View & Inspect Files

Read logs without opening a full editor
Confirm file type before editing
Watch a log grow (tail -f)

Must-know cold

less FILE · head -n 20 · tail -n 50 · tail -f LOG
cat FILE (small files only) · wc -l FILE
file PATH · stat PATH · ls -l PATH

Commands

`cat`

Definition: Concatenate and print file contents to stdout (best for small files).

Option	Argument	Meaning	Example
(none)	`FILE...`	Concatenate/print file(s) to stdout	`cat f.txt`
`-n`	`FILE`	Number all lines	`cat -n f.txt`
`-b`	`FILE`	Number non-blank lines	`cat -b f.txt`
`-A`	`FILE`	Show non-printing (`^I` tab, `$` end)	`cat -A f.txt`
`-s`	`FILE`	Squeeze repeated blank lines	`cat -s f.txt`
`-v`	`FILE`	Show non-printing (except tab/NL)	`cat -v f.txt`

Flag combos

Combo	Meaning	Example
`cat -n file \| head`	Numbered preview	`cat -n app.log \| head`
`cat a b > c`	Concatenate into new file	`cat part1 part2 > all`

`less`

Definition: Page through a file interactively (scroll, search, follow).

Option	Argument	Meaning	Example
(none)	`FILE`	Interactive pager (scroll/search)	`less /var/log/syslog`
`-N`	`FILE`	Show line numbers	`less -N file`
`-S`	`FILE`	Chop long lines (no wrap)	`less -S wide.log`
`-i`	`FILE`	Search ignore case	`less -i file` then `/error`
`-F`	`FILE`	Quit if one screen	`less -F short`
`-R`	`FILE`	Raw ANSI colors	`less -R colored.log`
`+F`	`FILE`	Start in follow mode (like tail -f)	`less +F app.log`
`+/PAT`	`FILE`	Open at first match	`less +/ERROR app.log`

Inside less (keys):

q quit · /pat search · n next · g top · G end · F follow · Ctrl-C stop follow

Flag combos

Combo	Meaning	Example
`less -NS file`	Numbers + chop	`less -NS access.log`

`head`

Definition: Show the first lines (or bytes) of a file.

Option	Argument	Meaning	Example
(none)	`FILE`	First 10 lines (default)	`head file`
`-n`	`N FILE`	First N lines	`head -n 20 file`
`-n`	`-N FILE`	All but last N lines (GNU)	`head -n -5 file`
`-c`	`N FILE`	First N bytes	`head -c 100 file`
`-q`	`FILE...`	Never print filename headers	`head -q *.log`
`-v`	`FILE`	Always print headers	`head -v a b`

Flag combos

Combo	Meaning	Example
`head -n 5`	Quick sample	`head -n 5 /etc/passwd`

`tail`

Definition: Show the last lines of a file; with -f, follow live appends.

Option	Argument	Meaning	Example
(none)	`FILE`	Last 10 lines	`tail file`
`-n`	`N FILE`	Last N lines	`tail -n 50 app.log`
`-n`	`+N FILE`	From line N to end	`tail -n +100 file`
`-c`	`N FILE`	Last N bytes	`tail -c 200 file`
`-f`	`FILE`	Follow append (live log)	`tail -f app.log`
`-F`	`FILE`	Follow by name; retry if rotated	`tail -F /var/log/app.log`
`--pid`	`PID`	With `-f`: stop when PID dies	`tail -f log --pid=1234`
`-q`	`FILE...`	No headers	`tail -q *.log`

Flag combos

Combo	Meaning	Example
`tail -n 100 -f log`	Last 100 then follow	`tail -n100 -f app.log`
`tail -F log`	Survive logrotate	Production agents

`wc`

Definition: Count lines, words, and/or bytes in input.

Option	Argument	Meaning	Example
(none)	`FILE`	Lines, words, bytes	`wc file`
`-l`	`FILE`	Line count only	`wc -l app.log`
`-w`	`FILE`	Word count	`wc -w file`
`-c`	`FILE`	Byte count	`wc -c file`
`-m`	`FILE`	Character count	`wc -m file`
`-L`	`FILE`	Length of longest line (GNU)	`wc -L file`

Flag combos

Combo	Meaning	Example
`grep ERR log \| wc -l`	Count matches	`grep -c` also works

`file`

Definition: Guess a file’s type from content (magic), not just the name.

