh Manual"
+.TH BSSH 1 "August 21, 2025" "v0.3.0" "bssh Manual"
 
 .SH NAME
 bssh \- Backend.AI SSH - Parallel command execution across cluster nodes
@@ -50,7 +50,8 @@ Maximum parallel connections (default: 10)
 
 .TP
 .BR \-\-output\-dir " " \fIOUTPUT_DIR\fR
-Output directory for command results
+Output directory for command results. When specified, saves command outputs
+to separate files for each node with stdout, stderr, and execution summary
 
 .TP
 .BR \-v ", " \-\-verbose
@@ -180,6 +181,17 @@ Use SSH agent for authentication:
 .TP
 Save output to files:
 .B bssh --output-dir ./results -c production "ps aux"
+.RS
+Creates timestamped files per node:
+.br
+- hostname_TIMESTAMP.stdout (standard output)
+.br
+- hostname_TIMESTAMP.stderr (error output)
+.br  
+- hostname_TIMESTAMP.error (connection errors)
+.br
+- summary_TIMESTAMP.txt (execution summary)
+.RE
 
 .SH EXIT STATUS
 .TP
@@ -190,6 +202,33 @@ Success - all commands executed successfully on all nodes
 .B 1
 Failure - one or more commands failed or connection errors occurred
 
+.SH OUTPUT FILES
+When using the
+.B --output-dir
+option, bssh creates the following files:
+
+.TP
+.I hostname_YYYYMMDD_HHMMSS.stdout
+Standard output from successful command execution
+
+.TP
+.I hostname_YYYYMMDD_HHMMSS.stderr
+Standard error output (created only if stderr is not empty)
+
+.TP
+.I hostname_YYYYMMDD_HHMMSS.error
+Error messages for failed connections or command execution
+
+.TP
+.I hostname_YYYYMMDD_HHMMSS.empty
+Marker file when command produces no output
+
+.TP
+.I summary_YYYYMMDD_HHMMSS.txt
+Overall execution summary with success/failure counts for all nodes
+
+Each output file includes metadata headers with command, host, user, exit status, and timestamp information.
+
 .SH FILES
 .TP
 .I ~/.bssh/config.yaml