grep system ‘grep’ command

Overview

The grep command searches for lines matching a regular expression in text files (or standard input). It uses the NuttX libc regular expression library (regcomp / regexec), so it supports real regular expressions including anchors (^, $) and character classes ([...]), not just fixed substring matching.

By default grep reads from stdin when no file is given, which makes it useful in NSH pipelines. When more than one file is searched (or when recursing into directories), the matching file name is prefixed to each result line.

Configuration

Enable the command with CONFIG_SYSTEM_GREP. This option depends on CONFIG_LIBC_REGEX and is disabled by default.

The following configuration options are available:

CONFIG_SYSTEM_GREP_PROGNAME

Program name for the grep command. Default: grep.

CONFIG_SYSTEM_GREP_PRIORITY

Task priority for the grep command. Default: 100.

CONFIG_SYSTEM_GREP_STACKSIZE

Stack size for the grep command. Default: DEFAULT_TASK_STACKSIZE.

Usage

grep [-invrHh] <pattern> [<file>...]

When no <file> is given, grep reads from stdin.

Options

-i

Case-insensitive match.

-n

Prefix each matching line with its 1-based line number.

-v

Invert the match: select lines that do not match.

-r

Recurse into subdirectories. When set, the file name is always prefixed to each result.

-H

Always print the file name prefix, even with a single input file.

-h

Never print the file name prefix.

Exit status

0

At least one line matched.

1

No line matched.

2

An error occurred (invalid option, unreadable file, bad regex, …).

Examples

Search stdin for lines containing error:

nsh> dmesg | grep error

Case-insensitive search with line numbers:

nsh> grep -in error /tmp/log.txt

Invert the match (print non-matching lines):

nsh> grep -v error /tmp/log.txt

Regular expression anchor – match lines starting with ERR:

nsh> grep "^ERR" /tmp/log.txt

Recurse a directory, always printing the file name:

nsh> grep -r -H TODO /data/src

Pipe usage – filter the output of another NSH command:

nsh> ps | grep work

Notes

• grep is built on the libc regex library; CONFIG_SYSTEM_GREP depends on CONFIG_LIBC_REGEX, so both must be enabled to satisfy the regcomp / regexec dependency.

• The -r option implies multi-file mode, so the file name is always prefixed regardless of -H / -h.

• Long lines are truncated at GREP_LINE_MAX (512 bytes); matching is performed on the (newline-stripped) content of each line.