Option	Argument	Meaning	Example
(none)	`PATH`	Guess type from content/magic	`file /bin/ls`
`-b`	`PATH`	Brief; no filename prefix	`file -b x`
`-i`	`PATH`	MIME type	`file -i doc`
`-L`	`PATH`	Follow symlinks	`file -L link`
`-s`	`PATH`	Read special files (block/char)	`file -s /dev/sda`
`-z`	`PATH`	Look inside compressed	`file -z a.gz`

Flag combos

Combo	Meaning	Example
`file *`	Type all in dir	Quick triage

`stat`

Definition: Show detailed inode metadata: size, mode, owner, timestamps.

Option	Argument	Meaning	Example
(none)	`PATH`	Size, mode, uid/gid, timestamps, inode	`stat file`
`-c`	`FORMAT PATH`	Custom format (GNU)	`stat -c '%n %s %a' f`
`-f`	`PATH`	Filesystem status (like df)	`stat -f /`
`-L`	`PATH`	Follow symlink	`stat -L link`
`-t`	`PATH`	Terse one line	`stat -t file`

Useful `-c` formats:

%n name · %s size · %a octal mode · %A human mode · %U/%G owner · %y mtime

Flag combos

Combo	Meaning	Example
`stat -c '%a %n' f`	Octal mode + name	Permission checks
`stat -c '%y %n' f`	Mtime

Common recipes

Goal	Command
Sample start of log	`head -n 20 app.log`
Sample end of log	`tail -n 50 app.log`
Live follow	`tail -f app.log`
Page a large file	`less app.log`
Line count	`wc -l app.log`
Is it binary?	`file ./artifact`
Mode + owner + size	`stat file` or `ls -l file`

Pitfalls

cat huge logs floods the terminal — prefer less / tail.
tail -f follows the inode; after rotate use tail -F.
file is a guess — not security proof.
Binary files: less may warn; don’t cat binaries into an SSH session.

For more details, try man <command> in your terminal.

View & Inspect Files

Read logs without opening a full editor
Confirm file type before editing
Watch a log grow (tail -f)

Must-know cold

less FILE · head -n 20 · tail -n 50 · tail -f LOG
cat FILE (small files only) · wc -l FILE
file PATH · stat PATH · ls -l PATH

Commands

`cat`

Definition: Concatenate and print file contents to stdout (best for small files).

Option	Argument	Meaning	Example
(none)	`FILE...`	Concatenate/print file(s) to stdout	`cat f.txt`
`-n`	`FILE`	Number all lines	`cat -n f.txt`
`-b`	`FILE`	Number non-blank lines	`cat -b f.txt`
`-A`	`FILE`	Show non-printing (`^I` tab, `$` end)	`cat -A f.txt`
`-s`	`FILE`	Squeeze repeated blank lines	`cat -s f.txt`
`-v`	`FILE`	Show non-printing (except tab/NL)	`cat -v f.txt`

Flag combos

Combo	Meaning	Example
`cat -n file \| head`	Numbered preview	`cat -n app.log \| head`
`cat a b > c`	Concatenate into new file	`cat part1 part2 > all`

`less`

Definition: Page through a file interactively (scroll, search, follow).

Option	Argument	Meaning	Example
(none)	`FILE`	Interactive pager (scroll/search)	`less /var/log/syslog`
`-N`	`FILE`	Show line numbers	`less -N file`
`-S`	`FILE`	Chop long lines (no wrap)	`less -S wide.log`
`-i`	`FILE`	Search ignore case	`less -i file` then `/error`
`-F`	`FILE`	Quit if one screen	`less -F short`
`-R`	`FILE`	Raw ANSI colors	`less -R colored.log`
`+F`	`FILE`	Start in follow mode (like tail -f)	`less +F app.log`
`+/PAT`	`FILE`	Open at first match	`less +/ERROR app.log`

Inside less (keys):

q quit · /pat search · n next · g top · G end · F follow · Ctrl-C stop follow

Flag combos

Combo	Meaning	Example
`less -NS file`	Numbers + chop	`less -NS access.log`

`head`

Definition: Show the first lines (or bytes) of a file.

Option	Argument	Meaning	Example
(none)	`FILE`	First 10 lines (default)	`head file`
`-n`	`N FILE`	First N lines	`head -n 20 file`
`-n`	`-N FILE`	All but last N lines (GNU)	`head -n -5 file`
`-c`	`N FILE`	First N bytes	`head -c 100 file`
`-q`	`FILE...`	Never print filename headers	`head -q *.log`
`-v`	`FILE`	Always print headers	`head -v a b`

Flag combos

Combo	Meaning	Example
`head -n 5`	Quick sample	`head -n 5 /etc/passwd`

`tail`

Definition: Show the last lines of a file; with -f, follow live appends.

