shell-mastery — Server Survival

Quick Survival Commands (any Linux server)

Where am I, who am I

whoami; hostname; uname -a; cat /etc/os-release
pwd; echo $SHELL; echo $0

What shell is available

cat /etc/shells
chsh -l               # same thing on some distros
echo $SHELL            # current default
echo $0                # current running shell

If only sh is available (POSIX-only survival)

# No arrays, no [[ ]], no process substitution
# Use: [ ], $(cmd), test, case, while read
while IFS= read -r line; do
  case "$line" in
    *error*) echo "FOUND: $line" ;;
  esac
done < logfile.txt

Check what tools exist

for cmd in vim vi nano awk sed perl python3 python curl wget jq yq; do
  command -v "$cmd" >/dev/null 2>&1 && printf "%-10s %s\n" "$cmd" "$(command -v $cmd)" || printf "%-10s MISSING\n" "$cmd"
done

History tricks (works in bash and zsh)

!!           # repeat last command
!$           # last argument of previous command
!^           # first argument of previous command
!:2          # second argument of previous command
!cmd         # run most recent command starting with 'cmd'
^old^new     # replace old with new in last command
ctrl-r       # reverse search history