wc

What it does

How to write it

wc [OPTION]... [FILE]...
wc [OPTION]... --files0-from=F

Most used

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$ run as a normal user# run as root (or with sudo)

1. 1Lines, words and bytes

   $wc /etc/passwd
     45   95 2512 /etc/passwd

   Three numbers: lines, words, bytes.

2. 2Count lines only

   $wc -l /etc/passwd
   45 /etc/passwd

   Each line is one account.

3. 3Count results of a command

   $ls /etc | wc -l

   How many entries in /etc.

4. 4Only the number, without the file name

   $wc -l < /etc/passwd
   45

   Input from a redirect has no name. Good in scripts.

5. 5Count running processes

   $ps -e --no-headers | wc -l

   How many processes run now.

6. 6Count failed SSH logins today

   #journalctl -u sshd --since today | grep -c "Failed password"

   grep -c counts directly; same as grep … | wc -l.

7. 7Count lines of all scripts in a folder

   $wc -l *.sh

   Each file plus a total line.

8. 8Check the longest line of a file

   $wc -L config.yaml

   Some tools have line length limits.

9. 9Count characters in UTF-8 text

   $echo -n "سلام" | wc -m
   4

   -c would count 8 bytes; -m counts 4 characters.

10. 10Compare the size of two lists

    $wc -l before.txt after.txt

    Quick check after a cleanup or an import.

11. 11Alert when a log grows too fast

    $[ "$(wc -l < /var/log/app/error.log)" -gt 1000 ] && echo "too many errors"

    A tiny monitoring check.

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