sed Cheatsheet - Linux Text Editing Reference

sed has two pillars: the s/// substitution and the address that decides which lines it applies to, and combining them expresses "change this fragment only inside those lines". The sheet maps onto six recurring tasks — bulk-editing config values, dropping blank or comment lines, inserting before or after a line, printing only matches, writing regular expressions that mean what you intended, and flattening multi-line structures. The thing worth defending against is an unrecoverable mistake: sed -i rewrites the original with no confirmation, so run once without -i, read the output, then commit with -i.bak. The regex group hides a dialect trap — both BSD and GNU sed default to BRE, where +, ? and | must be escaped or you switch with -E. The division of labour is simple: sed rewrites content, awk reshapes structure, grep filters lines; and macOS sed -i demands a backup suffix while Linux accepts a bare -i.

SysOps·37 commands·Last updated 2026-07-21

Typical Use Case

For developers who need to rewrite configuration files in bulk. The risk in sed concentrates on irreversibility: -i edits in place with no undo, and the / delimiter collides with paths inside the pattern. This sheet is organised into six groups — substitution, deletion, insertion, printing, regular expressions and multi-line operations. Three pieces of advice matter most: use -i.bak so there is a backup, switch the delimiter to | when the pattern contains slashes, and always preview once without -i before writing to disk.

Substitute 8

sed 's/old/new/' file

Replace first match per line

sed 's/old/new/g' file

Replace all matches (global)

sed 's/old/new/2' file

Replace the 2nd match per line

sed 's/old/new/I' file

Case-insensitive match

sed -i 's/old/new/g' file

Edit the file in place

sed -i.bak 's/old/new/g' file

Edit and back up the original

sed 's/\/path\/old/path\/new/g' file

Escape slashes when replacing paths

sed 's|old|new|g' file

Use | as delimiter to avoid escaping slashes

Delete 7

sed '5d' file

Delete line 5

sed '5,10d' file

Delete lines 5-10

sed '/pattern/d' file

Delete matching lines

sed '/^$/d' file

Delete blank lines

sed '/^#/d' file

Delete comment lines

sed '$d' file

Delete the last line

sed '1d;$d' file

Delete the first and last lines

Insert & Append 5

sed '5i\new text' file

Insert before line 5

sed '5a\new text' file

Append after line 5

sed '/pattern/i\new text' file

Insert before matching lines

sed '/pattern/a\new text' file

Append after matching lines

sed '5i\line1\nline2' file

Insert multiple lines

Print 5

sed -n '5p' file

Print only line 5

sed -n '5,10p' file

Print only lines 5-10

sed -n '/pattern/p' file

Print only matching lines

sed -n '1p;$p' file

Print first and last lines

sed 's/old/new/p' file

Substitute and print changed lines

Regular Expression 7

sed 's/^prefix/new/' file

Match line start

sed 's/suffix$/new/' file

Match line end

sed 's/\<word\>/new/g' file

Match word boundary

sed 's/[0-9]/X/g' file

Match digits

sed 's/[^0-9]/X/g' file

Match non-digits

sed 's/$pattern$/\1/g' file

Capture group and backreference

sed -E 's/(old)/\1-new/g' file

Extended regex (-E or -r)

Multi-line 5

sed ':a;N;$!ba;s/\n//g' file

Delete all newlines

sed 'N;s/\n/ /'

Merge adjacent two lines

sed '/start/,/end/s/old/new/g' file

Substitute within a range

sed '/start/,/end/d' file

Delete lines within a range

sed '/start/,/end/p' file

Print lines within a range

Parameter matrix

Parameter	Effect	Example
`s///`	替换每行第一个匹配	`sed 's/old/new/' file`
`/g`	全局替换该行所有匹配	`sed 's/old/new/g' file`
`/2`	只替换每行第 2 个匹配	`sed 's/old/new/2' file`
`/I`	忽略大小写匹配	`sed 's/old/new/I' file`
`-i`	原地编辑（无备份，不可撤销）	`sed -i 's/old/new/g' file`
`-i.bak`	原地编辑并保留 .bak 备份	`sed -i.bak 's/old/new/g' file`
`自定义分隔符 \|`	模式含 / 时免转义	`sed 's\|/old/\|/new/\|g' file`
`Nd / 'N,Md'`	删除第 N 行 / 第 N 到 M 行	`sed '5,10d' file`
`/pat/d`	删除匹配模式的行	`sed '/^#/d' config`
`Ni / Na`	在第 N 行前插入 / 后追加	`sed '5a\new text' file`
`-n "Np"`	只打印指定行（不自动输出）	`sed -n '5,10p' file`
`/start/,/end/s///`	只在指定范围内替换	`sed '/start/,/end/s/old/new/g' file`
` 与 \1`	捕获组与反向引用（BRE）	`sed 's/$pattern$/\1/g' file`
`-E`	扩展正则，( ) 无需转义	`sed -E 's/(old)/\1-new/g' file`
`N;$!ba;s/\n//g`	删除所有换行符合并全文	`sed ':a;N;$!ba;s/\n//g' file`

