sed

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sed (stream editor) reads text line by line, runs editing commands on it, and prints the result. With -i it writes the result back into the file. It is the standard tool to change config files in scripts and automation.

The most used command is substitute: s/OLD/NEW/FLAGS. Commands can be limited to line numbers (5, 5,10, $ = last line) or to lines that match a pattern (/regex/).

طريقة الكتابة

sed [OPTION]... 'SCRIPT' [FILE...]
sed [OPTION]... -e SCRIPT -e SCRIPT [FILE...]
sed [OPTION]... -f SCRIPT-FILE [FILE...]

الخيارات 35

الأكثر استخدامًا

-i[<suffix>], --in-place[=<suffix>]: Edit the file itself. With a suffix (like -i.bak) keep a backup.
-n, --quiet, --silent: Do not print every line; print only with the p command.
-e script, --expression=script: Add a script (use it several times for several commands).
-E, -r, --regexp-extended: Use extended regular expressions (+ ? {} | () without backslashes).
-f file, --file=file: Read the sed commands from a file.
-s, --separate: Treat several files as separate files (not one stream).
-z, --null-data: Lines end with NUL.
-u, --unbuffered: Flush output often (for live pipes).
-l n, --line-length=n: Line wrap length for the l command.
--follow-symlinks: With -i: edit the file that a link points to.
--posix: Turn off GNU extensions.
--sandbox: Do not allow the e, r and w commands.
--debug: Show how sed runs the script.
--help: Show help.
--version: Show the version.

Commands inside the script

s/old/new/: Replace the first match in each line.
s/old/new/g: Replace all matches in each line.
s/old/new/I: Replace, ignoring case (GNU).
s/old/new/2: Replace only the 2nd match.
d: Delete the line.
p: Print the line (with -n).
a text: Append a line after.
i text: Insert a line before.
c text: Change (replace) the whole line.
y/abc/xyz/: Change characters one by one (like tr).
=: Print the line number.
q: Quit.
r file: Read a file in after the line.
w file: Write the line to a file.

Addresses

5: Line 5.
5, 10: Lines 5 to 10.
$: The last line.
/regex/: Lines that match.
/start/, /end/: From a line that matches start to a line that matches end.
addr!: All lines that do NOT match the address.

أمثلة 13

$ مستخدم عادي# بصلاحية root (أو مع sudo)

1Replace text in the output
```
$sed 's/http:/https:/g' links.txt
```
The file does not change; only the output.
2Change a config file in place, with a backup
```
#sed -i.bak 's/^SELINUX=enforcing/SELINUX=permissive/' /etc/selinux/config
```
The old file is kept as config.bak.
3Turn off root login over SSH
```
#sed -i 's/^#\?PermitRootLogin .*/PermitRootLogin no/' /etc/ssh/sshd_config
```
Works if the line is commented out or not. Then systemctl reload sshd.
4Print only some lines
```
$sed -n '10,20p' /etc/services
```
Lines 10 to 20.
5Delete comments and empty lines
```
$sed '/^\s*#/d; /^\s*$/d' /etc/chrony.conf
```
Shows only the active settings.
6Add a line after a match
```
#sed -i '/^\[main\]/a gpgcheck=1' /etc/dnf/dnf.conf
```
Inserts a line under the [main] section.
7Comment out a line
```
#sed -i 's/^pool /#pool /' /etc/chrony.conf
```
Puts # before every line that starts with "pool ".
8Use another separator when the text has slashes
```
$sed 's|/var/www/html|/srv/web|g' site.conf
```
| instead of / keeps it readable.

9Use groups to reorder text

$echo "2026-10-25" | sed -E 's/([0-9]+)-([0-9]+)-([0-9]+)/\3.\2.\1/'
25.10.2026

\1 \2 \3 are the parts in brackets.

10Print the line numbers of matches
```
$sed -n '/Listen/=' /etc/httpd/conf/httpd.conf
```
Like grep -n, only the numbers.
11Delete a line by number
```
$sed -i '3d' ~/.ssh/known_hosts
```
Removes an old host key (line 3), after "REMOTE HOST IDENTIFICATION HAS CHANGED".
12Replace a value in many files
```
$sed -i 's/old-db.example.com/new-db.example.com/g' /etc/myapp/*.conf
```
Check first with grep -l old-db /etc/myapp/*.conf.
13Mask passwords in a log before you share it
```
$sed -E 's/(password=)[^& ]+/\1*****/g' app.log > app-masked.log
```
Never send real secrets in a support ticket.

انتبه

Test without -i first. Then use -i.bak so you can go back.
sed -i replaces the file with a new one (new inode): links and some permissions (and SELinux labels) can change. Check with ls -lZ on system files.
In basic regex, + ? ( ) { } | need a backslash; use -E to avoid that.

نصائح للحفظ

s/a/b/g replace all, -n 'Np' print line N, /x/d delete lines with x, -i.bak edit with backup.

`sed`

ماذا يفعل

طريقة الكتابة

الخيارات 35

Commands inside the script

Addresses

أمثلة 13

1Replace text in the output

2Change a config file in place, with a backup

3Turn off root login over SSH

4Print only some lines

5Delete comments and empty lines

6Add a line after a match

7Comment out a line

8Use another separator when the text has slashes

9Use groups to reorder text

10Print the line numbers of matches

11Delete a line by number

12Replace a value in many files

13Mask passwords in a log before you share it

انتبه

نصائح للحفظ

الدليل الكامل

ماذا يفعل

طريقة الكتابة

الخيارات 35

Commands inside the script

Addresses

أمثلة 13

1Replace text in the output

2Change a config file in place, with a backup

3Turn off root login over SSH

4Print only some lines

5Delete comments and empty lines

6Add a line after a match

7Comment out a line

8Use another separator when the text has slashes

9Use groups to reorder text

10Print the line numbers of matches

11Delete a line by number

12Replace a value in many files

13Mask passwords in a log before you share it

انتبه

نصائح للحفظ

أوامر مرتبطة

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الدليل الكامل

`sed`