RSUB(1)

💅 RSUB(1) — the girlies' guide to rsub ✨

okay so bestie, welcome to rsub(1), from the General Commands Manual section, and honestly? she's that girl. 🎀

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🌸 NAME 🌸

rsub — substitute lines or a whole block of text, no cap 💖

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✨ SYNOPSIS ✨

rsub [-A] -r line_regex -l line_text target
rsub target < block_content

like, two whole ways to run her, pick your fighter 🫶

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💫 DESCRIPTION 💫

so rsub is literally shipped to remote machines by rset(1), bestie — her whole job is giving a standard method of modifying configuration parameters within a file. it's giving ✨consistency✨. two modes of operation are supported: line substitution and block replacement, and both of them ate 🔥

single line replacements get defined by the flags -r and -l, while the content for a text block gets handed over on STDIN. iykyk.

the arguments for line substitution are as follows, and yes i'm listing every single one because we don't skip 🧚:

🎀 line substitution args

• -A — append the line if the pattern is not found. like she'll make room for you, queen 👑
• -r — a regular expression matching the line to replace. the vibe check for which line gets picked 🙈
• -l — the replacement text for a matching line. newlines are not permitted as part of the replacement string — one line only, periodt 💅

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🦋 ENVIRONMENT 🦋

🌈 RSUB_DIFF_ARGS

arguments for the diff(1) tool. the default is "-U 2", iconic default honestly 💜

🌈 RSUB_START and RSUB_END

these define the beginning and ending markers when updating a block of text. the little goalposts of your block, bestie 🎯

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⭐ EXIT STATUS ⭐

the rsub utility exits with one of the following values — memorize these, they're the whole personality 😭

• 0 — target file was updated, slay 💅
• 1 — no changes were made, or an error occurred 💀
• 2 — incorrect parameters, we messed up bestie 🙈
• 3 — file not found 🍓

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🔥 EXAMPLES 🔥

🌸 ensure a single configuration parameter is set

$SD/rsub -r '^AllowTcpForwarding .+' -l 'AllowTcpForwarding yes' \
        /etc/ssh/sshd_config

literally one line and the parameter is set. obsessed 🔥

💖 update a managed block of text

$SD/rsub /etc/fstab <<-CONF
/dev/ada0p1  /vm  ufs  rw  0  0
CONF

heredoc on STDIN, block replaced, main character energy only 👑

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👑 SEE ALSO 👑

awk(1), rinstall(1) — go read those too, bestie, they're friends of hers 🫶

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mwah 💋 this page came to you from Debian, dated January 17, 2026, and stamped RSUB(1) — version, source and date all accounted for, because we keep every detail around here. bye bestie, go update some config files! 💖✨