Option	Argument	Meaning	Example
(none)	`FILE`	Last 10 lines	`tail file`
`-n`	`N FILE`	Last N lines	`tail -n 50 app.log`
`-n`	`+N FILE`	From line N to end	`tail -n +100 file`
`-c`	`N FILE`	Last N bytes	`tail -c 200 file`
`-f`	`FILE`	Follow append (live log)	`tail -f app.log`
`-F`	`FILE`	Follow by name; retry if rotated	`tail -F /var/log/app.log`
`--pid`	`PID`	With `-f`: stop when PID dies	`tail -f log --pid=1234`
`-q`	`FILE...`	No headers	`tail -q *.log`

Flag combos

Combo	Meaning	Example
`tail -n 100 -f log`	Last 100 then follow	`tail -n100 -f app.log`
`tail -F log`	Survive logrotate	Production agents

`wc`

Definition: Count lines, words, and/or bytes in input.

Option	Argument	Meaning	Example
(none)	`FILE`	Lines, words, bytes	`wc file`
`-l`	`FILE`	Line count only	`wc -l app.log`
`-w`	`FILE`	Word count	`wc -w file`
`-c`	`FILE`	Byte count	`wc -c file`
`-m`	`FILE`	Character count	`wc -m file`
`-L`	`FILE`	Length of longest line (GNU)	`wc -L file`

Flag combos

Combo	Meaning	Example
`grep ERR log \| wc -l`	Count matches	`grep -c` also works

`file`

Definition: Guess a file’s type from content (magic), not just the name.

Option	Argument	Meaning	Example
(none)	`PATH`	Guess type from content/magic	`file /bin/ls`
`-b`	`PATH`	Brief; no filename prefix	`file -b x`
`-i`	`PATH`	MIME type	`file -i doc`
`-L`	`PATH`	Follow symlinks	`file -L link`
`-s`	`PATH`	Read special files (block/char)	`file -s /dev/sda`
`-z`	`PATH`	Look inside compressed	`file -z a.gz`

Flag combos

Combo	Meaning	Example
`file *`	Type all in dir	Quick triage

`stat`

Definition: Show detailed inode metadata: size, mode, owner, timestamps.

Option	Argument	Meaning	Example
(none)	`PATH`	Size, mode, uid/gid, timestamps, inode	`stat file`
`-c`	`FORMAT PATH`	Custom format (GNU)	`stat -c '%n %s %a' f`
`-f`	`PATH`	Filesystem status (like df)	`stat -f /`
`-L`	`PATH`	Follow symlink	`stat -L link`
`-t`	`PATH`	Terse one line	`stat -t file`

Useful `-c` formats:

%n name · %s size · %a octal mode · %A human mode · %U/%G owner · %y mtime

Flag combos

Combo	Meaning	Example
`stat -c '%a %n' f`	Octal mode + name	Permission checks
`stat -c '%y %n' f`	Mtime

Common recipes

Goal	Command
Sample start of log	`head -n 20 app.log`
Sample end of log	`tail -n 50 app.log`
Live follow	`tail -f app.log`
Page a large file	`less app.log`
Line count	`wc -l app.log`
Is it binary?	`file ./artifact`
Mode + owner + size	`stat file` or `ls -l file`

Pitfalls

cat huge logs floods the terminal — prefer less / tail.
tail -f follows the inode; after rotate use tail -F.
file is a guess — not security proof.
Binary files: less may warn; don’t cat binaries into an SSH session.

For more details, try man <command> in your terminal.

Must-know cold

Commands

cat

Flag combos

less

Inside less (keys):

Flag combos

head

Flag combos

tail

Flag combos

wc

Flag combos

file

Flag combos

stat

Useful -c formats:

Flag combos

Common recipes

Pitfalls

Must-know cold

Commands

cat

Flag combos

less

Inside less (keys):

Flag combos

head

Flag combos

tail

Flag combos

wc

Flag combos

file

Flag combos

stat

Useful -c formats:

Flag combos

Common recipes

Pitfalls

`cat`

`less`

`head`

`tail`

`wc`

`file`

`stat`

Useful `-c` formats:

`cat`

`less`

`head`

`tail`

`wc`

`file`

`stat`

Useful `-c` formats: