cat, tac

هذا الجزء لم يُترجم بعد. أنت ترى النص الإنجليزي.

ماذا يفعل

cat (concatenate) writes the content of one or more files to standard output. With one file you read it; with several files you join them; with a redirect you create a new file.

It is perfect for short files. For long files, use less (scrolling) or head/tail (parts).

tac does the same, but starts with the last line (useful for logs: newest first).

طريقة الكتابة

cat [OPTION]... [FILE]...
tac [OPTION]... [FILE]...

الخيارات 15

الأكثر استخدامًا

-n, --number: Number all lines.
-b, --number-nonblank: Number only non-empty lines.
-A, --show-all: Show hidden characters: tabs as ^I, line ends as $, others as ^ or M- (same as -vET).
-E, --show-ends: Show $ at the end of each line.
-T, --show-tabs: Show tabs as ^I.
-v, --show-nonprinting: Show non-printable characters with ^ and M- notation.
-e: Same as -vE.
-t: Same as -vT.
-s, --squeeze-blank: Show several empty lines as one.
-u: Ignored.
--help: Show help.
--version: Show the version.

tac

-b, --before: Put the separator before the record instead of after.
-r, --regex: Treat the separator as a regular expression.
-s, --separator=string: Use this separator instead of a new line.

أمثلة 12

$ مستخدم عادي# بصلاحية root (أو مع sudo)

1Show a short file
```
$cat /etc/hostname
server1.example.com
```
The fastest way to read a small file.
2Show line numbers
```
$cat -n /etc/fstab
```
Easy to talk about "line 7".
3Find hidden characters (tabs, Windows line ends)
```
$cat -A deploy.sh | head
#!/bin/bash^M$
```
^M$ means Windows line ends: Bash will fail. ^I would show tabs (bad in YAML).
4Join several files into one
```
$cat part1.csv part2.csv part3.csv > all.csv
```
The files are added one after the other.
5Create a file with several lines (here-document)
```
$cat > /tmp/test.conf <<'EOF'
port=8080
log=/var/log/app.log
EOF
```
Everything until the line EOF goes into the file.

6Add lines to a root-owned file

$cat <<'EOF' | sudo tee -a /etc/hosts
192.168.122.20 server2.example.com server2
EOF

sudo tee -a appends as root.

7Show the newest log lines first
```
#tac /var/log/dnf.log | head -20
```
The last 20 events, newest at the top.
8Show the OS version
```
$cat /etc/os-release
```
NAME, VERSION_ID and ID of the distribution.
9Squeeze empty lines while reading
```
$cat -s notes.txt
```
Several empty lines become one.
10Read kernel information
```
$cat /proc/cpuinfo | grep "model name" | head -1
```
/proc files are created by the kernel when you read them.
11Show a file only if it exists
```
$[ -f /etc/motd ] && cat /etc/motd
```
No error message in a script when the file is missing.
12Copy a disk image to a USB stick (as a simple dd)
```
#cat rhel-10.iso > /dev/sdX
```
Works like dd for this job. Check the device name three times: it overwrites the whole disk.

انتبه

cat bigfile floods the screen; use less.
cat file > file empties the file before reading it. Never read and write the same file in one command.
"Useless use of cat": cat file | grep x works, but grep x file is simpler.

نصائح للحفظ

cat = show/join, tac = backwards, cat -A = invisible characters, cat > file <<'EOF' = new file.

`cat, tac`

ماذا يفعل

طريقة الكتابة

الخيارات 15

tac

أمثلة 12

1Show a short file

2Show line numbers

3Find hidden characters (tabs, Windows line ends)

4Join several files into one

5Create a file with several lines (here-document)

6Add lines to a root-owned file

7Show the newest log lines first

8Show the OS version

9Squeeze empty lines while reading

10Read kernel information

11Show a file only if it exists

12Copy a disk image to a USB stick (as a simple dd)

انتبه

نصائح للحفظ

الدليل الكامل

ماذا يفعل

طريقة الكتابة

الخيارات 15

tac

أمثلة 12

1Show a short file

2Show line numbers

3Find hidden characters (tabs, Windows line ends)

4Join several files into one

5Create a file with several lines (here-document)

6Add lines to a root-owned file

7Show the newest log lines first

8Show the OS version

9Squeeze empty lines while reading

10Read kernel information

11Show a file only if it exists

12Copy a disk image to a USB stick (as a simple dd)

انتبه

نصائح للحفظ

أوامر مرتبطة

مُستخدم في هذه الدروس

مُستخدم في هذه المعامل

الدليل الكامل

`cat, tac`