🔧 slsp (Offset-Safe String Patcher)

slsp is a lightweight, dependency-free command-line utility for quick and precise string replacement in files.

Its primary feature is that it's offset-safe: it enforces that the replacement string is the exact same byte length as the search string. This preserves all file offsets, making it 100% safe for patching binaries, executables, and other offset-sensitive files where changing the file size would cause corruption.

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✨ Key Features

• 🔒 Offset Preservation: slsp guarantees file integrity by requiring the search and replace strings to be the exact same length.
• 🧬 Binary Safe: Works directly on bytes, making it safe for executables and text files alike.
• ⚙️ Scope Control: Use the -l flag to limit patching to only the first $N$ bytes of a file (perfect for header manipulation).
• 🔢 Occurrence Limiting: Use the -n flag to control the maximum number of replacements performed.

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🚀 Installation

Requires Go 1.23+

go install github.com/g-vvv/slsp/cmd/slsp@latest

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⌨️ Usage

Syntax

slsp -s <search> -r <replace> [-l <bytes>] [-n <count>] <filename>

Important: The byte length of the string for -s must equal the byte length of the string for -r. The tool will exit with an error if they do not match.

Flags

Flag	Description	Default
-s	(Required) The string to search for.	N/A
-r	(Required) The string to replace with.	N/A
-l	Optional: Limit patching to the first $L$ bytes.	-1 (Full file)
-n	Optional: Max number of patches to perform.	-1 (All occurrences)

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💡 Examples

1. Basic Replacement (Length-Matched)

Replace all instances of ver_01 with ver_02 in config.ini.

# "ver_01" and "ver_02" are both 6 bytes
slsp -s "ver_01" -r "ver_02" config.ini

2. Patching a Binary Header

Replace the first occurrence of LAME_MAGIC with GOOD_MAGIC within the first 1024 bytes of an executable.

# "LAME_MAGIC" and "GOOD_MAGIC" are both 10 bytes
slsp -s "LAME_MAGIC" -r "GOOD_MAGIC" -l 1024 -n 1 program.exe

3. Limiting Total Replacements

Update only the first 5 instances of DEBUG=1 to DEBUG=0 in a large log file.

slsp -s "DEBUG=1" -r "DEBUG=0" -n 5 massive.log

4. Invalid (Failed) Example

The following command will fail because the string lengths do not match:

# "Error" (5 bytes) vs "Warn" (4 bytes)
slsp -s "Error" -r "Warn" app.log

# Error: -s (search) and -r (replace/patch) strings must be the same length.

Contributors

After changes and patches, please git tag the versions and notify proxy.golang.org for version changes.

Example for v1.0.0:

git tag v1.0.0
git push origin v1.0.0
go list -m github.com/g-vvv/slsp@v1.0.0