Bash Tips and Tricks
Use “Exit Traps” to make scripts more robust and reliable
You can place any code that you want to be certain to run in this “finish” function.
#!/bin/bash
function finish {
# Your cleanup code here
}
trap finish EXIT
More info: here
Use Bash Strict Mode (Unless You Love Debugging!)
Add this in your scripts to cause them exit immediately in case of errors, bugs, and exceptions.
#!/bin/bash
set -euxo pipefail
# which is the short version of:
set -e
set -u
set -o pipefail
set -x
Read more from here to understand what each does.
Run a specific command on a specific CPU(s)
# This will run the command on cpu 3:
$ taskset -c 3 command
# This will run the command on cores 64-127:
$ taskset -c 64-127 command
Download multiple links with axel
while read url; do axel -n 10 $url; done < myLinks
Redirect the command output
- Redirect stdout to one file and stderr to another file:
command > out 2>error
- Redirect stdout to a file (>out), and then redirect stderr to stdout (2>&1):
command >out 2>&1
- Redirect both to a file (this isn’t supported by all shells, bash and zsh support it, for example, but sh and ksh do not):
command &> out
More detailed methods: (got from here)
|| visible in terminal || visible in file || existing
Syntax || StdOut | StdErr || StdOut | StdErr || file
==========++==========+==========++==========+==========++===========
> || no | yes || yes | no || overwrite
>> || no | yes || yes | no || append
|| | || | ||
2> || yes | no || no | yes || overwrite
2>> || yes | no || no | yes || append
|| | || | ||
&> || no | no || yes | yes || overwrite
&>> || no | no || yes | yes || append
|| | || | ||
| tee || yes | yes || yes | no || overwrite
| tee -a || yes | yes || yes | no || append
|| | || | ||
n.e. (*) || yes | yes || no | yes || overwrite
n.e. (*) || yes | yes || no | yes || append
|| | || | ||
|& tee || yes | yes || yes | yes || overwrite
|& tee -a || yes | yes || yes | yes || append
(*) Bash has no shorthand syntax that allows piping only StdErr to a second command, which would be needed here in combination with tee again to complete the table. If you really need something like that, please look at “How to pipe stderr, and not stdout?” on Stack Overflow for some ways how this can be done e.g. by swapping streams or using process substitution.
Disable the annoying bell in bash
- To disable the beep in bash you need to uncomment (or add if not already there) the line
set bell-style nonein your/etc/inputrcfile.
Note: Since it is a protected file you need to be a privileged user to edit it (i.e. launch your text editor with something like sudo <editor> /etc/inputrc).
To disable the beep also in vim you need to add
set visualbellin your~/.vimrcfile.To disable the beep also in less (i.e. also in man pages and when using
git diff) you need to addexport LESS="$LESS -R -Q"in your~/.profilefile.
Make your prompt look nicer
- Put this line inside of .bashrc
export PS1="\[\033]0;$TITLEPREFIX:$PWD\007\]\n\[\033[32m\]\u@\h \[\033[35m\]$MSYSTEM \[\033[33m\]\w\[\033[36m\]\[\033[0m\]\n$ "
Display all IP addresses connected to your host
netstat -lantp | grep ESTABLISHED |awk '{print $5}' | awk -F: '{print $1}' | sort -u
List the commands you use more often
history | awk '{a[$2]++}END{for(i in a){print a[i] " " i}}' | sort -rn | head
Helpful aliases
- Put these aliases in .bashrc
alias c='clear'
alias cd..='cd ..'
alias ..='cd ..'
alias ...='cd ../../../'
alias ....='cd ../../../../'
alias .....='cd ../../../../../'
alias .2='cd ../../'
alias .3='cd ../../../'
alias .4='cd ../../../../'
alias .5='cd ../../../../..'
alias mkdir='mkdir -pv'
alias diff='colordiff'
alias h='history'
alias histg="history | grep"
alias now='date +"%T"'
alias nowtime=now
alias nowdate='date +"%d-%m-%Y"'
alias vi='vim'
alias svi='sudo vi'
alias vis='vim "+set si"'
alias edit='vim'
alias ports='netstat -tulanp'
alias su='sudo -i'
alias reboot='sudo /sbin/reboot'
alias poweroff='sudo /sbin/poweroff'
alias halt='sudo /sbin/halt'
alias shutdown='sudo /sbin/shutdown'
alias meminfo='free -m -l -t'
alias psmem='ps auxf | sort -nr -k 4'
alias psmem10='ps auxf | sort -nr -k 4 | head -10'
alias pscpu='ps auxf | sort -nr -k 3'
alias pscpu10='ps auxf | sort -nr -k 3 | head -10'
alias gpumeminfo='grep -i --color memory /var/log/Xorg.0.log'
alias wget='wget -c'
alias df="df -Tha --total"
alias psg="ps aux | grep -v grep | grep -i -e VSZ -e"
alias top="htop"
alias myip="curl http://ipecho.net/plain; echo"
alias DU="du --max-depth=1 -B M |sort -rn"
alias filecount="find . -type f 2> /dev/null | wc -l"
Some useful user config
Put these into the file ~/.inputrc:
# Place this file into your home directory
# none, visible or audible
set bell-style visible
# Ignore case for the command-line-completion functionality
# on: default on a Windows style console
# off: default on a *nix style console
set completion-ignore-case on
set colored-stats On
set completion-ignore-case On
set completion-prefix-display-length 3
set mark-symlinked-directories On
set show-all-if-ambiguous On
set show-all-if-unmodified On
set visible-stats On
Query the linked libraries of an executable
To see which libraries have been linked to a specific executable, e.g. mpirun
ldd `which mpirun`
Query the executable header, e.g. check RUNPATH entry
readelf -d /home/sojoodi/projects/def-queenspp/sojoodi/OpenMPI-Debug/build/bin/mpirun | grep RUNPATH
LD_PRELOAD Trick
In summary, you can preload the specified shared libraries at runtime to resolve some conflicts happened at link-time, or to overright any previously statically bound libraries, like stubs. For instance, if you want to preload NVIDIA ML library to make sure your program points at the current location at runtime, you can do something like the following:
export LD_PRELOAD=/usr/lib64/nvidia/libnvidia-ml.so
/path/to/executable
To find more information about LD_PRELOAD trick, read here.