Common pitfalls

Symptom替换含路径的字符串后 sed 报错或结果为空。

Cause分隔符 / 与模式中的路径冲突，需要大量转义。

Fix换用其它分隔符：sed "s|/old/path|/new/path|g" file。

Symptomsed -i 改完文件后内容全空了，无法恢复。

Cause模式匹配范围比预期大（如 .* 贪婪匹配整行），且 -i 没有备份。

Fix改用 -i.bak 留备份；执行前先不带 -i 看输出确认。

Symptom只想替换每行第一次出现，结果全被替换了。

Cause模式里写了 g 标志，或把 . 当成通配导致匹配多处。

Fix去掉 g；字面匹配用 . 转义成 \. 或改用 grep -F 先确认匹配数。

SymptommacOS 上 sed -i 报错或文件被清空。

CauseBSD 版 sed 的 -i 必须跟备份后缀，不能直接 -i。

FixmacOS 用 sed -i "" "s/old/new/g" file，或 sed -i.bak（会自动生成 .bak）。

Symptom反向引用 \1 输出为空或保留了原样。

CauseBRE 下捕获组必须写成 ，且替换串里写 \1。

Fix改用 -E 简化写法：sed -E "s/(old)/\1-new/g" file。

Symptom删除注释行时把含 # 的正文也删了。

Cause/^#/ 只匹配行首是 # 的行，若写成 /#/ 则会删掉所有含 # 的行。

Fix用锚定写法 sed "/^#/d"；确认后先不带 -d 的 -n 打印查看匹配范围。

Symptom在 macOS/BSD 与 GNU 之间来回切换，命令行为不一致。

Cause两者的 -i、-E 语法与部分扩展选项存在差异。

Fix统一用 -E 与 -i.bak 写法，两个平台都能工作；避免依赖 BSD 特有选项。

Troubleshooting

1改文件前先预览结果
sed 's/old/new/g' config.yaml
不带 -i 只输出；确认无误后再加 -i.bak 落盘。
2原地修改并保留备份
sed -i.bak 's/old/new/g' f.txt
生成 f.txt.bak，出问题可立即回滚。
3清理注释与空行
sed '/^#/d; /^$/d' nginx.conf
多条命令用分号分隔，一次扫描完成。
4只在指定范围内替换
sed '/start/,/end/s/old/new/g' file
范围模式 /start/,/end/ 可用于删除、替换与打印。
5macOS 上的原地编辑
sed -i '' 's/old/new/g' file
BSD 版 -i 必须带后缀，空串表示不备份；要备份用 -i.bak。

Command Examples

Dry-run a substitution, then edit in place with a backup

sed 's/localhost/0.0.0.0/g' config.yaml
sed -i.bak 's/localhost/0.0.0.0/g' config.yaml

第一行不带 -i 只输出，确认无误后第二行用 -i.bak 落盘并留下 .bak。含 / 的模式把分隔符换成 # 更省心。

Output

server: 0.0.0.0
bind: 0.0.0.0:8080
url: http://localhost/api

Substitute within a range of markers

sed '/# BEGIN/,/# END/s/old/new/g' config.ini

地址区间 /start/,/end/ 限定作用范围，避免误改区块外的同名内容。删除区间用 sed '/start/,/end/d'。

Output

managed-by-tool

Join adjacent lines

sed -n 'N;s/\n/ /;P;D' data.txt

N 把下一行读进模式空间，s 把换行换成空格。sed 的多行处理语法较绕，简单的连续行合并也可以用 paste -sd ' ' 更直观。

Output

first line second line

Common Pitfalls

sed -i has no undo and no backup; verify without -i first, then use -i.bak.
sed defaults to BRE where \+ \| and \( are not special; add -r for extended regular expressions.
A pattern containing / collides with the delimiter — switch to # or |.
A range deletion like sed '/start/,/end/d' runs to end of file when the end marker is missing.
sed is a stream editor, not a logic engine; reach for awk or a script when the transformation is conditional.

Tips

Before editing in place with sed -i, back up first (-i.bak), or preview without -i.
sed uses BRE (basic regex) by default; +, ?, | must be escaped or enable ERE with -E.
On macOS, sed -i requires a backup suffix (e.g. -i ""); on Linux -i works directly.

FAQ

What happens if I omit the g flag in a sed substitution?

Without g, sed replaces only the first match on each line. Given a line with three occurrences of old, sed 's/old/new/' changes just the first and leaves the rest untouched — you must write s/old/new/g to replace them all. That restraint is occasionally useful, for example when you only want to rewrite the first port number in a URL.

How do I operate on a range of lines with sed?

Use Np or a range: sed -n '5,10p' file prints lines 5 through 10, and sed '5,10d' file deletes them. The pattern form sed '/start/,/end/d' file removes everything between the line matching start and the line matching end. Pattern-based ranges are more robust than line numbers for files with irregular structure.

What do the s, d, i and a commands do in sed?

s substitutes matched text in place. d deletes the whole line. i inserts before a matching line, and a appends after it. The key difference is that s keeps the line and changes content, d discards it entirely, and i/a increase the line count. They combine with semicolons: sed '/^#/d; /^$/d' nginx.conf strips comment lines and blank lines in one pass.

Can sed work across lines?

Yes, though the syntax takes a moment. N appends the next line to the pattern space, so N followed by s/\n/ / merges two lines into one; the inverse, sed ':a;N;$!ba;s/\n//g' file, strips every newline and collapses the file to a single line. GNU sed also has -z so N splits on NUL instead of newline, which helps for compressed blobs that contain no newlines.

Why does my sed regex sometimes not take effect?

Most often it is delimiter collision: if the script uses / and your pattern also contains /, as URLs do, you must switch delimiters, e.g. s#https://x#http://y#. Also remember sed defaults to BRE, where \+ \| and \( are not special — write BRE syntax or add -r to switch to extended regular expressions.

Official References

Each command links to its official documentation below, so you can verify the latest usage and read deeper.

Linux man-pages

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Publicly updated on Jul 21, 2026, continuously proofread against official docs.

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Typical Use Case

Substitute 8

Delete 7

Insert & Append 5

Print 5

Regular Expression 7

Multi-line 5

Parameter matrix

Common pitfalls

Troubleshooting

Command Examples

Dry-run a substitution, then edit in place with a backup

Substitute within a range of markers

Join adjacent lines

Common Pitfalls

Tips

FAQ

Related Cheatsheets

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Official References

Maintained by LaoHand

Contact Us