Command Line Foo
A collection of handy tips and tricks for the Unix command line.
Good reference: http://www.commandlinefu.com/
See also:
- http://cfenollosa.com/misc/tricks.txt
- https://developer.atlassian.com/blog/2015/02/ten-tips-for-wonderful-bash-productivity/
- Gentoo's Bash scripting guide
# A useful prompt
PS1='\[\e]0;\w\a\]\n\[\e[32m\]\u@\h \[\e[33m\]\w\[\e[0m\]\nλ '
# Avoid tty session timeouts
export TMOUT=0
# SSH escape sequences
# From: https://lonesysadmin.net/2011/11/08/ssh-escape-sequences-aka-kill-dead-ssh-sessions/
~. - terminate connection (and any multiplexed sessions)
~B - send a BREAK to the remote system
~C - open a command line
~R - Request rekey (SSH protocol 2 only)
~^Z - suspend ssh
~# - list forwarded connections
~& - background ssh (when waiting for connections to terminate)
~? - this message
~~ - send the escape character by typing it twice
# Retrieve arguments from previous command
!^ first argument
!$ last argument
!* all arguments
!:2 second argument
!:2-3 second to third arguments
!:2-$ second to last arguments
!:2* second to last arguments
!:2- second to next to last arguments
!:0 the command
!! repeat the previous line
!n repeat command n from the history
!-n repeat command from -n entries in the history
# Find out Linux release version
uname -a
lsb_release -a
cat /etc/redhat-release
cat /etc/lsb-release
# Rerun previous command with sudo in front
sudo !!
# Disable <CTRL-d> which is used to logout of a login shell
# (local or remote login session over ssh).
set -o ignoreeof
# Compare directories
diff --suppress-common-lines -y \
<(cd liquidity-orchestrator-7.1.10.1; find . | sort) \
<(cd ../liquidity-orchestrator-8.0.0-SNAPSHOT; find . | sort)
# Compare tarballs
diff --suppress-common-lines -y \
<(tar tzf liquidity-orchestrator-8.0.0.tgz | sed 's/[^/]*\/\(.*\)/\1/' | sort) \
<(tar tzf liquidity-orchestrator-7.1.11.0.1.tgz | sed 's/[^/]*\/\(.*\)/\1/' | sort)
# Practical networking with netcat
# http://aplawrence.com/Girish/nc.html
# Check connectivity
nc -vw 1 <ip> <port>
or
nc -z <ip> <port>
# Bash only
(echo > /dev/tcp/x.x.x.x/443) >/dev/null 2>&1 && echo "It's up" || echo "It's down"
# Listen on a port
nc -l <port>
# Listen on a port - keep connection listening
nc -lk <port>
# Find out which process is using a given port
lsof -i :<port number>
# Find large files
find . -type f -size +50000k -exec ls -lh {} \;
# Disk quotas
quota -s
du -h --apparent-size
# bash lookup maps
declare -A property_names
property_names["liquidity-connector-reuters-mapi"]="reutersmapi"
property_names["liquidity-connector-gain-gtx"]="gaingtx"
property_names["liquidity-connector-fxcmpro"]="currenex"
property_names["liquidity-connector-cme-fix"]="cme"
property_names["mda-fxall-iex"]="fxall"
# Checking for CPU power saving settings\
# (AKA green or tree hugging settings)
watch -n 1 'for f in /proc/acpi/processor/*; do grep active $f/power;done'
watch -n 1 'for f in /proc/acpi/processor/*; do grep active $f/power;done | grep -v C1'
for i in /proc/acpi/processor/*; do echo $i; more $i/* | \
egrep "active state|power management|throttling control"; done
# Turn off VI auto-indent on pasting
:set paste
(optional: after pasting) :set nopaste
# Run a script on a remote box via SSH (via http://linux.icydog.net/ssh/piping.php)
ssh user@server 'bash -s' < script.sh
# Find out cannonical path for a file
readlink -f <file>
# Handy FIX commands
cat fix.log | sed 's/\x01/|/g'
# DNS lookup commands
# standard lookup cmd
nslookup <host>
# dig is much more flexible. For a super short answer, ideal for scripting:
dig +short +search <host>
# Reverse lookup
dig +short -x <ip_addr>
# Remote Desktop access spanning multiple monitors
mstsc /span
# AWK histograms
# http://braindump.mrzesty.net/index.php?node=63
awk '{data[c]=$1; c++; a+=$1} END {\
asort(data);\
print "min=" data[1] ", max=" data[NR] ", median=" a/NR \
", 50%=" data[int(NR/2-0.5)] ", 95%=" data[int(NR*0.95-0.5)] \
", 99%=" data[int(NR*0.99-0.5)]}'
# Rsync args
rsync -avz $EXCLUDE_DIRECTIVES $REF_LOCATION $REMOTE_URI
# Find which processes are assigned to which CPU
ps -aeww -o pid,psr,args | sort -k 2n
# Find which process threads are assigned to which CPU
ps -aLeww -o pid,lwp,psr,args | sort -k 3n
or
ps -eLF
# List all process's threads
ps -LFp <PID>
# List all process's thread's affinity settings
taskset -acp <PID>
# List LWP affinity settings
taskset -cp <LWP_ID>
# Get JVM thread dump
jstack <PID>
# List JVM thread LWP_IDs (converting jstack's hex output to decimal along the way...)
jstack <PID> | grep nid= | sed 's/\("[^"]*"\).*nid=\([^ ]*\) .*/printf "%d %s" \2 \1/e'
# Check core isolation settings on host
cat /proc/cmdline
# List all groups available on the host
getent group
# CPU performance counters
# See http://blog.monitorscout.com/2014/06/26/accurate-cpu-usage-measurement-on-linux/
cat /proc/stat
# Handling both stdin and arguments from functions
# From https://unix.stackexchange.com/questions/301426/bash-function-that-accepts-input-from-parameter-or-pipe
my_function() {
if (( ${#} == 0 )) ; then
while read -r __my_function ; do
my_function "${__my_function}"
done
else
target_utility "${@}"
fi
}
# or
b64decode() {
if [ "$#" -ne 0 ]
then
printf '%s\n' "$1"
else
cat
fi | base64 --decode
echo
}
# or
b64decode() {
(
if [ "$#" -ne 0 ]
then
exec <<< "$1"
fi
base64 --decode
echo
)
}
# Argument parsing
# From http://stackoverflow.com/questions/192249/how-do-i-parse-command-line-arguments-in-bash
while [ "$#" -ge 1 ]; do
key="$1"
case $key in
-e|--extension)
EXTENSION="$2"
shift # past argument
;;
-s|--searchpath)
SEARCHPATH="$2"
shift # past argument
;;
-l|--lib)
LIBPATH="$2"
shift # past argument
;;
--default)
DEFAULT=YES
;;
*)
# unknown option
;;
esac
shift
done
