More Commands

file utilities

wc /etc/passwd  # count lines, words, characters
wc -l /etc/passwd  # lines only
wc -w /etc/passwd  # words only
wc -c /etc/passwd  # chars only
wc -L /etc/passwd  # length of longest line

file /etc/fstab  # ASCII text
file /usr/bin/gunzip  # shell script
file /bin/ls  # ELF 64-bit LSB executable (binary)
file /usr/share/man/man1/less.1.gz  # gzip compressed data (man page for less)

od -ta /etc/fstab  # shows non-printing chars as char names
od -tc /etc/fstab  # shows non-printing chars as C escapes
od -tx1 /etc/fstab  # shows chars as hex numbers
strings -n16 /bin/sh  # 16+ consecutive printing chars (in binary file)

cat > foo0  # create a file (original)
line 1
lime 2  # misspelled
Ctrl+d
cat > foo1  # create another file (new and improved)
line 1
line 2  # corrected
Ctrl+d
diff foo0 foo1  # show differences between two files (line editor format)
diff foo0 foo1 | tee foo01.diff  # create and display update file
cmp -l foo0 foo1  # binary compare, -l shows which bytes differ

rm foo0 foo1 foo01  # clean up

system info

hostname  # shows hostname
uname  # shows UNIX name
uname -a  # (all) shows more information
uptime  # shows how long the system has been running and CPU load averages

quota  # shows disk quota (if any) on your account
df -h  # shows disk space free in each mounted filesystem, human readable
du -hs /etc  # shows disk space used in specified directory
du -ks /etc 2> /dev/null  # kilobytes, discards error messages
vmstat -d  # disk status
vmstat -SM  # memory status (MB)
free  # memory, Linux only

ip addr  # interface addresses
ip route  # routing table
ip neighbor  # same LAN

user info

whoami  # shows your login name
id  # shows UserID, GroupID, and groups
users  # (similar to who, finger) shows users logged in
w  # shows uptime, users logged in, and what they're doing
finger $USER  # this shows information about you
finger stuart  # this shows another user
last | less  # shows recent logins
q  # quit less
ac  # accounting, total connect time in hours
ac $USER  # your connect time
ac -p  # every person's connect time
ac $USER -d  # your connect time by day

dates

date  # shows time and date
date +%s  # seconds since epoch (1970 Jan 01), many other format options
cal  # shows calendar for current month
cal 5 2026  # shows calendar for May 2026
cal 2026 | less  # shows calendar for all of 2026 CE
q  # quit less

fun

fortune # shows a random fortune cookie